Mechanically compliant and cost-effective 1.4Li_2O-0.75ZrCl_4-0.25AlCl_3 solid electrolyte for all-solid-state batteries with improved cycling stability

Domain: physics
Published: 2026-01-08
Editorial outcome: major_revision

Abstract
Although Li-ion conductivity has been the primary focus during decades of solid-electrolyte research, the mechanical compliance is equally important. For most state-of-the-art solid electrolytes, the mechanical compliance is characterized by the hardness above 1 GPa and Young’s modulus above 15 GPa. Here, we report a particularly compliant solid electrolyte, 1.4Li2O-0.75ZrCl4-0.25AlCl3, whose hardness and Young’s modulus reach 0.22 and 1.41 GPa, respectively. Meanwhile, it shows an ionic conductivity of 2.55 mS cm−1 at 25 °C and an estimated cost of $43.70 L−1, considerably lower than that of the Li2ZrCl6 solid electrolyte known for cost-effectiveness ($140.01 L−1). The improved mechanical compliance and fast Li-ion transport in 1.4Li2O-0.75ZrCl4-0.25AlCl3 enable decent cell performance. With high positive electrode active material loading above 20 mg cm−2, these two types of cells achieve areal capacities of 3.62 mAh cm−2 (85.78% capacity retention) and 3.92 mAh cm−2 (90.11% capacity retention), respectively, after 100 cycles under 0.1 C at 25 °C. The simultaneous achievement of highly competitive mechanical compliance, Li-ion conductivity, and cost-effectiveness in 1.4Li2O-0.75ZrCl4-0.25AlCl3 have the potential to pave the way for the realization of commercial, practical all-solid-state Li batteries.

Introduction
Efficient Li-ion transport, high mechanical compliance, and strong cost-competitiveness are three indispensable characteristics for the solid electrolyte in all-solid-state Li batteries (ASSLBs)1–3; while other properties like electrochemical stability and Li dendrite suppressing capability are replaceable by alternative approaches such as electrode coating4–6 and Ag-C interlayers7, respectively, these characteristics cannot. Among the three of them, the importance of mechanical compliance to the overall cell performance is in fact no lower than that of the much more extensively studied Li-ion conductivity, because only the highly compliant solid electrolytes can deform efficiently under pressure to maintain the intimate contact with the repeatedly expanding and contracting electrode active materials8–10.

The mechanical compliance of solid electrolytes would become particularly essential under the cycling conditions that are closer to practical situations. Presently, to demonstrate the advantages associated with the increasingly high ionic conductivities of solid electrolytes (many exceeding 1 mS cm−1 at 25 °C11–18, and some even above 10 mS cm−1 at 25 °C4,19–22), the cells with typical positive electrodes (e.g., LiCoO2 and LiNi0.8Co0.1Mn0.1O2) are often cycled at 1 C−5 C in literature3,12,23–26, while higher rates of 20 C−50 C were also adopted occasionally27–30. Nevertheless, in practical situations, high-rate cycling is not the only demand. Taking electric vehicles as an example, although the charge still need to be as fast as possible, the discharge does not. Assuming a vehicle with a 600 km range driven no faster than 120 km h−1, the average discharge rate would not exceed 0.2 C, so most of the time the actual discharge rate should vary between 0.1 C and 0.3 C, much lower than the frequently used 1 C−5 C rates for testing3,12,23–30. Such low cycling rate is usually associated with larger capacity; for example, the capacity of LiNi0.88Co0.07Mn0.05O2 at 0.2 C has been reported to be 178.6% of that at 4 C12. Therefore, more Li ions would be actually inserted to or extracted from the crystal at low cycling rates, making the positive electrode active material (PEAM) particles undergo larger volume change. To sustain the intimate contact with the PEAM particles under these circumstances, the solid electrolytes have to be much more compliant. In particular, such demand would be more compelling when the areal capacity increases from the commonly adopted 1 mAh cm−2 for laboratory testing to the level for enabling high energy densities (around or above 4 mAh cm−2).

In order to rationally improve the mechanical compliance, the metrics for this characteristic need to be properly identified first. In the studies on mechanical properties, the Young’s modulus has been frequently emphasized, but it is not the only important metric for mechanical compliance31,32. In fact, what Young’s modulus describes is the elastic deformation, which is often limited to the initial, low-stress stage of the solid-electrolyte deformation during cycling8,10,33. When the stress is sufficiently large, plastic deformation would occur. The resulting plastic flow would enable much more efficient morphology change than elastic deformation, and thus usually plays a main role in sustaining the intimate solid-solid contact during cycling8,10. Therefore, how difficult it is to induce plastic deformation in a solid electrolyte (reflected by its hardness) is also a critical metric. In literature, the hardness and Young’s modulus have been identified as the two major factors underpinning the intactness of the electrode-electrolyte contact of all-solid-state cells during cycling, and preferably both of them should be as low as possible10. However, the present inorganic solid electrolytes known to be highly compliant, i.e., the sulfide and halide solid electrolytes, generally show the hardnesses above 1 GPa and Young’s moduli above 15 GPa3,8,34–37. Besides, most (if not all) of these solid electrolytes may be too costly to enable the successful commercialization of ASSLBs38.

Here, we report a 1.4Li2O-0.75ZrCl4-0.25AlCl3 solid electrolyte, which simultaneously achieves the hardness and Young’s modulus of 0.22 and 1.41 GPa, respectively, at a decent cost. Combined with a high ionic conductivity of 2.55 mS cm−1 at 25 °C in the meantime, this mechanical compliance allows the all-solid-state cell with LiNi0.92Co0.06Mn0.02O2 to deliver an areal capacity of 3.92 mAh cm−2 and a capacity retention of 90.11% after 100 cycles at 25 °C.

Results
Materials design principles and Li-ion transport behaviors
Our materials design strategy for realizing high mechanical compliance is based on two principles. First of all, compared with the materials with only one type of anion, those with two types of anions have often been found to display the kind of atomic configuration that enables higher mechanical compliance25,39,40. In such materials, the coexisting anions frequently make the cation-anion polyhedra more distorted and disordered, so that the backbone of the atomic framework becomes more easily rotated or bended, leading to enhanced mechanical compliance25,39,40; this phenomenon has been observed in multiple solid electrolytes, including the O-modified Na3PS440, Li2ZrCl63,25, and LiAlCl439. Based on this principle, oxysulfides and oxychlorides are both promising candidates. However, since oxysulfides are rather difficult to meet the cost-effectiveness requirement for commercialization due to the expensive raw material Li2S38, the present study will focus on oxychlorides. Secondly, among the oxychloride solid electrolytes mentioned above, the amorphous status is often associated with much higher mechanical compliance than the crystalline form3,25,39,41,42. Taking this phenomenon into account too, our focus is placed on amorphous oxychlorides. While this type of material is promising in achieving decent mechanical compliance, the other two “indispensable characteristics” mentioned in the Introduction, i.e., efficient Li-ion transport and strong cost-competitiveness, must also be considered. In order to realize Li-ion conductivity above 1 mS cm−1 at 25 °C, the oxychlorides usually need to contain non-Li cations3,16,21,24,25,42–45. Recently, Ta5+ was found to be a particularly effective non-Li cation for realizing fast Li-ion transport; Ta-based oxychlorides such as 1.6Li2O-TaCl5 and LiTaOCl4 display ionic conductivities up to 12.4 mS cm−1 at 25 °C21,24. However, the raw material TaCl5 is known to be too costly to enable the commercialization of ASSLBs38. Fortunately, the ionic radius of Ta5+ happen to lie between those of Zr4+ and Al3+46, whose raw materials ZrCl4 and AlCl3 are both rather cost-effective42,47. If Zr4+ and Al3+ coexist in the amorphous oxychloride at a proper molar ratio, the non-Li cations may reach an effective ionic radius close to that of Ta5+, but without inducing unacceptably high costs. Therefore, with the mechanical compliance, Li-ion conductivity, and cost-effectiveness all taken into account, the amorphous xLi2O-(1-y)ZrCl4-yAlCl3 oxychlorides seem a highly promising materials system.

Based on this hypothesis, we tried to prepare a series of amorphous xLi2O-(1-y)ZrCl4-yAlCl3 oxychlorides by planetary milling the stoichiometric mixtures of Li2O, ZrCl4, and AlCl3 for 30 h (milling parameters are specified in Methods). As shown in Fig. 1a and Supplementary Fig. 1, the materials with x=1.0−1.8 and y=0.2−0.5 display high ionic conductivities that are close to or above 1 mS cm−1 at 25 °C, and their electronic conductivities are orders of magnitude lower (Supplementary Fig. 2), confirming that these oxychlorides can serve as solid electrolytes in ASSLBs. For each series of compositions with a given y, the ionic conductivity peaks at x=1.4 (Fig. 1a). Among these x=1.4 compositions with different y values, the most efficient Li-ion transport is realized at y=0.25 (Fig. 1b, c), i.e., the 1.4Li2O-0.75ZrCl4-0.25AlCl3 oxychloride (abbreviated as LZACO below); it shows an ionic conductivity of 2.55 mS cm−1 at 25 °C and an activation energy of 0.276 eV (the corresponding Arrhenius plots are displayed in Supplementary Fig. 3). Consistently with the hypothesis raised above, the Zr/Al molar ratio in this optimal composition happens to make the equivalent ionic radius of non-Li cations close to that of Ta5+ (0.67 vs. 0.64 Å for the coordinate number 6, and this holds for other coordinate numbers too46), whose presence in oxychlorides is often accompanied by high Li-ion conductivities21,24.

In addition to the ionic conductivity, the structures also meet our expectations. The X-ray diffraction (XRD) patterns suggest that all of the materials discussed above are indeed almost completely amorphized (a few representative examples shown in Fig. 1d, e). The pair distribution function (PDF) analysis based on neutron total scattering is also indicative of the same scenario. Supplementary Fig. 4 shows the PDF of LZACO obtained by neutron total scattering, as well as the simulated PDFs of LZACO with the P3̅m1 structure and that with the C2/m structure. In comparison with the two crystalline forms of LZACO, the actual LZACO displays much weaker and broader peaks in the PDF, confirming its high degree of amorphization. Beyond the qualitative evaluations above, we also conducted high-resolution transmission electron microscopy (TEM) observation to probe the volume fraction of the amorphous species in LZACO. As shown in Supplementary Fig. 5a, the volume of the crystalline phase in LZACO is so low that almost no lattice fringe is visible in the as-collected, unprocessed high-resolution TEM (HRTEM) image. Only after the fast Fourier transform (FFT), the two weak spots indicating the existence of crystallites are disclosed (Supplementary Fig. 5b). The size and morphology of the crystalline regions can be probed by conducting inverse FFT using these two weak spots. As shown in Supplementary Fig. 5d, such processing discloses one relatively large crystalline region at the left side of the image and several scattered, small ones. Unlike the former, the latter should be the artifacts resulting from the inverse FFT processing, rather than true crystallites; when FFT was conducted locally at different regions in Supplementary Fig. 5c, the aforementioned relatively large crystalline region is in fact the only one that can give rise to spots in the FFT pattern (Supplementary Fig. 5e), and the same happens to none of the other regions (examples shown in Supplementary Fig. 5f). In this way, Supplementary Fig. 5d in fact suggests that the size of the rare crystallites in LZACO is about 15 nm. Such a crystallite size explains why the PDF of the highly amorphous LZACO material (Supplementary Fig. 4) still shows weak peaks characterizing ordered crystalline structures up to r=30 Å (3 nm). More importantly, Supplementary Fig. 5d also indicates that the crystalline phase only occupies 10 vol% in LZACO, with the remaining volume being amorphous. It must be emphasized that the compositions of such minor crystalline species are not necessarily identical with those of the amorphous matrix. Instead, it might be the Li-M-Cl (M=Zr and/or Al) precipitates, which are much more difficult to amorphize than the oxychlorides25,42. The precise composition determination for the minor crystalline phases here would require the elemental mapping at magnifications no lower than those in the HRTEM image presented above (Supplementary Fig. 5a), but the intense electron beam needed for such characterization would rapidly damage the electron-beam-sensitive oxychloride solid electrolytes. Consequently, the composition of the crystalline phase cannot be conclusively determined. Fortunately, their volume fraction (about 10% as mentioned above) is too low to considerably influence the overall ion transport. Although the low crystallinity of xLi2O-(1-y)ZrCl4-yAlCl3 prevents the precise crystal structure determination, the XRD patterns may still disclose certain information regarding the atomic configuration. Generally speaking, the characteristic reflections of up to two types of crystal structures can be identified; both have been frequently observed in the Li3MCl6-type chloride solid electrolytes48. One of them is the structure showing the hexagonal close-packed (hcp) anion arrangement; the materials displaying this kind of structure include the Li2ZrCl6 with the P3̅m1 space group47,49 and the Li3YCl6 with the Pnma space group48. The other is the structure showing the cubic close-packed (ccp) anion arrangement; the materials displaying this type of structure include the LiCl with the Fm3̅m space group48 and the Li3ScCl6 with the C2/m space group50. Due to the low crystallinity of LZACO, it is difficult to conclusively determine which specific structures mentioned above is displayed by each phase. Consequently, the two crystalline phases present in LZACO would be generally referred to as the hcp and ccp phases, respectively, in the discussion below. For the xLi2O-(1-y)ZrCl4-yAlCl3 materials studied here, the hcp phase would transform into the ccp phase as either x or y increases, with the intermediate compositions displaying these two phases simultaneously (Fig. 1d, e). Similar to a recently reported high-performance solid electrolyte Li1.75ZrCl4.75O0.53, the most Li-ion conductive LZACO material identified above is also an “intermediate composition” showing the coexisting hcp and ccp phases. The simultaneous presence of these energetically comparable states is believed to make the material more easily amorphized3, while the resulting large contents of amorphous species have been demonstrated to be the major enabling factor for the fast Li-ion transport in multiple Zr-based oxychlorides3,16,25,26,44,45. Likewise, the high ionic conductivity of LZACO also originates from the amorphous species. Once the crystallinity is improved by annealing at 300 °C for 5 h, its ionic conductivity would drop by more than one order of magnitude (Supplementary Fig. 6). Although both LZACO and the previously reported Li-Zr-Cl-O oxychlorides rely on the amorphous phase to realize fast Li-ion transport, the specific atomic configurations in their amorphous phases are not the same, which lead to different ion transport efficiencies. In the Li-Zr-Cl-O oxychlorides, the averaged Zr-O and Zr-Cl bond lengths in the distorted Zr-O/Cl polyhedra are believed to be the key to the high ion transport efficiency, as they flatten the energy landscape for Li-ion migration to lower the overall migration barriers25. Such a disordered atomic arrangement also occurs in LZACO, but to a more pronounced degree. To characterize this behavior, we conducted X-ray absorption spectroscopy (XAS). As shown in Supplementary Fig. 7a, the Zr K-edge X-ray absorption near-edge structure (XANES) spectrum of LZACO does not show distinct peaks like those of ZrO2 and ZrCl4, but appears as a broad hump, entailing that the Zr-Cl and Zr-O bond lengths in LZACO vary in a range, instead of displaying definitive values. On this basis, more interesting behaviors were observed in the Fourier transformed extended X-ray absorption fine structure (FT-EXAFS) spectra. Unlike other Li-Zr-Cl-O solid electrolytes25, the Zr-O and Zr-Cl signals in LZACO are not distinguishable from each other, but nearly merge into one broad peak (Supplementary Fig. 7b). This observation suggests that the Zr-O and Zr-Cl bond lengths in LZACO distribute in a broader range than those in the Li-Zr-Cl-O solid electrolytes25. Besides, the FT-EXAFS spectrum of LZACO almost shows no signals above 2.5 Å, entailing the absence of ordering with coherence length exceeding such a distance; in contrast, other Li-Zr-Cl-O solid electrolytes still display minor signals in this range25. Consistent results were observed in the phase-uncorrected wavelet-transformed (WT) EXAFS spectrum, too. While the Zr-O and Zr-Cl bonding still give rise to two distinct signals, respectively, in the Li-Zr-Cl-O solid electrolytes25, they merge together in LZACO (Supplementary Fig. 7c). Besides, the Zr-Zr bonding at about 3 Å in the WT-EXAFS spectra of typical Li-Zr-Cl-O solid electrolytes are absent in that of LZACO too (Supplementary Fig. 7c), confirming the absence of the ordering with such large coherence lengths. These observations consistently suggest that LZACO shows a more disordered atomic configuration than the previously reported Li-Zr-Cl-O solid electrolytes. As mentioned above, such more disordered state should supposedly favor fast Li-ion transport in Zr-based oxychlorides25, which explains the improved ionic conductivity of LZACO with respect to those of other Li-Zr-Cl-O solid electrolytes (2.55 vs. 1−2 mS cm−1 at 25 °C25).

Although the efficient ion transport of LZACO has been confirmed to rely on the amorphous phase that would inevitably crystallize at sufficiently high temperatures, it must also be emphasized that the temperatures typically needed for the fabrication of pouch-cell membranes, i.e., 80−100 °C, are still too low to cause any non-negligible conductivity degradation. To demonstrate this point, we annealed LZACO at 100 °C for 5 h, and probed the associated change of the XRD pattern and ionic conductivity. As shown in Supplementary Fig. 8a, the content of the hcp phase appears to increase slightly with respect to that of the ccp phase after annealing; as the two coexisting phases in LZACO, the hcp and ccp phases must be energetically comparable in this material, so a relatively low energy input, such as that associated with the 100 °C annealing, should be sufficient to alter the ratio between them. Regardless, both of these crystalline phases are still present after annealing, and, more importantly, they continue to occupy a negligibly small fraction in LZACO, as indicated by the diffuse Bragg reflections in the XRD pattern (Supplementary Fig. 8a). Since the majority of LZACO remains the highly Li-ion conductive amorphous species, the material still maintains a high ionic conductivity of 2.23 mS cm−1 at 25 °C, almost identical with that before annealing (2.55 mS cm−1 at 25 °C), as shown in Supplementary Fig. 8b. This observation confirms that the 80−100 °C temperatures needed for fabricating the pouch-cell membranes will not compromise the high Li-ion conductivity of LZACO.

Mechanical compliance
Beyond the efficient Li-ion transport demonstrated above, the solid electrolyte must also display high mechanical compliance, to ensure the formation and maintenance of the intimate solid-solid contact during cycling. As mentioned in the Introduction, the achievement of such high compliance requires not only the Young’s modulus, but also the hardness to be as low as possible. Fig. 2a shows the hardness and Young’s modulus measured for LZACO. For comparison, the data of several other compliant solid electrolytes are also plotted. The Young’s moduli of a few such solid electrolytes were measured too, and the results we obtained align well with those reported in literature (Supplementary Fig. 9), confirming the reliability of our mechanical characterization. As for the hardness, the values for Li1.75ZrCl4.75O0.5 and Li2ZrCl6 are too high to be measured: when nanoindentation was conducted, their cold-pressed pellets did not deform, but collapsed locally into small pieces and loose powders like the cold-pressed pellets of the hard, brittle oxide solid electrolytes, preventing the generation of meaningful load-displacement curves. In contrast, the hardnesses of other solid electrolytes are low enough to enable proper measurements on cold-pressed pellets. Therefore, Li1.75ZrCl4.75O0.5 and Li2ZrCl6 must be no softer than the hardest one among the other solid electrolytes in Fig. 2a, i.e., the Li3InCl6 with 2.07 GPa hardness. With this taken into account, the mechanical compliance of all the aforementioned solid electrolytes can be compared comprehensively in the hardness vs. Young’s modulus plot in Fig. 2a. The data suggest that the hardness and Young’s modulus of LZACO are both considerably lower than those of other solid electrolytes (hardness: 0.22 vs. ≥1.19 GPa; Young’s modulus: 1.41 vs. 7.92−45.75 GPa). To ensure the reliability of these mechanical characterization results, we conducted scanning electron microscopy (SEM) observation on the surface of the cold-pressed LZACO pellet fabricated under 300 MPa (the same as that used for the characterizations above in Fig. 2a). It is found that such a pellet is almost fully densified (Supplementary Fig. 10). In particular, most of the black spots that look like pores are in fact also solid substances too, as shown in the image at higher magnification (Supplementary Fig. 10b); they could be the minor crystalline precipitates that are compositionally different from the amorphous matrix. Using the Adjust-Threshold plugin of ImageJ51, the relative density of the pellet is measured to be 96.13%. Such an almost fully densified pellet ensures the flat, nearly pore-less surface needed for reliable nanoindentation measurements; several representative nanoindentation load-displacement curves acquired from this cold-pressed LZACO pellet are also presented in Supplementary Fig. 11. Here, it must be emphasized that, as a powdery solid electrolyte, the mechanical compliance of LZACO cannot possibly surpass the viscoelasticones, such as the polymer solid electrolytes and the recently reported Li-Al-Cl-O solid electrolytes with unique pliability39,41,42. Instead, the advantage of LZACO in mechanical compliance exists only among the powdery solid electrolytes, which occupy the vast majority of the inorganic solid electrolytes studied so far and appear more compatible with the dry-film technology for pouch-cell fabrication52,53. Such improved mechanical compliance suggests that LZACO must be highly competent in maintaining the intimate solid-solid contact during cycling.

This capability of sustaining the interfacial contact is substantiated both computationally and experimentally. For the computational study, we conducted phase-field modelling to compare LZACO and a compositionally similar solid electrolyte Li1.75ZrCl4.75O0.5 (LZCO), based upon the hardnesses and Young’s moduli displayed in Fig. 2a. Considering that the hardness of LZCO cannot be precisely determined as mentioned above, our computation adopted its lowest possible value, i.e., 2.07 GPa (as indicated in Fig. 2a), to ensure that the estimated mechanical compliance of LZCO is no poorer than reality. Even so, LZCO is still found less effective in maintaining the solid-solid contact than LZACO. As shown in Fig. 2b, when the state of charge (SoC) of the single-crystalline LiNi0.92Co0.06Mn0.02O2 (scNCM92) reaches 0.6, the composite positive electrode layer formed by 75 wt% scNCM92 and 25 wt% LZCO already partially detaches from the LZCO layer it originally contacted with (the region with the order parameter ϕ=1 in Fig. 2b is the detached region). At the SoC of 1.0, their detachment is complete. In contrast, the LZACO layer has not begun to detach from its composite positive electrode layer (formed by 75 wt% scNCM92 and 25 wt% LZACO) at the SoC of 1.0, thereby demonstrating an improved capability of sustaining the solid-solid contact during cycling. To verify the advantage indicated by these computational results, we compared the cycling performance of the actual all-solid-state cells and the interfacial intactness of these cells after cycling. Both experimental observations align rather well with the computational results. The all-solid-state cells assembled for this purpose use scNCM92 as the positive electrode, Li-In alloy as the negative electrode, Li6PS5Cl (LPSCl) as the solid electrolyte contacting the negative electrode, and LZCO or LZACO as the solid electrolyte contacting the positive electrode. To make the difference caused by the mechanical compliance of solid electrolytes more easily observable, we tried to maximize the volume change of the composite positive electrode layer by employing a relatively high PEAM mass loading of around 25 mg cm−2 and a relatively low cycling rate of 0.1 C (20 mA g−1) for both the Li-In | LPSCl-LZCO | scNCM92 and the Li-In | LPSCl-LZACO | scNCM92 cells mentioned above. As shown in Fig. 2c, d, the cycling performances of these two cells do differ greatly from each other. In literature, LZCO has been reported to show satisfactory cycling performance at 25 °C, but only under a very high rate of 1000 mA g−1 (leading to low discharge capacities of 70−100 mAh g−1) and a relatively low PEAM mass loading of 5−6 mg cm−23. In contrast, the Li-In | LPSCl-LZCO | scNCM92 cell studied here (Fig. 2c) was cycled at 25 °C under a much lower rate of 20 mA g−1, which leads to a much higher initial discharge capacity of 176.1 mAh g−1 and thereby a much larger volume change in the PEAM particles. Furthermore, the PEAM mass loading of this cell is more than 4 times that in the aforementioned report (27 vs. 5−6 mg cm−2), which will also result in greater overall volume change. Under this circumstance, the LZCO with limited mechanical compliance can no longer enable decent cycling stability; the discharge capacity drops from 176.1 to 129.3 mAh g−1 only after 10 cycles at 25 °C. In contrast, the LZACO with much lower hardness (0.22 vs. >2.07 GPa) and much lower Young’s modulus (1.41 vs. 7.92 GPa) than LZCO delivered considerably better performance; as shown in Fig. 2d, the discharge capacity of the 1st cycle of the Li-In | LPSCl-LZACO | scNCM92 cell is almost identical with that of the 10th cycle (178.9 and 177.7 mAh g−1, respectively) at 25 °C. After such cycling, we prepared cross-sectional specimens from the composite positive electrodes using focused ion beam (FIB) and examined them using SEM. It should be noted that FIB may cut only about 10 μm deep into the surface of the pellet, which is much smaller than the thicknesses of the composite positive electrode layers with the high PEAM mass loading of around 25 mg cm−2 here (at least tens of micrometers). Therefore, the height of the lamella prepared this way can by no means reflect the thickness of the corresponding composite positive electrode layer. Consistently with the cycling data presented in Fig. 2c, d, the FIB-SEM observation does suggest that LZCO fail to maintain intimate contact with the PEAM particles only after 10 cycles (Fig. 2e); in contrast, LZACO delivered much better performance in this regard (Fig. 2f). Here, it needs to be emphasized that the large voids observed in Fig. 2e must mostly emerge after cycling, instead of pre-existing in as-assembled cells, because otherwise the Li-In | LPSCl-LZCO | scNCM92 cell in Fig. 2c cannot possibly deliver an initial discharge capacity similar to that of the Li-In | LPSCl-LZACO | scNCM92 cell in Fig. 2d (176.1 and 178.9 mAh g−1, respectively). In fact, the volume of voids in the composite positive electrode of the as-assembled Li-In | LPSCl-LZCO | scNCM92 cell is indeed limited; it is comparable to the volume of voids in the Li-In | LPSCl-LZACO | scNCM92 cell after 10 cycles (Supplementary Fig. 12), where no considerable interfacial contact loss is supposed to occur, as indicated by the discharge capacity nearly identical to the initial value (177.7 and 178.9 mAh g−1, respectively). The improved mechanical compliance of LZACO should be the key to maintaining the observed intimate interfacial contact during cycling. With the low hardness and Young’s modulus shown in Fig. 2a, LZACO will deform more easily and significantly at given stresses. Consequently, even if the PEAM particles contacting LZACO undergo significant volume change repeatedly, the LZACO particles can still change their morphologies to keep the intimate solid-solid contact, thereby ensuring the high discharge capacities and decent long-term cycling stability. In practical situations, the ASSLBs tend to employ highest possible PEAM mass loading to maximize the energy density. Besides, as mentioned in the Introduction, the discharge rates would also be relatively low in practice, such as 0.1 C-0.3 C, which will make the discharge capacities with respect to the mass of the PEAM higher than those at high rates. As a result, the overall volume change of both the PEAM particles and the composite positive electrode layer would become more severe, making the highly compliant solid electrolyte like LZACO particularly important for ensuring decent cycling performance. In summary, the computational and experimental data presented in Fig. 2 above consistently suggest that the LZACO solid electrolyte reported here is not plagued by the relatively poor mechanical compliance in typical Zr-based (oxy)chloride solid electrolytes such as the Li2ZrCl6 and LZCO for comparison above. On the contrary, the combined hardness and Young’s modulus of LZACO are comparable with, even surpassing, those of some widely studied sulfide and halide solid electrolytes, as shown in Fig. 2a. Therefore, although many derivatives and chemical modifications of Zr-based (oxy)chloride solid electrolytes have already been reported in literature45,54–56, the LZACO material with the unique advantage in mechanical compliance can still play a distinctive role in ASSLBs.

Cost-effectiveness
In many recent studies, the $50 kg−1 solid-electrolyte cost is referred to as the threshold for the successful commercialization of ASSLBs3,38,57, but this standard is in fact questionable. First and foremost, the solid-electrolyte cost below $50 kg−1 cannot actually ensure that the total production cost of ASSLBs lies below those of commercial Li-ion batteries. Recently, Pasta et al. have conducted an in-depth cost study based on a comprehensive market analysis58. Using the actual cell parameters for the batteries in Volkswagen ID.3, they compared the cost of the energy-dense ASSLBs and the commercial liquid-state Li-ion batteries. Such calculations suggest that the ASSLBs with the aforementioned $50 kg−1 solid-electrolyte cost is still more expensive than the commercial Li-ion batteries ($158 kWh−1 vs. $126 kWh−1). In particular, even if the solid electrolyte is assumed free, the ASSLBs still cost $134 kWh−1, exceeding the $126 kWh−1 cost for commercial Li-ion batteries. Under these circumstances, the commercial viability of the ASSLBs depends on whether their energy density and safety advantages can justify such high costs in the market, but this cannot be predicted definitively for now. That is, the $50 kg−1 solid-electrolyte cost should by no means be regarded as a threshold guaranteeing an ASSLB cost that is lower than those of commercial Li-ion batteries; instead, it is merely a cost that may yield relatively reasonable ASSLB cost, with potential commercial viability. Additionally, compared with the cost per unit mass like the $50 kg−1 discussed above, the cost per unit volume should be more appropriate for discussing the cost-effectiveness of solid electrolytes. In all-solid-state batteries, the optimal amount of the solid electrolyte is not actually defined by the mass, but by the volume: the composite positive electrode with the optimal tortuosity needs the solid electrolyte to occupy a certain volume fraction, while the balance between energy density and safety is realized by adjusting the thickness of the solid-electrolyte layer. Consequently, no matter what kind of solid electrolyte is employed, the optimal solid-electrolyte volume in each kWh of batteries would be the same. On this basis, as long as the cost per unit volume of the solid electrolyte is determined, the solid-electrolyte cost per kWh of batteries, i.e., the ultimate metric for the cost-effectiveness of solid electrolytes, is determined too. Therefore, compared with the widely discussed cost per unit mass of the solid electrolyte, the cost per unit volume of the solid electrolyte is more suitable for discussion. In the aforementioned study by Pasta et al., the solid electrolyte is assumed to be Li7P3S1159, so, using the density of 1.870 g cm−359 for this material, it can be easily found that the $50 kg−1 gravimetric solid-electrolyte cost that may enable relatively reasonable cell production cost corresponds to a volumetric solid-electrolyte cost of $93.50 L−1.

With this standard clarified, the cost-effectiveness of LZACO may be discussed. The total cost (also referred to as “production cost” in some studies60) of a given solid electrolyte may be obtained by summing its raw materials cost and processing cost. For the LZACO material, both costs can be greatly decreased by replacing Li2O with Li2CO3 in the raw materials for synthesis. On the one hand, Li2CO3 is known to be much cheaper than the moisture-sensitive Li2O. On the other hand, such raw materials replacement is supposed to suppress the processing cost too, as it can effectively reduce the synthesis time: compared with the purchased Li2O, the Li2O in situ formed through Li2CO3 decomposition during intense ball milling would contain a lot more active reaction centers at the surface, thereby enabling faster reaction61. Similar phenomena have also been observed in many other compounds61–63. In particular, given that LZACO is rather O-rich, with the O/Cl molar ratio (0.37) greatly exceeding those of many Li-Zr-Cl-O solid electrolytes such as Li1.75ZrCl4.75O0.5 (O/Cl = 0.11)3, Li2.22Zr1.11Cl5.33O0.67 (O/Cl=0.13)44, and Li3Zr0.75OCl4 (O/Cl=0.25)26, the replacement of Li2O would introduce a relatively large amount of Li2CO3 in the raw materials, making the aforementioned phenomenon especially effective in reducing the synthesis time. This desirable scenario is verified experimentally. With Li2O replaced by Li2CO3 in the raw materials for synthesizing LZACO, the Li2CO3 completely decomposes after only 4-h milling, as indicated by the absence of C signals in the electron energy-loss spectroscopy (EELS) result (Supplementary Fig. 13). More importantly, after such raw material replacement, the ball milling time needed to achieve similar degree of amorphization (Fig. 3a, b) and ionic conductivity (Fig. 3c) reduces drastically from 30 h to merely 4 h; besides, the Li2CO3-synthesized LZACO is even slightly more Li-ion conductive than the Li2O-synthesized one (2.59 vs. 2.55 mS cm−1 at 25 °C), despite the much shorter synthesis time of the former. It should be noted that, among the four components of the processing cost, i.e., instrument depreciation, electricity, plant area, and personnel, most are rather sensitive to the synthesis time, as shown in Fig. 3d (detailed estimation procedure in Methods and Supplementary Tables 1−5). Specifically, the 30-h synthesis time that is rather common among oxychloride solid electrolytes3,47 would in fact give rise to a high processing cost of $63.79 L−1 for LZACO, even after considering its stability in the air with around 4% relative humidity (Supplementary Figs. 14−15). Nevertheless, when the synthesis time is reduced to the 4 h achieved above, the processing cost drops to only $15.31 L−1 (Fig. 3d). In the meantime, since Li2CO3 is also much more affordable than Li2O ($12.64 kg−1 vs. $210.67 kg−1, as shown in Fig. 3e and Supplementary Table 6), the raw materials cost also decreases significantly from $92.97 L−1 to $28.39 L−1. Taking both costs into account, the replacement of Li2O with Li2CO3 decreases the total production cost of LZACO from $156.76 L−1 to $43.70 L−1 (Fig. 3f and Supplementary Table 5), which is much lower than the aforementioned $93.50 L−1 solid-electrolyte cost for enabling reasonable ASSLB cost. Remarkably, this $43.70 L−1 cost for LZACO is also much lower than that of the prototypic Zr-based (oxy)chloride solid electrolyte, Li2ZrCl6; the latter has been commonly regarded as a cost-effective solid electrolyte for long due to its competitive raw materials cost ($30.71 L−1), but, after incorporating the processing cost, its long synthesis time of 45 h47 was found to result in a rather high processing cost of $109.30 L−1 (Fig. 3f and Supplementary Tables 1−5), which alone greatly exceeds the $93.50 L−1 reasonable cost for solid electrolytes (Fig. 3f). Clearly, in order to identify cost-effective, commercially viable solid electrolytes, focusing on the raw materials cost alone is not enough; developing solid electrolytes that may be rapidly synthesized to achieve decent processing cost, such as the LZACO reported here, is equally important.

Although the data above are indicative of decent cost-effectiveness for LZACO, it must also be emphasized that this material alone cannot address the cost issue for the commercialization of ASSLBs. Similar to other Zr-based oxychloride solid electrolytes64, LZACO is not supposed to be compatible with the reductive negative electrodes such as Li metal. Therefore, it may only serve as the catholyte, which still needs to be separated from the negative electrode by the expensive solid electrolytes such as the sulfides3. Besides, the thin Li metal foil needed to enable high energy densities for ASSLBs is also too expensive to make the cost of ASSLBs equal to that of commercial liquid-state batteries58. To endow ASSLBs with commercial viability, the cost of these components must be lowered too. The identification of cost-effective catholytes such as LZACO only meets one necessary but insufficient condition for addressing the cost issue of ASSLBs.

Electrochemical performance
While the observations above have confirmed multiple intriguing properties for LZACO, its comprehensive electrochemical performance may only be verified in all-solid-state cells. Prior to the assembly and testing of cells for this purpose, the electrochemical stability of LZACO was evaluated first. Supplementary Fig. 16 shows the linear sweep voltammetry (LSV) results of the Li | LPSCl-LZACO | LZACO+stainless steel (SS) cell. The data suggest that the reduction and oxidation of LZACO occur at 1.62 and 4.19 V vs. Li/Li+, respectively. The oxidation potential of 4.19 V vs. Li/Li+ is comparable with not only those of sulfide solid electrolytes (no higher than 3 V vs. Li/Li+5,65), but also those of typical Zr-based (oxy)chloride solid electrolytes such as Li2ZrCl6 and Li1.75ZrCl4.75O0.5 (3.55 and 4.00 V vs. Li/Li+, respectively3), so LZACO should supposedly display decent compatibility with the high-potential positive electrodes. Besides, it has been reported that the (oxy)chloride solid electrolytes can generally form stable, Li-ion conductive interphases upon oxidation, which allows for stable cycling to potentials beyond their oxidation limits3,23,66–68. Consequently, the measured oxidation potential of 4.19 V vs. Li/Li+ entails that LZACO may direct contact high-potential positive electrodes such as LiCoO2 and Ni-rich layered oxides in the all-solid-state cell, without the need of any coating layer. On the other hand, the 1.62 V vs. Li/Li+ reduction potential of LZACO is lower than those of typical Zr-based (oxy)chlorides (2.16 and 1.79 V vs. Li/Li+ for Li2ZrCl6 and Li1.75ZrCl4.75O0.5, respectively3), entailing better reduction stability. Regardless, the 1.62 V vs. Li/Li+ reduction potential remains much higher than those of most energy-dense negative electrodes. Furthermore, since the final reduction products of LZACO would inevitably contain electronic conductors such as Zr and Al, which cannot prevent the electrons needed for further reduction to migrate through, the reduction of this material is supposed to proceed continuously69,70. Such speculation is supported by the Li | LZACO | Li and Li-In | LZACO | Li-In symmetric cells, both of which undergo a continuous voltage increase during cycling (Supplementary Fig. 17); in particular, the voltage of the Li | LZACO | Li cell reaches around 2 V after only 80 h of cycling at 0.1 mA cm−2 (1 h per cycle). Therefore, to ensure the stable cycling of the all-solid-state cell, LZACO needs to be separated from the negative electrode by a layer of more negative-electrode-compatible solid electrolyte such as LPSCl.

Based on the electrochemical stability determined above, our study of cell performance focuses on two types of 4 V-class positive electrodes, LiCoO2 (LCO) and scNCM92, with the corresponding cell configurations being Li-In | LPSCl-LZACO | LCO and Li-In | LPSCl-LZACO | scNCM92, respectively. The study begins with the ordinary PEAM mass loading of 5−6 mg cm−2. As shown in Fig. 4a, the Li-In | LPSCl-LZACO | LCO cell with a PEAM mass loading of 5.81 mg cm−2 delivers an initial discharge capacity of 152.6 mAh g−1 and a Coulombic efficiency of 97.26% under 31.6 mA g−1 (0.2 C) at 25 °C; such a discharge capacity is competitive with that of most cells with similar configuration and cycling conditions in literature (usually below 140 mAh g−1; a few examples summarized in Supplementary Table 7)21,23,50,71–73. Besides, thanks to the high ionic conductivity of 2.55 mS cm−1 for LZACO, the cell exhibits decent rate capability too; as shown in Fig. 4b, c, the average discharge capacities at 158, 316, 790, 1106, and 1580 mA g−1 (corresponding to 1 C, 2 C, 5 C, 7 C, and 10 C, respectively) are 139.3, 132.2, 113.6, 94.3, and 69.6 mAh g−1, respectively. Beyond LiCoO2, LZACO also enables decent performance for scNCM92. With a PEAM mass loading of 5.26 mg cm−2, the Li-In | LPSCl-LZACO | scNCM92 cell delivers an initial discharge capacity of 180.8 mAh g−1 and a Coulombic efficiency of 90.27% under 20 mA g−1 (0.1 C) at 25 °C (Fig. 4d), which is also competitive with that of many previously reported all-solid-state cells with the similar configuration and cycling conditions (a few examples shown in Supplementary Table 8). The average discharge capacities at 200, 400, 1000, 1400, and 2000 mA g−1 (corresponding to 1 C, 2 C, 5 C, 7 C, and 10 C, respectively) are 156.3, 141.3, 111.3, 96.5, and 75.5 mAh g−1, respectively (Fig. 4e, f).

More importantly, the mechanically compliant LZACO material can also enable decent long-term cycling stability at high rates. As mentioned above, oxychlorides such as LZACO usually allow for cycling beyond their oxidation potentials, because these materials can form stable and Li-ion conductive interphases upon oxidation3,23,66–68. Under high cycling rates, such a procedure would result in a non-negligible capacity fluctuation during the initial cycles, making it difficult to evaluate the capacity retention. Consequently, these initial cycles (displayed in Supplementary Fig. 18) are treated as formation cycles, and the cycles afterwards are presented as the long-term cycling data in Fig. 4g, h. During such tests, both cells demonstrate satisfactory performance. Under 1580 mA g−1 (10 C) at 25 °C, the Li-In | LPSCl-LZACO | LCO cell with 5.44 mg cm−2 PEAM mass loading shows a capacity retention of 95%, 90%, and 82.06% after 746, 1577, and 2059 cycles, respectively (Fig. 4g). Under 2000 mA g−1 (10 C) at 25 °C, the Li-In | LPSCl-LZACO | scNCM92 cell with 5.62 mg cm−2 PEAM mass loading shows a capacity retention of 95%, 90%, and 80% after 1018, 2776, and 4208 cycles, respectively (Fig. 4h). As shown in Supplementary Tables 9−103,12,16–18,21–25,43,45,49,50,57,71,74,75, among the cost-effective solid electrolytes, LZACO is the only one that can enable stable cycling of the ASSLBs at a rate as high as 10 C, and is also the one that demonstrates the largest number of cycles with the capacity retention above 80% (2059 and 4208 cycles for the Li-In | LPSCl-LZACO | LCO and Li-In | LPSCl-LZACO | scNCM92 cells, respectively). Even when compared with the state-of-the-art but unacceptably expensive solid electrolytes, LZACO still appears rather competitive (Supplementary Tables 9−10). In particular, it needs to be emphasized that the reversible specific capacities of the LZACO-based cells at 10 C is even higher than those of certain cells at 5 C or even 1 C in Supplementary Tables 9−10. Given that the ionic conductivity of 2.55 mS cm−1 at 25 °C for LZACO is not significantly higher than those of other solid electrolytes in Supplementary Tables 9−10, the improved performance of the cells it forms must arise mostly from the high mechanical compliance. With this advantage, LZACO can also enable satisfactory cell performance to the positive-electrode potentials much higher than the commonly used 4.3 V vs. Li/Li+ for testing. As shown in Supplementary Fig. 19, when being cycled between 2.8 and 4.6 V vs. Li/Li+, the Li-In | LPSCl-LZACO | scNCM92 cell with 4.84 mg cm−2 PEAM mass loading displays an initial discharge capacity of 209.58 mAh g−1 and a Coulombic efficiency of 88.16% under 24 mA g−1 (0.1 C) at 25 °C. After 100 cycles under 240 mA g−1 (1 C) at 25 °C, it can still deliver a discharge capacity of 160.3 mAh g−1 with the capacity retention of 89.65%.

In addition to the tests above, the performance of the LZACO-based all-solid-state cells is also evaluated under more practical cycling conditions. It is widely known that the battery-powered instruments usually desire fast charge and relatively slow discharge; for example, the present development of electric vehicles aims at the capability of 3 C−4 C charge, while the discharge rate is usually 0.1−0.3 C, as mentioned in Introduction. Nevertheless, the ASSLBs in literature are rarely cycled under such conditions, but usually operated with the charge and discharge rates being identical. To evaluate the performance of LZACO in this regard, we cycled the Li-In | LPSCl-LZACO | scNCM92 cell with the PEAM mass loading of 5.73 mg cm−2 using the specific currents of 800 mA g−1 (4 C) for charge and 66 mA g−1 (0.33 C) for discharge. The initial cycle under such conditions achieves a discharge capacity of 153.6 mAh g−1 (Fig. 5a), which is not much lower than the cell with both the charge and discharge rates set at 1 C (156.3 mAh g−1, as shown in Fig. 4e, f). On this basis, the cell also exhibits satisfactory cycling stability; the discharge capacity and capacity retention remain above 126.8 mAh g−1 and 80%, respectively, for 231 cycles (Fig. 5b). Beyond the mold cells studied above, we also assembled pouch cells, using the cost-effective dry-film technology. It should be noted that the mechanical compliance for the solid electrolyte has also been found crucial to the fabrication of high-quality films for pouch cells. The compliant solid electrolytes such as the sulfides and halides may easily form and maintain the intimate solid-solid contact with the assistance of the polytetrafluoroethylene (PTFE) binder; instead, if the solid electrolyte is barely compliant like the brittle oxide solid electrolytes, the films cannot enable meaningful cell performance without the addition of minor liquid electrolyte, due to the poor solid-solid contact76. Thanks to the high mechanical compliance of LZACO, the preparation of films for pouch cells are rather convenient. Both the composite positive electrode films and the individual solid-electrolyte films can be easily prepared in relatively large sizes, as shown in Fig. 5c, d and Supplementary Fig. 20. Without the addition of any liquid electrolyte, the Li | LPSCl-LZACO | scNCM92 pouch cell formed by such films demonstrates a reversible capacity of about 160.8 mAh g−1 under 20 mA g−1 (0.1 C) at 30 °C (Fig. 5e).

The data above have demonstrated that LZACO can enable competitive cell performance at 5−10 mg cm−2 PEAM mass loading (equivalent to about 1 mAh cm−2 areal capacity) that is frequently used for testing in literature, but the construction of energy-dense ASSLBs requires higher PEAM loadings above 20 mg cm−2 and larger areal capacities around 4 mAh cm−2. Under such conditions, the volume change would be considerably larger and thus may only be accommodated by highly compliant solid electrolytes. Fortunately, LZACO is rather competent in this regard. When the PEAM mass loadings of the Li-In | LPSCl-LZACO | LCO cell reaches 28.17 mg cm−2, an initial discharge capacity of 149.8 mAh g−1 (equivalent to an areal discharge capacity of 4.22 mAh cm−2) with a Coulombic efficiency of 97.35% may still be achieved under 15.8 mA g−1 (0.1 C) at 25 °C (Fig. 6a). Likewise, the Li-In | LPSCl-LZACO | scNCM92 cell at a similar PEAM mass loading of 25.75 mg cm−2 also delivers a competitive initial discharge capacity of 168.9 mAh g−1 (equivalent to an areal capacity of 4.35 mAh cm−2) with a Coulombic efficiency of 85.06% under 20 mA g−1 (0.1 C) at 25 °C (Fig. 6b). On this basis, the cells with such high PEAM mass loadings demonstrate decent cycling stability. After 100 cycles under the conditions described above, the Li-In | LPSCl-LZACO | LCO and the Li-In | LPSCl-LZACO | scNCM92 cells deliver areal discharge capacities of 3.62 mAh cm−2 (85.78% capacity retention) and 3.92 mAh cm−2 (90.11% capacity retention), respectively. This performance is comparable with the state-of-the-art ASSLBs showing areal discharge capacities around 4 mAh cm−2 in literature, as shown in Supplementary Tables 11, 1212,23,28,77,78. Nevertheless, among the solid electrolytes that can enable such cell performance, LZACO is presently the only one with decent cost-effectiveness38 (Supplementary Tables 11, 12).

While the sulfide- and halide-based all-solid-state cells in literature are usually cycled at high stacking pressures, the LZACO solid electrolyte enables decent cell performance at low stacking pressures as well. The high mechanical compliance of this material allows it to efficiently alter the morphology to accommodate the volume change of the PEAM particles even under limited stresses. If the solid electrolytes employed are all highly compliant like LZACO, the ASSLBs do not have to operate under the impractically high stacking pressures above 100 MPa. In this way, the heavy instrument used to generate such pressures (e.g., the mold used for laboratory testing) is no longer needed, so that the ASSLB may eventually achieve decent energy densities for practical application. To demonstrate the advantage of LZACO for enabling decent low-pressure cell performance, we tried to cycle the Li13Si4 | LPSCl-LZACO | scNCM92 cell under the stacking pressure of 5 MPa. As shown in Fig. 7a, such a cell delivers a discharge capacity of 159.2 mAh g−1 with a Coulombic efficiency of 84.41% at 30 °C and 20 mA g−1 (0.1 C) in the initial cycle. Besides, it also shows satisfactory rate performance; as shown in Fig. 7b, c, the average discharge capacities at 40, 66, 100, 140, and 200 mA g−1 (corresponding to 0.2 C, 0.33 C, 0.5 C, 0.7 C, and 1 C, respectively) are 147.8, 138.3, 128.4, 119.1, and 108.7 mAh g−1, respectively. When cycled between 2.0 and 4.3 V vs. Li/Li+ at 66 mA g−1 and 30 °C, the Li13Si4 | LPSCl-LZACO | scNCM92 cell achieves a capacity retention of 82.06% after 200 cycles under 5 MPa (Fig. 7d). For comparison, we also tried to replace the LZACO in the cells above with Li2ZrCl6 (LZC) or LZCO (both are much less compliant than LZACO, as shown in Fig. 2a), and then conducted the cycling tests under the same conditions, especially the low stacking pressure of 5 MPa. The variation tendency of the cell performance was found consistent with that of the mechanical compliance disclosed in Fig. 2a. As shown in Supplementary Fig. 21, the least compliant LZC solid electrolyte results in the poorest cycling performance; the capacity retention after 100 cycles is only 51.09%. In comparison, the relatively more compliant LZCO enables better cycling stability, with the capacity retention being 69.21% after 100 cycles. As for LZACO, its mechanical compliance greatly exceeds those of both LZC and LZCO (Fig. 2a), so this material enables the most stable cycling performance; after 100 cycles, the capacity retention is 91.52%. In addition to the two typical Zr-based (oxy)chloride solid electrolytes for comparison above, the mechanically compliant LZACO can also enable improved cell performance than many other widely studied solid electrolytes. As shown in Supplementary Table 13, the cycling performance achieved by the LZACO-based cells at 5 MPa is comparable with that of certain cells at higher pressures such as 10 MPa11,35,79. These observations demonstrate the advantage of the mechanically compliant LZACO in enabling decent cell performance at low stacking pressures, which is a prerequisite for constructing practical ASSLBs. Furthermore, it should also be noted that the low-pressure cell performance achieved here still has very large room for improvement, because, due to the poor reduction stability of LZACO (reduction potential 1.62 V vs. Li/Li+, as shown in Supplementary Fig. 16), the anolyte of the cell above is still the commonly used LPSCl, which is much less compliant than LZACO (as shown in Fig. 2a) and thus unlikely to perform well at low stacking pressures. If an negative-electrode-compatible solid electrolyte that is as compliant as LZACO can be developed in the future, the low-pressure cell performance similar to those at high stacking pressures should be achievable. To this end, the interphase resulting from the reduction of the solid electrolyte must be electron-blocking, so that the electrons needed for further reduction cannot migrate through to reach the unreacted solid electrolyte80. Considering that the Zr4+ and Al3+ in LZACO would inevitably be reduced into electronic conductors such as Zr and Al by Li metal81,82, the presence of such metal cations should preferably be eliminated in the material. Instead, the solid electrolyte needs to be populated by non-metal cations such as P5+ and B3+, which will only be reduced into electron-blocking species80. If desirable mechanical compliance and ionic conductivity can be realized in such materials through rational materials design too, the cost-effective ASSLBs that can operate at sufficiently low stacking pressures for practical application may be expected.

In addition to the decent cell performance, the data above also demonstrate one crucial point: the importance of the mechanical compliance for solid electrolytes. In the discussion above, the all-solid-state cells formed by LZACO are compared with those based on other solid electrolytes when different PEAMs, PEAM mass loadings, cycling conditions, etc., are employed (Supplementary Tables 7−13). Among all the solid electrolytes involved in such comparison, LZACO is in fact not the one with the highest ionic conductivity. Regardless, the cell constructed by LZACO can still display improved performance with respect to those based on other more Li-ion conductive solid electrolytes. The improved mechanical compliance of LZACO (0.22 GPa hardness and 1.41 GPa Young’s modulus, as shown in Fig. 2a) plays a pivotal role here. In fact, when the ionic conductivity of the solid electrolyte exceeds 1 mS cm−1, improving its mechanical compliance should be more effective in optimizing the cell performance than further increasing the ionic conductivity, as the bottleneck of the overall ion transport has shifted from the interior of the solid electrolyte to the interfacial contact between different cell components. Under such circumstances, if the cell employs highly compliant solid electrolytes such as LZACO, it can more easily achieve and maintain the intimate solid-solid contact, thereby effectively improving the overall ion transport efficiency. From this perspective, the report of the mechanically compliant LZACO has pointed out an effective entry point for further optimizing the comprehensive performance of the solid electrolytes that are already highly Li-ion conductive.

Discussion
In summary, by designing and synthesizing the solid electrolyte LZACO, we achieve a mechanical compliance improving those of most previously reported inorganic solid electrolytes (hardness: 0.22 vs. >1 GPa; Young’s modulus: 1.41 vs. >15 GPa), as well as a high Li-ion conductivity (2.55 mS cm−1 at 25 °C) and a strong cost-competitiveness (estimated to be $43.70 L−1, below the $93.50 L−1 solid-electrolyte cost for enabling relatively reasonable cell production cost38). The combination of such high mechanical compliance and Li-ion conductivity enables cell performance comparable to those of the cells formed by state-of-the-art but unacceptably expensive solid electrolytes. With the ordinary PEAM mass loading of 5−6 mg cm−2, the LZACO-based cells with LCO and scNCM92 deliver initial discharge capacities of 152.6 and 180.8 mAh g−1 under 0.2 C and 0.1 C, respectively, at 25 °C; under 10 C at 25 °C, these two cells show capacity retentions of 82.06% after 2059 cycles and 80% after 4208 cycles, respectively. When being cycled under conditions closer to practical situations, such as 4 C charge and 0.33 C discharge at 25 °C, the scNCM92 cell exhibits an initial discharge capacity of 153.6 mAh g−1, and sustains the capacity retention above 80% for 231 cycles. More importantly, decent performance was also achieved with the PEAM mass loading above 20 mg cm−2. After 100 cycles under 0.1 C at 25 °C, the cell with the LCO mass loading of 28.17 mg cm−2 demonstrates an areal discharge capacity of 3.62 mAh cm−2 with 85.78% capacity retention, while the cell with the scNCM92 mass loading of 25.75 mg cm−2 demonstrates an areal discharge capacity of 3.92 mAh cm−2 with 90.11% capacity retention. Considering that the LZACO material enabling such cell performance also shows a reasonable cost as mentioned above38, it could potentially become a suitable solid electrolyte for the commercial, practical ASSLBs in the future.

Methods
Materials synthesis
The xLi2O-(1-y)ZrCl4-yAlCl3 solid electrolytes were synthesized mechanochemically by milling the stoichiometric amount of Li2O (Aladdin, 99.99%) or Li2CO3 (Sigma-Aldrich, 99.997%), ZrCl4 (Acros Organics BVBA, 98%), and AlCl3 (Alfa Aesar, 99%) with zirconia balls (5 mm diameter) at a ball-to-powder mass ratio of 20:1 (the mass of the balls is 40 g in each pot) in 80 ml zirconia pots using a planetary mill (FRITSCH, Pulverisette 7 premium line). The milling was conducted at 500 rpm, for the different durations specified in the main text. The Li1.75ZrCl4.75O0.5 solid electrolyte for comparison was synthesized using the same method and instrument from LiCl (Alfa Aesar, 99.9%), Li2O (Aladdin, 99.99%), and ZrCl4 (Acros Organics BVBA, 98%), with the ball-to-powder mass ratio, mass of the balls in each pot, milling speed, and milling time being 15:1, 30 g, 600 rpm, and 40 h, respectively. For all the mechanochemical syntheses, the milling was stopped for 6 min after every 6 min of milling. During the entire procedure, the materials were handled in an Ar-filled glovebox with H2O and O2 contents both below 0.01 ppm, while the planetary mill was also conducted with the pots sealed to prevent air exposure. Unless otherwise specified, the Li source for all the xLi2O-(1-y)ZrCl4-yAlCl3 solid electrolytes in the presented study is Li2O. For the xLi2O-(1-y)ZrCl4-yAlCl3 solid electrolytes synthesized using Li2CO3 as the Li source, the absence of C in the product is verified by electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM) from at least 30 different regions in the sample. Although each individual EELS measurement only collects information from a rather local region of nanometer size, in such a region EELS could detect the minor amount of C species that is invisible in other macroscopic characterization techniques such as X-ray photoelectron spectroscopy (XPS). Since such highly sensitive characterization did not detect the existence of any C in at least 30 different regions in the sample as mentioned above, it should be safe to conclude that the amount of C is negligibly small.

Structure and morphology characterizations
X-ray diffraction (XRD) experiments were conducted on a Rigaku Ultima IV powder X-ray diffractometer operating at 40 kV and 40 mA with a scanning step of 0.02° and scanning speed of 2° min–1, using Cu Kα1 radiation (λ=1.5406 Å). During the measurement, Kapton films were used to prevent the sample from being exposed to air. The neutron total scattering experiment for the determination of the pair distribution function (PDF) was conducted on the Multi-Physics Instrument (MPI) at the China Spallation Neutron Source (CSNS)83. For each measurement, approximately 1.5 grams of the solid-electrolyte powder was sealed in a cylindrical vanadium nickel alloy container under a helium gas atmosphere. The acquired total neutron scattering datasets of PDFs with a maximum momentum transfer Qmax = 31.5 Å−1 were obtained through the Mantid software84 and Fourier transformation. The simulation of the PDFs was conducted using the PDFgui software85. The scanning electron microscopy (SEM) observation was conducted using a ZEISS GeminiSEM 500 scanning electron microscope operated at 3 kV. The density of the solid electrolyte was calculated from the density of its cold-pressed pellet and the relative density of this pellet; the latter was determined by averaging the relative densities of at least 30 regions of the cold-pressed pellet (the relative density of each region is determined from the SEM image using the Adjust-Threshold plugin of ImageJ51). The focused-ion beam (FIB) sectioning of the composite positive electrodes of the cycled all-solid-state cells were performed at 30 kV and 15 nA using a ThermoFisher Helios G4 Plasma-FIB instrument. For both the SEM and FIB experiments, the samples were transferred by air-tight transfer holders to avoid exposure to air. The high-resolution transmission electron microscopy (HRTEM) observation was conducted on powder samples using a JEOL JEM-F200 microscope operated at 200 kV. To suppress the electron-beam irradiation damage, the observation was conducted using a cryogenic TEM holder (which will also prevent air exposure during specimen transfer) at −170 °C. The electron energy-loss spectroscopy (EELS) measurement was conducted on powder samples in a ThermoFisher Scientific Titan ETEM G2 TEM operated at 300 kV using a cryogenic TEM holder, which ensures both the absence of air exposure during specimen transfer and an observation temperature of −170 °C (for the suppression of electron-beam irradiation damage). The EELS data were collected in the scanning transmission electron microscopy mode using a Gatan Image Filter Quantum-965 spectrometer, where a 5 mm aperture and an energy dispersion of 0.5 eV per channel were adopted.

Mechanical characterizations
The mechanical characterizations in the present study were all conducted on the pellets formed by cold pressing the solid-electrolyte powder at 300 MPa. The hardness of the solid electrolyte was measured by conducting nanoindentation within SEM using the Hysitron PI 88 in situ nanoindenter with a Berkovich tip under a high load regime. The samples were transferred into the SEM by an air-tight transfer holder to avoid air exposure. The hardness was calculated from the unloading curve using the method developed by Oliver and Pharr86,87. The Young’s modulus of the solid electrolyte was measured by atomic force microscopy (AFM) in peak force quantitative nanomechanical mapping mode and analyzed by Derjaguin-Muller-Toporov model. The AFM tip (RTESPA-300) is made of Sb-doped Si; it shows the rectangular geometry, a radius of 8 nm, and a spring constant of 40 N m−1. The AFM instrument was placed in an Ar-filled glovebox with H2O and O2 contents both below 0.01 ppm.

Phase-field modelling
The simulation of the interfacial cracking between the solid-electrolyte layer and the composite positive electrode layer is based upon the model described schematically in Supplementary Fig. 22; the PEAM in such simulation is the single crystalline LiNi0.92Co0.06Mn0.02O2 (scNCM92), and the solid-electrolyte material is either Li1.75ZrCl4.75O0.5 (LZCO) or 1.4Li2O-0.75ZrCl4-0.25AlCl3 (LZACO). Considering that the property of the interface differs from that of the bulk, an interface layer was introduced between the solid-electrolyte layer and the composite positive electrode layer, and a pre-existing notch was added to initiate the crack development. In the phase-field simulation, the cracking at the interface was analyzed by coupling an order parameter ϕ, representing damage which in a continuous manner separates detachment (ϕ=1) from intact (ϕ=0), with the boundary value problem of continuum mechanics. Since the current rate is only 0.1 C in the experiment, a quasi-static degradation model based on a previous study88 and controlled by the shrinkage deformation of scNCM92 was used for the analysis. The simulation was conducted in COMSOL, based upon the material parameters indicated in Supplementary Table 14.

Cost analysis
The production cost of the solid electrolyte is estimated by summing its raw materials cost and processing cost. The raw materials cost per unit volume of the solid electrolyte is calculated by multiplying the cost per unit mass of the solid electrolyte and the density of the solid electrolyte. While the method of density measurement has already been described in the “Structure and morphology characterizations” section above, the cost per unit mass of the solid electrolyte was calculated straightforwardly from the average market prices of the corresponding raw materials as the industrial commodity chemicals in the year 2024. These prices and the information sources are listed in Supplementary Table 6. To estimate the processing cost, we assume the solid-electrolyte production to take place in a walk-in enclosure with 3×20 m2 area and 2.5 m height (Vigor Gas Purification Technologies Co., Ltd.), within which the relative humidity is maintained at 4% and 28 industrial planetary mills (XQM-12T, Changsha Tianchuang Powder Technology Co., Ltd.) are used to fabricate the solid electrolyte. These industrial planetary mills can produce 28 kg of solid electrolyte per batch. Therefore, dividing the processing cost per batch of production by 28 kg and then multiplying the result by the density of the solid electrolyte would yield the processing cost per unit volume of the solid electrolyte. The processing cost per batch of production that is needed for this calculation consists of four components: instrument depreciation cost, electricity cost, personnel cost, and plant area cost. The depreciation cost of each instrument was calculated via dividing its price by the depreciation period (acquired from the manufacturer) and multiplying the result by the working time of this instrument during each batch of production. The electricity cost of each instrument was calculated from the average industrial electricity price for China in September 2025, the rated power of this instrument, and the time it operates at the rated power. For the planetary mill, since it needs to be operated intermittently (such as 5-min milling followed by 5-min break for cooling), the working time for depreciation cost estimation is considered twice the effective milling time for electricity cost estimation. The personnel cost was calculated from the time needed for operating each instrument and the average salaries of battery industry in China reported in January, 202558. The plant area cost was estimated from the time needed for each batch of production, the area of the aforementioned walk-in enclosure, and the industrial facility rent in China, which was obtained by averaging the rents of 30 industrial parks located in different cities in September 2025.

Humidity tolerance test
The humidity tolerance test was conducted by placing 0.3 g loose powder of the solid electrolyte either within an environmental chamber (Shanghai Duohe Instrument, DHTSLH-27-O-AR-SD) or a dry room filled with dry air of 4% relative humidity at 25 °C for 12 h. Afterwards, the XRD and EIS tests were conducted on the exposed powder and the 300 MPa-cold-pressed pellet of the exposed powder, respectively, at 25 °C. The data were then compared with those of the non-exposed solid electrolyte.

Conductivity measurements
The ionic and electronic conductivities were both measured using pellets prepared by cold pressing the solid-electrolyte powder at 300 MPa for 1 min, and this pressure was maintained during the measurement as well. The ionic conductivity was measured by electrochemical impedance spectroscopy (EIS) with two stainless steel rods as the blocking electrodes, using a Bio-Logic MTZ-35 impedance analyzer with an amplitude of 10 mV and frequency range of 35 MHz to 1 Hz. The applied signal is potentiostatic. Each Nyquist plot collected in this condition consists of 35−45 data points. No quasi-stationary potential or current was applied prior to measurement. The electronic conductivity was determined by the direct-current (DC) polarization measurements using CH Instruments CHI630E electrochemical analyzer with the applied voltage of 1 V.

Linear sweep voltammetry (LSV) measurements
To assemble the cell for LSV measurements, 60 mg of the 1.4Li2O-0.75ZrCl4-0.25AlCl3 powder was first cold-pressed at 150 MPa for 1 min in the mold with 10 mm diameter, and then 60 mg of Li6PS5Cl powder (Shenzhen Kejing Star Technology) was pressed on one side of the 1.4Li2O-0.75ZrCl4-0.25AlCl3 layer under 150 MPa for 1 min; the final thicknesses of these two solid-electrolyte layers are around 280 and 375 μm, respectively. Afterwards, 20 mg of the mixture of 1.4Li2O-0.75ZrCl4-0.25AlCl3 and 304L stainless-steel (SS) powders with the weight ratio of 1:3 was uniformly sprinkled on the other side of the 1.4Li2O-0.75ZrCl4-0.25AlCl3 layer and pressed at 300 MPa for 3 min. Finally, a piece of fresh Li metal foil (100 μm thick, Tianjin Energy Lithium Co., LTD) was attached to the Li6PS5Cl layer. The LSV measurements were conducted using a CH Instruments CHI630E electrochemical analyzer with a scan rate of 0.1 mV s−1 under an external pressure of 10 MPa at 25 °C.

Assembly and tests of all-solid-state cells
The positive electrode active material (PEAM) powders, i.e., single crystalline LiNi0.92Co0.06Mn0.02O2 (scNCM92; Minmetals New Energy Materials Co., LTD) and LiCoO2 (LCO; Guangdong Canrd New Energy Technology Co., LTD.), were dried at 100 °C in a drying oven for 10 h before use. The composite positive electrodes were prepared by firstly mixing the PEAM and the oxychloride solid-electrolyte powders at a weight ratio of 75:25 in an agate mortar for 30 min, and then in a vortex mixer (Haimen Kylin-Bell Lab Instruments, QL-866) for 10 min at 1200 rpm. The preparation of the Li-In alloy negative electrode will be described below, along with the cell assembly procedure. The composite negative electrode based on Li13Si4 was prepared by mixing the Li13Si4 (Onstar New Carbon Materials Changzhou Co., LTD.) and the Li6PS5Cl (Shenzhen Kejing Star Technology Company) powders at a weight ratio of 60:40 in an agate mortar for 20 min. The assembly of the mold cells began with pressing 25 mg of the oxychloride solid-electrolyte powder at 150 MPa for 1 min in a mold with 10 mm diameter (final thickness around 115 μm). Subsequently, the composite positive electrode powder was uniformly spread onto one side of the cold-pressed oxychloride solid-electrolyte layer and pressed under 300 MPa for 3 min. To avoid reaction between the oxychloride solid electrolyte and the negative electrode, 35 mg of Li6PS5Cl powder was pressed on the other side of the oxychloride solid-electrolyte layer at 150 MPa for 1 min (final thickness around 220 μm). For the cells with the Li-In alloy negative electrode, a piece of indium foil (100 μm thick, Alfa Aesar) was then placed on top of the Li6PS5Cl layer, followed by the attachment of a piece of fresh Li metal foil (50 μm thick, Tianjin Energy Lithium Co., LTD). For the cells with the Li13Si4 negative electrode, 25 mg of the aforementioned composite negative electrode, i.e., the one prepared by mixing Li13Si4 and Li6PS5Cl powders, was pressed at the surface of the Li6PS5Cl layer under 100 MPa for 1 min. The all-solid-state cell formed this way was sandwiched between two stainless-steel rods as current collectors. Finally, the stacking pressure (specified in the figure captions for each cell discussed) was applied to the cell and maintained during the cycling tests. The assembly of the all-solid-state pouch cells began with preparing the composite-positive-electrode and solid-electrolyte sheets by the dry-film processing method. Specifically, 0.5 wt% polytetrafluoroethylene (PTFE; number-average molecular weight 7700 kg mol−1, Guangdong Canrd New Energy Technology Co., LTD.) was mixed with the aforementioned composite-positive-electrode or solid-electrolyte powders to form doughs, and then the doughs were calendared to the desired thickness (~70 and ~80 um for the composite-positive-electrode and solid-electrolyte sheets, respectively). Afterwards, the composite-positive-electrode sheet, 1.4Li2O-0.75ZrCl4-0.25AlCl3 sheet, Li6PS5Cl sheet, and Li metal foil (50 μm thick, Tianjin Energy Lithium Co. LTD) were stacked and packed into a laminate bag. After applying a vacuum to the laminate bag, it was sealed and pressed at 10 MPa (this pressure was maintained during cycling tests too). All the cell fabrication processes were carried out in an Ar-filled glovebox with H2O and O2 contents both below 0.01 ppm. The cycling tests were conducted using the Neware CT-3000N and LAND CT2001A battery testing systems. The temperature during the cycling tests was maintained using an incubator (Tianjin Hongnuo Instrument, SPX-250B, temperature accuracy ±1 °C). Prior to the tests, all the cells were placed in the incubator for 5 h to reach thermal equilibrium at the target temperatures. To ensure reproducibility, at least ten cells were tested for each electrochemical experiment, and the one with the performance closest to the average among these cells is selected for display in the figures.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript addresses the importance of plastic deformation in solid electrolytes for all-solid-state batteries. It reports the discovery of a Li-Al-Zr-Cl-O composition that exhibits not only high ionic conductivity with relatively low raw material costs but also an exceptionally low hardness of 0.22 GPa. This hardness is significantly lower than that of other solid electrolytes previously considered compliant materials. While individual properties of the Li-Al-Cl-O and Li-Zr-Cl-O material classes have been reported previously and are not entirely novel, this manuscript provides helpful clarification by demonstrating that these desirable characteristics can be simultaneously achieved by combining these two material classes.\nAlthough this finding is valuable, the materials characterization presented in the manuscript is relatively weak, despite the work focusing on the identification of a specific composition within an already known material system. In this regard, I believe the manuscript has the potential to be published in Nature Communications after addressing the following major concerns.\nMajor Points for Revision\n(1) Clarification on Mixed-Anion Materials and Mechanical Properties (Page 6):\nThe authors state that “materials with two types of anions are usually much more compliant than those with only one.” This statement is misleading, as \"softness\" is not a general characteristic of mixed-anion materials. Mechanical properties are primarily determined by bonding nature within specific crystal structures or local atomic arrangements, not simply by the presence of multiple anions. The authors should clarify the specific mechanisms or structural features by which anion mixing leads to enhanced compliance in this system.\n(2) Misleading Analysis of Amorphous and Crystalline Phases:\ni) XRD Interpretation (Figure 1d, 1e, and Supplementary Figures):\nThe small peaks observed in the XRD patterns are attributed to either P3m1 or C2/m space groups. The manuscript presents this as though portions of LZACO crystallize in these specific phases. However, these peaks correspond to characteristic reflections of fcc or hcp anion packing (e.g., LiCl typically exhibits fcc anion packing). The C2/m and P3m1 structures in this material class are part of these broader anion packing frameworks. It is therefore an overstatement to attribute these peaks definitively to C2/m or P3m1 space groups without further evidence.\nii) Precipitation vs. Allotropes in XRD Observations:\nThe XRD peaks observed are more likely due to the precipitation of Li-(Al, Zr)-Cl phases rather than crystalline forms of the oxychloride. This suggests segregation of stable phases from a metastable amorphous matrix. However, the authors suggest that the oxychloride phase itself consists of crystalline and amorphous regions, which is not convincingly supported by the data. If the authors contend that these crystalline phases are allotropes of the oxychloride, additional supporting evidence should be provided.\niii) PDF Analysis (Supplementary Figure 4):\nThe pair distribution functon(PDF) analysis shows distinct peaks extending to long radial distances, which is characteristic of crystalline rather than amorphous materials. While radial distribution functon(RDF) peaks can sometimes result from artifacts in the Fourier transform process, the current interpretation of the PDF data is misleading. The authors should revise their interpretation or reanalyze the data to avoid misinforming readers.\niv) TEM/FFT Analysis (Supplementary Figure 5):\nThe interpretation of the TEM and FFT patterns in Supplementary Figure 5 appears inconsistent. If the two spots observed in the FFT pattern (Figure 5b) represent a crystalline feature, they suggest a single crystal orientation. However, the regions claimed to be crystalline in the TEM image in Figure 5d are scattered , which should result in a ring-like FFT pattern, not discrete spots. This inconsistency needs to be addressed, as it undermines the interpretation of the sample’s microstructure.\n(3) Nanoindentation Data Interpretation (Figure 2a):\nFigure 2a presents the Young’s modulus and hardness of various materials measured by nanoindentation on cold-pressed pellets using a Berkovich tip. While nanoindentation is a well-established method, accurate measurements require samples with surfaces flat relative to the tip radius and near-full densification (≈100% density). Cold-pressed pellets often do not meet these criteria. Therefore, the manuscript should include surface micrographs and representative load-displacement (or stress-strain) curves for each measurement, rather than reporting only final values. This additional data would substantiate the reliability of the mechanical measurements.\n(4) Comparison with Li-Al-Cl-O Reference Data:\nPrevious studies have already demonstrated that Li-Al-Cl-O materials are exceptionally compliant compared to other chloride-based solid electrolytes. Thus, it is important for the authors to contextualize the mechanical properties of LZACO by comparing them directly with both Li-Zr-Cl-O and Li-Al-Cl-O. While data for Li-Zr-Cl-O is included in Figure 2a, comparable data for Li-Al-Cl-O—arguably a more relevant benchmark—is missing. The authors should provide nanoindentation results for Li-Al-Cl-O in Figure 2a for a more comprehensive comparison.\n(5) Battery Performance and SEM Analysis (Figures 2c and 2e):\nThe cycling performance of the battery incorporating LZCO (Figure 2c) appears significantly poorer than comparable data for chloride or oxychloride electrolytes in the literature. This could mislead readers regarding the material’s true potential. Moreover, the SEM image in Figure 2e reveals an excessive volume of voids. If these voids result from the volume change of cathode materials, then the entire cathode layer thickness should expand proportionally, which is not evident. It is more likely that these voids were present prior to battery assembly, suggesting poor electrode fabrication. This fabrication issue could account for the poor electrochemical performance shown in Figure 2c. The authors should clarify this point and, if applicable, improve their cell assembly to better represent the intrinsic properties of the electrolyte.\nSummary\nThe manuscript presents an important advancement in the design of compliant solid electrolytes for all-solid-state batteries. However, substantial revisions are required to strengthen the materials characterization, clarify data interpretation, and ensure the reliability of the reported findings. Addressing the points above will significantly enhance the manuscript’s clarity, rigor, and impact, making it suitable for publication in Nature Communications.", "reviewer_2": "I believe this manuscript will make a significant contribution to the solid state battery field, presenting a low cost solid state electrolyte for dry and wet process of fabrication cells with high nickel content. The authors' approach integrates this research from lab scale to large scale application – pouch cell. To enhance clarity and support the authors' claims, the following points should be considered:\n1. Please consider about the title associated with the work, because the work is related to the low cost of materials and solid state battery, examples below. I believe that you have opinions and understanding which title is better for your work.\n- Cost-Effective and Mechanically Compliant LZACO: Advancing All-Solid-State Li Batteries,\n- Enhancing All-Solid-State Li Battery Performance with LZACO: A New Standard in Electrolytes,\n- LZACO Solid Electrolyte: Achieving High Performance and Commercial Viability in Li Batteries.\n2. How does the mechanical compliance of LZACO compare to other solid electrolytes in practical applications? What specific tests or methods were used to measure the hardness and Young’s modulus of LZACO?\n3. The cost-effectiveness of LZACO with a raw materials cost of $10.61/kg. How was this cost calculated, and what factors contribute to its competitiveness? Are there any potential fluctuations in raw material prices that could affect the cost-effectiveness of LZACO?\n4. What is the environmental impact of producing and using LZACO, considering both the raw materials and the manufacturing process?\n5. What future research directions or improvements are suggested by the authors to further enhance the performance and applicability of LZACO? Are there any potential barriers to further development and commercialization that need to be addressed?\n6. Phase-field modeling to compare LZACO and LZCO. How do the computational results align with the experimental findings, and what insights do they provide about the mechanical compliance of LZACO? What specific experimental setups and conditions were used to validate the computational results, and how do these setups ensure the reliability of the findings?\n7. The cycling performance of cells using LZACO and LZCO. How does the mechanical compliance of LZACO contribute to its superior cycling performance compared to LZCO? What are the implications of the observed differences in cycling performance for the practical application of LZACO in all-solid-state batteries?\n8. The impact of volume change in the composite cathode layer on the cycling stability. How does the mechanical compliance of LZACO help in accommodating these volume changes, and what advantages does this offer for long-term stability? How do the experimental conditions (e.g., CAM mass loading, cycling rate) affect the observed performance, and what considerations should be taken into account for practical applications?\n9. Li2O can be replaced by the cheaper Li2CO3 in the synthesis of LZACO. How does this substitution impact the overall cost and quality of the solid electrolyte? What methods were used to confirm the complete decomposition of Li2CO3 during the synthesis process, and how reliable are these methods?\n10. the structural and ionic conductivity similarities between LZACO synthesized using Li2O and Li2CO3. How do the XRD and EELS data support these findings, and what implications do they have for the practical application of LZACO? How does the ionic conductivity of LZACO synthesized using Li2CO3 compare to other solid electrolytes, and what factors contribute to its high performance?\n11. the potential competitiveness of LZACO in terms of production cost due to its stability in humid air. How does this stability compare to other solid electrolytes, and what advantages does it offer for large-scale production? What specific measures or conditions are required to maintain the stability of LZACO during handling and storage, and how do these measures impact the overall production cost?\n12. The reduction and oxidation potentials of LZACO. How do these potentials compare to other solid electrolytes, and what implications do they have for the stability and performance of LZACO in all-solid-state cells?\n13. The performance of cells with LiCoO2 and scNCM92 cathodes. How do the initial discharge capacities and Coulombic efficiencies of these cells compare to those reported in the literature for similar configurations?\n14. LZACO is the only solid electrolyte with sufficiently low cost for commercialization that can enable stable cycling at a rate as high as 10 C. How was this cost-effectiveness determined, and what factors contribute to its competitiveness compared to other solid electrolytes?\n15. The performance of LZACO-based pouch cells. How do the mechanical properties of LZACO contribute to the fabrication and performance of these pouch cells?\n16. The performance of LZACO-based cells at low stacking pressures. How does the mechanical compliance of LZACO enable decent performance under these conditions, and what advantages does this offer for practical applications? What potential improvements could be made to further enhance the low-pressure cell performance, and how might these improvements impact the overall usability of LZACO?", "reviewer_3": "This paper reports Li2O-ZrCl4-AlCl3 solid electrolytes exhibiting ionic conductivity of ~2.2 mS/cm and its cost-effective synthesis using Li2CO3 as a precursor. ASSBs using these solid electrolytes as the catholyte are demonstrated. The finding is technically important, however, the novelty of this work is not enough to satisfy the high standard of Nat. Commun. Rather this work is worth to be reported in other more specialized journals.\nAs for novelty, many oxy-halide SEs exhibiting mS/cm-class ionic conductivity have been reported (e.g. LiNbOCl4, LiAlCl2.5O0.75, many Li-Zr-Cl-O compounds, xLi2O-MCly (M = Ta, Hf)) while many of those previous reports already highlighted the role of amorphous matrix for achieving high ionic conductivity. Compare to the previous papers on oxy-halide SEs, this work does not provide new scientific insights in terms of material characterization, structure-property relation, or performances.\nThe change of XRD patterns of LZACO after annealing should be discussed in detail. After 100 oC annealing, it seems to transform to the trigonal structure than it decomposed with the appearance of LiCl?\nIt is recommended to examine air- and dry-room stability of LZACO to estimate its availability in a practical cell manufacturing process.", "reviewer_4": "This study emphasizes the critical role of mechanical compliance in solid electrolytes for all-solid-state batteries, alongside ionic conductivity and cost. In this regard, the authors introduces xLi2O-(1-y)ZrCl4-yAlCl3 (LZACO, x = 1.0 ~ 1.8, y = 0.2 ~ 0.5) as a novel oxychloride electrolyte with remarkably low hardness (0.22 GPa) and Young’s modulus (1.41 GPa), targeting commercialization viability. LZACO is synthesized via mechanochemical milling of Li2CO3, ZrCl4, and AlCl3, achieving an ionic conductivity of 2.55 mS cm−1 at 25°C through amorphous-phase dominance. The authors estimated that the cost of raw material is using a log-log scaling model, with Li2CO3 replacing costly Li2O. Given the result from cost modeling, the authors suggest the low cost of raw material of $10.61 kg−1 for LZACO by substituting Zr4+ and Al3+ for Ta5+ from 1.6Li2O-TaCl5 and replacing Li2O to Li2CO3 for synthesis. The synthesized LZACO exhibits superior deformability compared to sulfide/halide electrolytes and the phase-field modeling further supports the important of low hardness and Young’s modulus. The authors demonstrated the effect of improved mechanical compliance of LZACO by showing long term cycling of all-solid-state batteries using LiCoO2 and NCM92 cathodes achieving 3.62–3.92 mAh cm−2 areal capacity (85–90% retention after 100 cycles) at 25°C. While the authors demonstrate the excellent electrochemical properties of LZACO in all solid state batteries (ASSBs), I believe this paper ultimately falls short of the requirements for publication in nature communications for the reasons articulated below.\n1. Page 6, line 2: The authors propose a chemical price threshold of $50 kg⁻¹ for the commercialization of ASSBs. However, this paper provides no supporting evidence for this value, nor do the references cited offer any justification. To substantiate this claim, the authors should present a comprehensive market analysis, including data from at least the past two years, as well as a universal framework for estimating the chemical cost associated with ASSB commercialization.\n2. Supplementary table 1 and 2: The authors present laboratory-scale chemical prices for solid electrolyte fabrication in Supplementary Tables 1 and 2. However, these prices are derived solely from two chemical suppliers, Alfa Aesar and Aladdin, and are limited to data from January 2025. Relying on arbitrarily selected suppliers over such a narrow timeframe undermines the credibility of the economic and scientific analysis. A broader dataset encompassing multiple suppliers and a longer time period is necessary to provide a robust evaluation.\n3. In addition to the chemical cost of solid electrolytes, the overall price of ASSBs is influenced by various hidden manufacturing expenses, such as synthesis processing fees, chemical maintenance costs, and others. Moreover, material costs can fluctuate significantly during mass production for commercialization. Importantly, LZACO requires co-utilization with sulfide-based solid electrolytes or Li-alloy anodes due to its incompatibility with Li metal anodes, which reduces the energy density of ASSBs and increases manufacturing costs. Consequently, laboratory-scale chemical pricing alone is insufficient to convincingly demonstrate LZACO's advantages for ASSB commercialization.\n4. Page 9, line 3-16: The authors attribute LZACO's high ionic conductivity to material amorphization, referencing studies on Zr-based halide solid electrolytes. While \"intermediate compositions\" have been reported in prior research in references, the correlation between these compositions, amorphous phases in synthesized materials, and their impact on ionic conductivity remains unclear. As ball milling-induced amorphization introduces atomic site disorder within materials, this phenomenon should be thoroughly discussed in relation to its influence on LZACO's ion conductivity.\n5. The synthesis of amorphized Li₂ZrCl₆ solid electrolytes via anion substitution (e.g., Cl⁻ replaced by other anions) has already been extensively explored in previous studies (e.g., J. Cheng et al., Journal of Energy Storage, 2024, 89, 111700, D. Xu et al., J. Mater. Chem. A, 2024, 12, 27694, F. Hussain et al., npj Comput Mater, 2024, 10, 148, and etc.). Similarly, substituting Zr with Ta has been reported (e.g., X. Liu et al., Energy Storage Materials, 2024, 72, 103737 and etc.). Furthermore, the economic evaluation of oxyhalide solid electrolytes was addressed in earlier work (L. Hu, Nat Commun., 2023, 14, 3807). While this paper provides additional insights into LZACO's mechanical properties, its lack of novelty regarding the material itself diminishes its overall contribution to the field.\n6. The authors highlight the low Young’s modulus and hardness of LZACO as critical factors for stable contact between LZACO and cathode active materials during ASSB cycling. However, their experiments employed an impractically high stack pressure of 190 MPa with low cathode active material loading of ~5.5 mg‧cm⁻², which fails to substantiate the mechanical compliance benefits of LZACO under realistic conditions. Furthermore, Figures 6 and 7 show that LZACO cells with high cathode loading of > 25 mg‧cm⁻² cycled at low stack pressure of 5 MPa do not outperform previously reported oxyhalide solid electrolytes in ASSBs in terms of capacity retention. A systematic comparison of stack pressure effects on ASSB cycling using LZACO versus other solid electrolytes such as LZCO or LZO would provide more compelling evidence for the importance of mechanical compliance."}, "author_response": "Responses to Reviewers’ Comments\nUnless otherwise specified, all page numbers, figure numbers, and reference numbers mentioned\nbelow refer to the numbering sequence in the revised manuscript.\nThe contents copied from the revised manuscript are highlighted in yellow.\nReviewers' comments:\nReviewer #1 (Remarks to the Author):\nThis manuscript addresses the importance of plastic deformation in solid electrolytes for all-solid-state\nbatteries. It reports the discovery of a Li-Al-Zr-Cl-O composition that exhibits not only high ionic\nconductivity with relatively low raw material costs but also an exceptionally low hardness of 0.22 GPa.\nThis hardness is significantly lower than that of other solid electrolytes previously considered\ncompliant materials. While individual properties of the Li-Al-Cl-O and Li-Zr-Cl-O material classes\nhave been reported previously and are not entirely novel, this manuscript provides helpful clarification\nby demonstrating that these desirable characteristics can be simultaneously achieved by combining\nthese two material classes.\nAlthough this finding is valuable, the materials characterization presented in the manuscript is\nrelatively weak, despite the work focusing on the identification of a specific composition within an\nalready known material system. In this regard, I believe the manuscript has the potential to be\npublished in Nature Communications after addressing the following major concerns.\n(1) Clarification on Mixed-Anion Materials and Mechanical Properties (Page 6):\nThe authors state that “materials with two types of anions are usually much more compliant than those\nwith only one.” This statement is misleading, as \"softness\" is not a general characteristic of mixed-\nanion materials. Mechanical properties are primarily determined by bonding nature within specific\ncrystal structures or local atomic arrangements, not simply by the presence of multiple anions. The\nauthors should clarify the specific mechanisms or structural features by which anion mixing leads to\nenhanced compliance in this system.\n(Response) We sincerely thank the reviewer for his/her careful assessment of our manuscript and the\ninsightful, constructive suggestions. The direct cause of the mechanical compliance is indeed the\natomic configuration and the associated bonding nature, instead of the coexistence of multiple anions\nitself. The mechanism that the materials with mixed anions are frequently more compliant is now\nindicated on page 6: “First of all, compared with the materials with only one type of anion, those with\ntwo types of anions have often been found to display the kind of atomic configuration that enables\nhigher mechanical compliance25,39,40. In such materials, the coexisting anions frequently make the\ncation-anion polyhedra more distorted and disordered, so that the backbone of the atomic framework\nbecomes more easily rotated or bended, leading to enhanced mechanical compliance25,39,40; this\nphenomenon has been observed in multiple solid electrolytes, including the O-modified Na PS 40,\n3 4\n2 6 4\n(2) Misleading Analysis of Amorphous and Crystalline Phases:\ni) XRD Interpretation (Figure 1d, 1e, and Supplementary Figures):\nThe small peaks observed in the XRD patterns are attributed to either P3m1 or C2/m space groups.\nThe manuscript presents this as though portions of LZACO crystallize in these specific phases.\nHowever, these peaks correspond to characteristic reflections of fcc or hcp anion packing (e.g., LiCl\ntypically exhibits fcc anion packing). The C2/m and P3m1 structures in this material class are part of\nthese broader anion packing frameworks. It is therefore an overstatement to attribute these peaks\ndefinitively to C2/m or P3m1 space groups without further evidence.\n(Response) We fully agree with the reviewer that these peaks should not be attributed definitively to\nthe C2/m or the  3  1 structures, and we thank the reviewer for helping us clarify this important\npoint. In the revised manuscript, the structures originally assigned as the C2/m and the  3  1 space\ngroups are only described as the structures showing the cubic close-packed (ccp) and the hexagonal\nclose-packed (hcp) anion configurations, respectively. The revision is made on page 10: “Although the\nlow crystallinity of xLi O-(1-y)ZrCl -yAlCl prevents the precise crystal structure determination, the\n2 4 3\nXRD patterns may still disclose certain information regarding the atomic configuration. Generally\nspeaking, the characteristic reflections of up to two types of crystal structures can be identified; both\nhad been frequently observed in the Li MCl -type chloride solid electrolytes48. One of them is the\n3 6\nstructure showing the hexagonal close-packed (hcp) anion arrangement; the materials displaying this\nkind of structure include the Li ZrCl with the  3  1 space group47,49 and the Li YCl with the Pnma\n2 6 3 6\nspace group48. The other is the structure showing the cubic close-packed (ccp) anion arrangement; the\nmaterials displaying this type of structure include the LiCl with the   3   space group48 and the\nLi ScCl with the C2/m space group50. Due to the low crystallinity of LZACO, it is difficult to\n3 6\nconclusively determine which specific structures mentioned above is displayed by each phase.\nConsequently, the two crystalline phases present in LZACO would be generally referred to as the hcp\nand ccp phases, respectively, in the discussion below.”.\nii) Precipitation vs. Allotropes in XRD Observations:\nThe XRD peaks observed are more likely due to the precipitation of Li-(Al, Zr)-Cl phases rather than\ncrystalline forms of the oxychloride. This suggests segregation of stable phases from a metastable\namorphous matrix. However, the authors suggest that the oxychloride phase itself consists of\ncrystalline and amorphous regions, which is not convincingly supported by the data. If the authors\ncontend that these crystalline phases are allotropes of the oxychloride, additional supporting\nevidence should be provided.\n(Response) We thank the reviewer for pointing out this important issue. It is indeed possible that the\ncrystalline phases are precipitates showing different compositions from the amorphous matrix.\nPrecisely determining the composition of the extremely small crystallites in LZACO (about 15 nm)\nrequires elemental mapping at very high magnifications using transmission electron microscopy, but\nthe intense electron beam needed for such characterization would damage the electron-beam sensitive\noxychloride solid electrolytes, preventing the conclusive composition determination. In light of this\nfact, we cease to definitively describe the crystalline phases as the allotropes of LZACO, but emphasize\n2\nthe possibility that the crystalline and amorphous phases in this material might be compositionally\ndifferent. The revision is made on page 9: “It must be emphasized that the compositions of such minor\ncrystalline species are not necessarily identical with that of the amorphous matrix. Instead, it might be\nthe Li-M-Cl (M = Zr and/or Al) precipitates, which are much more difficult to amorphize than the\noxychlorides25,42. The precise composition determination for the minor crystalline phases here would\nrequire the elemental mapping at magnifications no lower than those in the HRTEM image presented\nabove (Supplementary Fig. 5a), but the intense electron beam needed for such characterization would\nrapidly damage the electron-beam sensitive oxychloride solid electrolytes. Consequently, the\ncomposition of the crystalline phase cannot be conclusively determined. Fortunately, their volume\nfraction (about 10% as mentioned above) is too low to considerably influence the overall ion\ntransport.”.\niii) PDF Analysis (Supplementary Figure 4):\nThe pair distribution functon(PDF) analysis shows distinct peaks extending to long radial distances,\nwhich is characteristic of crystalline rather than amorphous materials. While radial distribution\nfuncton(RDF) peaks can sometimes result from artifacts in the Fourier transform process, the current\ninterpretation of the PDF data is misleading. The authors should revise their interpretation or\nreanalyze the data to avoid misinforming readers.\n(Response) We thank the reviewer for prompting us to consider this important issue. It should be noted\nthat the PDF data presented in Supplementary Fig. 4 only describes the atomic configuration up to r\nof 30 Å, i.e., 3 nm, while the crystallites scattered in the amorphous matrix could in fact be as large as\naround 15 nm, according to the HRTEM image in Supplementary Fig. 5d. Consequently, at the r  3\nnm range for the PDF, the weak crystalline characteristics are supposed to be present, and such a feature\ndoes not conflict with the low crystallinity indicated by HRTEM. This point is emphasized on page 9:\n“Such a crystallite size (around 15 nm) explains why the PDF of the highly amorphous LZACO\nmaterial (Supplementary Fig. 4) still shows weak peaks characterizing ordered crystalline structures\nup to r = 30 Å (3 nm).”.\niv) TEM/FFT Analysis (Supplementary Figure 5):\nThe interpretation of the TEM and FFT patterns in Supplementary Figure 5 appears inconsistent.\nIf the two spots observed in the FFT pattern (Figure 5b) represent a crystalline feature, they suggest\na single crystal orientation. However, the regions claimed to be crystalline in the TEM image in Figure\n5d are scattered , which should result in a ring-like FFT pattern, not discrete spots. This inconsistency\nneeds to be addressed, as it undermines the interpretation of the sample’s microstructure.\n(Response) We thank the reviewer for raising this important point. Supplementary Fig. 5d in the\noriginal submission is the inverse FFT pattern generated from the two spots of the FFT pattern in\nSupplementary Fig. 5b, so what can possibly appear in Supplementary Fig. 5d are only the crystallites\ngiving rise to these two particular spots in the FFT pattern. However, among the crystalline regions\ndisclosed this way, only the relatively large region at the left side of Supplementary Fig. 5d is truly\ncrystalline, while the other extremely small “crystalline” regions are the artifacts associated with the\ninverse FFT processing, rather than real crystallites. This can be proved by conducting FFT analysis\non different regions of the original HRTEM image: except the aforementioned region at the left side\n3\nof the image, none of the other regions can give rise to visible spots in the FFT pattern (examples are\npresented as Supplementary Fig. 5e and f, which are also pasted below). That is, the only true\ncrystalline region in Supplementary Fig. 5d is the relatively large one at the left side; there is indeed\nonly one crystalline region here, rather than multiple scattered, extremely small ones, as pointed out\nby the reviewer. This is clarified on page 9: “The size and morphology of the crystalline regions can\nbe probed by conducting inverse FFT using these two weak spots. As shown in Supplementary Fig. 5d,\nsuch processing discloses one relatively large crystalline region at the left side of the image and several\nscattered, extremely small ones. Unlike the former, the latter should be the artifacts resulting from the\ninverse FFT processing, rather than true crystallites; when FFT was conducted locally at different\nregions in Supplementary Fig. 5c, the aforementioned relatively large crystalline region is in fact the\nonly one that can give rise to spots in the FFT pattern (Supplementary Fig. 5e), and the same happens\nto none of the other regions (example shown in Supplementary Fig. 5f).”.\nSupplementary Fig. 5. a HRTEM image of LZACO. b FFT pattern of the area delineated by the red dashed\nrectangle in (a). The spots arising from the crystalline phase are highlighted by the red circles. c HRTEM image\nof the area delineated by the red dashed rectangle in (a). d Inverse FFT pattern using the spots circled in red in\n4\n(b). Region I in (c) are the same area as Region I in (d), while the same applies to Region II as well. e, f FFT\npatterns of Region I (e) and Region II (f) in (c), respectively, with the spots arising from the crystalline phase\nhighlighted by the red circles.\n(3) Nanoindentation Data Interpretation (Figure 2a):\nFigure 2a presents the Young’s modulus and hardness of various materials measured by\nnanoindentation on cold-pressed pellets using a Berkovich tip. While nanoindentation is a well-\nestablished method, accurate measurements require samples with surfaces flat relative to the tip radius\nand near-full densification (≈100% density). Cold-pressed pellets often do not meet these criteria.\nTherefore, the manuscript should include surface micrographs and representative load-displacement\n(or stress-strain) curves for each measurement, rather than reporting only final values. This additional\ndata would substantiate the reliability of the mechanical measurements.\n(Response) We sincerely thank the reviewer for this valuable suggestion. As mentioned in the main\ntext, among the solid electrolytes with definitive values for both the hardness and Young’s modulus in\nFig. 2a, only LZACO was characterized through our own nanoindentation measurement; most data in\nthis figure are in fact the reported values in literature. Thanks to the excellent mechanical compliance\nof LZACO, its cold-pressed pellet may indeed reach a relative density of 96.13%, rather close to 100%.\nTherefore, the data should be reliable. In the revised manuscript, the SEM image of the cold-pressed\nLZACO pellet and the representative load-displacement curves are both presented. These contents are\npresented on page 15: “To ensure the reliability of these mechanical characterization results, we\nconducted scanning electron microscopy (SEM) observation on the surface of the cold-pressed\nLZACO pellet fabricated under 300 MPa (the same as that used for the characterizations above in Fig.\n2a). It is found that such a pellet is almost fully densified (Supplementary Fig. 9). In particular, most\nof the black spots that look like pores are in fact also solid substances too, as shown in the image at\nhigher magnification (Supplementary Fig. 9b); they could be the minor crystalline precipitates that are\ncompositionally different from the amorphous matrix. Using the Adjust-Threshold plugin of ImageJ51,\nthe relative density of the pellet is measured to be 96.13%. Such an almost fully densified pellet ensures\nthe flat, nearly pore-less surface needed for reliable nanoindentation measurements; several\nrepresentative nanoindentation load-displacement curves acquired from this cold-pressed LZACO\npellet are also presented in Supplementary Fig. 10.”.\nSupplementary Fig. 9. SEM images of the cold-pressed LZACO pellet fabricated under 300 MPa (the same as\nthat for the cold-pressed pellet used in the nanoindentation experiments).\n5\n50 50 50\n40 40 40\n30 30 30\n20 20 20\n10 10 10\n0 0 0\n0 600 1200 1800 2400 3000 0 600 1200 1800 2400 3000 0 600 1200 1800 2400 3000\nSupplementary Fig. 10. Representative nanoindentation load-displacement curves for the cold-pressed\nLZACO pellet fabricated under 300 MPa.\n(4) Comparison with Li-Al-Cl-O Reference Data:\nPrevious studies have already demonstrated that Li-Al-Cl-O materials are exceptionally compliant\ncompared to other chloride-based solid electrolytes. Thus, it is important for the authors to\ncontextualize the mechanical properties of LZACO by comparing them directly with both Li-Zr-Cl-O\nand Li-Al-Cl-O. While data for Li-Zr-Cl-O is included in Figure 2a, comparable data for Li-Al-Cl-O—\narguably a more relevant benchmark—is missing. The authors should provide nanoindentation results\nfor Li-Al-Cl-O in Figure 2a for a more comprehensive comparison.\n(Response) We thank the reviewer for raising this important point. The Li-Al-Cl-O solid electrolytes\ncan indeed achieve exceptional mechanical compliance; when displaying the optimal mechanical\nproperties, this type of materials even ceases to take the powdery form, but become a viscoelastic\nsubstance resembling polymer, whose mechanical compliance will surpass the powdery solid\nelectrolytes like LZACO for sure. However, such viscoelastic solid electrolytes cannot be easily\nfabricated into pouch-cell films using the cost-effective dry-film technology, as it would easily\noverflow under the pressure during rolling and could also stick to the rollers. In this regard, the LZACO\nmaterial that remains powdery but displays a relatively high mechanical compliance appears more\ndesirable.\nAlthough the viscoelastic Li-Al-Cl-O is certainly more compliant than the powdery LZACO as\nmentioned above, the quantitative comparison requested by the reviewer is challenging: the extremely\nlow hardness of these materials makes it difficult to conduct the nanoindentation measurements.\nRegardless, we still qualitatively emphasize this fact on page 16: “Here, it must be emphasized that,\nas a powdery solid electrolyte, the mechanical compliance of LZACO cannot possibly surpass the\nviscoelastic ones, such as the polymer solid electrolytes and the recently reported Li-Al-Cl-O solid\nelectrolytes with unique pliability39,41,42. Instead, the advantage of LZACO in mechanical compliance\nexists only among the powdery solid electrolytes, which occupy the vast majority of the inorganic solid\nelectrolytes studied so far and appear more compatible with the dry-film technology for pouch-cell\nfabrication52,53.”.\n(5) Battery Performance and SEM Analysis (Figures 2c and 2e):\nThe cycling performance of the battery incorporating LZCO (Figure 2c) appears significantly poorer\nthan comparable data for chloride or oxychloride electrolytes in the literature. This could mislead\n6\n)Nm(\necroF\na\nPenetration depth (nm)\n)Nm(\necroF\nb\nPenetration depth (nm)\n)Nm(\necroF\nc\nPenetration depth (nm)\nreaders regarding the material’s true potential.\n(Response) We thank the reviewer for these valuable and insightful questions. Here we would like to\nemphasize that the cell configuration and cycling conditions for the LZCO-based cell in Fig. 2c are\nmuch harsher than those usually applied in literature: the cathode active material mass loading reaches\n27 mg cm2, instead of the 56 mg cm2 typically employed in previous studies, and the cell is also\ncycled at a relatively low rate of 0.1 C, so that the volume change of both the cathode active material\nparticles and the entire composite cathode layer would be much larger than that in the typical LZCO-\nbased cells in literature. Under this circumstance, only the highly compliant solid electrolyte can enable\ndecent cycling performance. With the limited compliance observed for LZCO (as shown in Fig. 2a),\nwe indeed found this material not capable of enabling satisfactory cycling stability at such conditions.\nMoreover, the SEM image in Figure 2e reveals an excessive volume of voids. If these voids result from\nthe volume change of cathode materials, then the entire cathode layer thickness should expand\nproportionally, which is not evident.\n(Response) Regarding the thickness of the entire composite cathode layer, we would like to clarify that\nthe heights of the lamellas in Fig. 2e and f are in fact not the thicknesses of the composite cathode\nlayers. Since the cathode active material mass loading of the composite cathodes studied here is around\n25 mg cm2, the thickness of the composite cathode layer should at least be tens of micrometers; in\ncontrast, the “lift-out” method for focused-ion beam (FIB) sample preparation may only cut a much\nsmaller depth (about 10 m) into the surface of the pellet. Therefore, no matter how thick the composite\ncathode layer is, the lamella samples prepared by FIB would always be about 10 m high, as shown\nFig. 2e and f, and such heights by no means reflect the thicknesses of the composite cathode layers.\nWe apologize for not making this point clear enough in the original submission. It is now emphasized\non page 18: “It should be noted that FIB may cut only about 10 m deep into the surface of the pellet,\nwhich is much smaller than the thicknesses of the composite cathode layers with the high CAM mass\nloading of around 25 mg cm2 here (at least tens of micrometers). Therefore, the height of the lamella\nprepared this way can by no means reflect the thickness of the corresponding composite cathode layer.”.\nIt is more likely that these voids were present prior to battery assembly, suggesting poor electrode\nfabrication. This fabrication issue could account for the poor electrochemical performance shown in\nFigure 2c. The authors should clarify this point and, if applicable, improve their cell assembly to better\nrepresent the intrinsic properties of the electrolyte.\n(Response) We thank the reviewer for pointing out this important issue. However, we believe the voids\nshould still form after cycling, because otherwise the LZCO-based cell in Fig. 2c cannot possibly reach\nan initial discharge capacity almost identical with that of the LZACO-based cell in Fig. 2d (176.1 and\n178.9 mAh g1, respectively). To demonstrate this point, we conducted another FIB-SEM observation\nto the composite cathode of the LZCO-based cell before cycling. It was found that the volume of voids\nis no larger than that of the composite cathode of the LZACO-based cell after 10 cycles, which shows\na discharge capacity nearly the same as the initial value (177.7 vs. 178.9 mAh g1) and thus is not\nsupposed to undergo any non-negligible interfacial contact loss yet. These contents are presented on\npage 18: “Here, it needs to be emphasized that the large voids observed in Fig. 2e must mostly emerge\n7\nafter cycling, instead of pre-existing in as-assembled cells, because otherwise the Li-In | LPSCl-LZCO\n| scNCM92 cell in Fig. 2c cannot possibly deliver an initial discharge capacity similar to that of the Li-\nIn | LPSCl-LZACO | scNCM92 cell in Fig. 2d (176.1 and 178.9 mAh g1, respectively). In fact, the\nvolume of voids in the composite cathode of the as-assembled Li-In | LPSCl-LZCO | scNCM92 cell is\nindeed limited; it is comparable to the volume of voids in the Li-In | LPSCl-LZACO | scNCM92 cell\nafter 10 cycles (Supplementary Fig. 11), where no considerable interfacial contact loss is supposed to\noccur, as indicated by the discharge capacity nearly identical to the initial value (177.7 and 178.9 mAh\ng1, respectively).”.\nSupplementary Fig. 11. a SEM image of the composite cathode of the Li-In | LPSCl-LZCO | scNCM92\ncell prior to cycling. b SEM image of the composite cathode of the Li-In | LPSCl-LZACO | scNCM92\ncell after 10 cycles under the conditions shown in Fig. 2d.\nSummary\nThe manuscript presents an important advancement in the design of compliant solid electrolytes for\nall-solid-state batteries. However, substantial revisions are required to strengthen the materials\ncharacterization, clarify data interpretation, and ensure the reliability of the reported findings.\nAddressing the points above will significantly enhance the manuscript’s clarity, rigor, and impact,\nmaking it suitable for publication in Nature Communications.\n(Response) Once again, we sincerely thank the reviewer for his/her positive comments on our work\nand the insightful, valuable suggestions that greatly helped in strengthening the present study.\nHopefully the revision presented here can properly address the reviewer’s concerns.\nI believe this manuscript will make a significant contribution to the solid state battery field, presenting\na low cost solid state electrolyte for dry and wet process of fabrication cells with high nickel content.\nThe authors' approach integrates this research from lab scale to large scale application – pouch cell.\nTo enhance clarity and support the authors' claims, the following points should be considered:\n(1). Please consider about the title associated with the work, because the work is related to the low\ncost of materials and solid state battery, examples below. I believe that you have opinions and\nunderstanding which title is better for your work.\n- Cost-Effective and Mechanically Compliant LZACO: Advancing All-Solid-State Li Batteries,\n- Enhancing All-Solid-State Li Battery Performance with LZACO: A New Standard in Electrolytes,\n- LZACO Solid Electrolyte: Achieving High Performance and Commercial Viability in Li Batteries.\n(Response) We deeply appreciate the reviewer’s positive feedback and insightful suggestions. To\nfurther emphasize the advantage of the material reported here, we changed the title to “Mechanically\ncompliant and cost-effective 1.4Li O-0.75ZrCl -0.25AlCl solid electrolyte for all-solid-state batteries\n2 4 3\nwith superior cycling stability”.\n(2) How does the mechanical compliance of LZACO compare to other solid electrolytes in practical\napplications?\n(Response) We thank the reviewer for raising this important point. The mechanical compliance of\nLZACO, as reflected by its hardness and Young’s modulus, greatly exceeds those of other widely\nstudied solid electrolytes, which has been illustrated in Fig. 2a. In practical applications, this advantage\nis reflected in the cell performance at low stacking pressures; since the high stacking pressures above\nstate cell at the practically viable but much lower stacking pressures would have to to rely on the high\nmechanical compliance of the solid electrolyte to maintain the intimate solid-solid contact and thereby\nthe decent cycling stability. To probe this characteristic for LZACO, we tried to compare the\nperformance of the all-solid-state cells formed by LZACO and those formed by two other prototypic\nZr-based (oxy)chloride solid electrolytes, Li ZrCl (LZC) and Li ZrCl O (LZCO), under a low\n2 6 1.75 4.75 0.5\nstacking pressure of 5 MPa. Additionally, the performance of such LZACO-based cells was also\ncompared with other cells under low stacking pressures in literature. These comparisons all suggest\nthat the mechanically compliant LZACO is advantageous in enabling low-pressure cell performance,\nso it should favor practical applications. The detailed comparison and discussion are presented on page\n36: “For comparison, we also tried to replace the LZACO in the cells above with Li ZrCl (LZC) or\n2 6\nLZCO (both are much less compliant than LZACO, as shown in Fig. 2a), and then conducted the\ncycling tests under the same conditions, especially the low stacking pressure of 5 MPa. The variation\ntendency of the cell performance was found consistent with that of the mechanical compliance\ndisclosed in Fig. 2a. As shown in Supplementary Fig. 19, the least compliant LZC solid electrolyte\nresults in the poorest cycling performance; the capacity retention after 100 cycles is only 51.09%.\nIn comparison, the relatively more compliant LZCO enables better cycling stability, with the capacity\nretention being 69.21% after 100 cycles. As for LZACO, its mechanical compliance greatly exceeds\n9\nthose of both LZC and LZCO (Fig. 2a), so this material enables the most stable cycling performance;\nafter 100 cycles, the capacity retention is 91.52%. In addition to the two typical Zr-based (oxy)chloride\nsolid electrolytes for comparison above, the mechanically compliant LZACO can also enable better\ncell performance than many other widely studied solid electrolytes. As shown in Supplementary Table\n8, the cycling performance achieved by the LZACO-based cells at 5 MPa even surpasses that of certain\ncells at higher pressures such as 10 MPa11,35,78. These observations demonstrate the advantage of the\nmechanically compliant LZACO in enabling decent cell performance at low stacking pressures, which\nis a prerequisite for constructing practical ASSLBs.”.\n240\n180\n120\n60\n0 20 40 60 80 100\nSupplementary Fig. 19. a−c Long-term cycling performance of the Li Si | LPSCl-LZC | scNCM92\n13 4\ncell (a), Li Si | LPSCl-LZCO | scNCM92 cell (b), and Li Si | LPSCl-LZACO | scNCM92 cell (c)\n13 4 13 4\nunder 5 MPa at 30 C.\n10\n)1-g\nhAm(\nyticapaC\nc\n100\n91.52% capacity retention 90\n(100 cycles)\nDischarge 30 C, 66 mA g-1 (0.33 C), 5.29 mg cm-2\n2.0 ¾ 4.3 V vs. Li/Li+\n)%(\nycneiciffe\ncibmoluoC\n180\n135\n90\n45\n0\n0 20 40 60 80 100\n200\n150\n100\n50\n0\n0 20 40 60 80 100\nCoulombic efficiency\n)1-g\nhAm(\nyticapaC\nb\n100\n90\n69.21% capacity retention 80\n(100 cycles)\n2.0 ¾ 4.3 V vs. Li/Li+\n)%(\nycneiciffe\ncibmoluoC\nCoulombic efficiency\n)1-g\nhAm(\nyticapaC\na\n100\n90\n80\n51.09% capacity retention\n(100 cycles) 70\nCharge Li13Si4 | LPSCl-LZC | scNCM92 60\nDischarge 30 C, 66 mA g-1 (0.33 C), 5.17 mg cm-2\n2.0 ¾ 4.3 V vs. Li/Li+\n)%(\nycneiciffe\ncibmoluoC\nCoulombic efficiency\nSupplementary Table 8. Low-pressure cycling performance of the LZACO-based ASSLBs and those\nbased on other solid electrolytes.\nSpecific\nStacking\nTemperature\nCAM Catholyte current Capacity retention Ref.\npressure\n(C)\n(mA g−1)\n(MPa)\n95% (69 cycles)\nLiNi0.92Co0.06Mn0.02O2 LZACO 30 5 90% (119 cycles)\n(0.33 C) work\n80% (215 cycles)\n~70\nLiCoO2 Li1.625Al0.375Zr0.625Cl5.25 30 9.62 ~58.71% (282 cycles) (78)\n(0.5 C)\n~70\nLiCoO2 Li2ZrCl6 30 9.62 ~48.74% (109 cycles) (78)\n(0.5 C)\n2 65% (50 cycles) (35)\nLiNi0.83Co0.11Mn0.06O2 Li3InCl6 n/a 80\n10 93% (50 cycles) (35)\n~66\nLiNi0.5Co0.2Mn0.3O2 Li0.388Ta0.238La0.475Cl3 30 ~2 81.6% (100 cycles) (11)\n(0.44 C)\nWhat specific tests or methods were used to measure the hardness and Young’s modulus of LZACO?\n(Response) The hardness and Young’s modulus were measured by SEM-based nanoindentation and\natomic-force spectroscopy, respectively. The details of measurements are described on page 43: “The\nhardness of the solid electrolyte was measured by conducting nanoindentation within SEM using the\nHysitron PI 88 in situ nanoindenter with a Berkovich tip under a high load regime. The samples were\ntransferred into the SEM by an air-tight transfer holder to avoid air exposure. The hardness was\ncalculated from the unloading curve using the method developed by Oliver and Pharr85,86. The Young’s\nmodulus of the solid electrolyte was measured by atomic force microscopy (AFM) in peak force\nquantitative nanomechanical mapping mode and analyzed by Derjaguin-Muller-Toporov model. The\nAFM tip (RTESPA-300) is made of Sb-doped Si; it shows the rectangular geometry, a radius of 8nm,\nand a spring constant of 40 N m1. The AFM instrument was placed in an Ar-filled glovebox with H O\n2\nand O contents both below 0.01 ppm.”.\n2\n(3). The cost-effectiveness of LZACO with a raw materials cost of $10.61/kg. How was this cost\ncalculated, and what factors contribute to its competitiveness? Are there any potential fluctuations in\nraw material prices that could affect the cost-effectiveness of LZACO?\n(Response) We thank the reviewer for these thoughtful inquiries. To begin with, we would like to first\nclarify that our discussion in the revised manuscript is no longer based on the cost per unit mass of the\nsolid electrolyte, but on the cost per unit volume of the solid electrolyte; since the optimal volume of\n11\nthe solid electrolyte in all-solid-state cells (consisting of the solid-electrolyte volume to realize optimal\ntortuosity in the composite cathode and that to realize the desirable thickness for the individual solid-\nelectrolyte layer) does not vary with the type of the solid electrolyte, the cost per unit volume of the\nsolid electrolyte can more straightforwardly reflect the contribution of the solid-electrolyte cost to the\noverall cell production cost. The method for calculating this cost is described on page 44: “The cost\nper unit volume of the solid electrolyte for discussion here is calculated by multiplying the cost per\nunit mass of the solid electrolyte and the density of the solid elecrolyte. While the method of density\nmeasurement has already been described in the “Structure and morphology characterizations” section\nabove, the cost per unit mass of the solid electrolyte was calculated straightforwardly from the average\nmarket prices of the corresponding raw materials as the industrial commmodity chemicals in the year\nof 2024. These prices and the information sources are listed in Supplementary Table 1.”.\nSupplementary Table 1. Average market prices of the industrial commodity chemicals in 2024 and\nthe sources from which these prices are acquired.\nAverage market price in 2024\nCommodity chemical Sources\n($ kg1)\nLi2O 210.67 LB Group Co., Ltd.\nShandong Hongyang Chemical\nLiCl 14.04 Co., Ltd.\nChengxin Lithium Group Co.,\nLi2CO3 12.64\nLtd.\nCBC Metal\nZrCl4 11.24\n(https://www.cbcie.com/)\nAsian Metal\n(https://www.asianmetal.cn/)\nAlCl3 0.84\nShanghai Metals Market\n(https://www.smm.cn/)\nAs for the factors contributing to the cost-competitiveness of LZACO and the influence of potential\nprice fluctuations, these two issues may be discussed together. The major reason that LZACO shows\ndesirable cost-effectiveness lies in the fact that it can be synthesized by using highly affordable\nchemicals only, i.e., Li CO , ZrCl , and AlCl . If the prices of these chemicals fluctuate significantly,\n2 3 4 3\nthe cost of the solid electrolyte will inevitably be influenced, as noted by the reviewer. Fortunately,\nthese chemical prices are relatively stable in the past two years. Regardless, we still tried to avoid the\npotential distraction from chemical price fluctuation by utilizing the average market price in 2024 for\nestimation in the revised manuscript. The results of such cost analysis are presented on page 23: “These\ndata suggest that high-quality LZACO can be synthesized from the cost-effective Li CO , ZrCl , and\n2 3 4\nAlCl , whose average market prices in 2024 as the industrial commodity chemicals are $12.64 kg1,\n3\n$11.24 kg1, and $0.84 kg1, respectively (Fig. 3d and Supplementary Table 1). Based on these\nchemical prices and the density of LZACO (measured to be 2.15 g cm3; detailed procedure described\n12\nin Methods), the raw materials cost of this solid electrolyte can be estimated as $22.77 L1 (Fig. 3e).\nIn comparison, if the much more expensive Li O ($210.67 kg1), instead of the Li CO with $12.64\n2 2 3\nkg1 cost, is used to synthesize LZACO, the raw materials cost would be $92.94 L1, which is over\nfour times that of the Li CO -synthesized LZACO ($22.77 L1, as mentioned above) and also greatly\n2 3\nexceeds the $46.75 L1 solid-electrolyte raw materials cost for enabling reasonable ASSLB cost.\nTherefore, the fact that LZACO may be synthesized directly from the affordable Li CO is crucial to\n2 3\nthe cost-effectiveness of this solid electrolyte. In addition, since the synthesis of LZACO involves the\nrather cost-effective AlCl ($0.84 kg1) but does not rely on the relatively expensive LiCl ($14.04 kg1),\n3\nits raw materials cost is also lower than those of other previously reported Zr-based (oxy)chloride solid\nelectrolytes (Fig. 3e).”.\n600\n400\n200\n0\n270 290 310 330 10 20 30 40 50 60 70 80 0 200 400 600\nFig. 3 | Cost-effectiveness of LZACO. a Electron energy-loss spectra of the LZACO synthesized\nusing Li CO , ZrCl , and AlCl as the raw materials. For comparison, the C-K spectrum of CaCO is\n2 3 4 3 3\nalso displayed. b XRD pattern of the LZACO synthesized using Li CO , ZrCl , and AlCl as the raw\n2 3 4 3\nmaterials. c Nyquist plot of the LZACO synthesized using Li CO , ZrCl , and AlCl as the raw\n2 3 4 3\nmaterials. The measurement was conducted at 25 C. d Average market prices in 2024 for the industrial\ncommodity chemicals involved in the cost estimation. e Raw materials costs of LZACO and two other\nrepresentative Zr-based (oxy)chloride solid electrolytes, Li ZrCl and Li ZrCl O .\n2 6 1.75 4.75 0.5\n(4). What is the environmental impact of producing and using LZACO, considering both the raw\nmaterials and the manufacturing process?\n(Response) We thank the reviewer for raising this important point. The environmental impact is\ndiscussed on page 25: “For a 100-m3 dry room, the power needed to maintain the 1% relative humidity\nis about 1.5 times that for the 3.85% relative humidity, and the difference will become larger for larger\ndry rooms. Consequently, the superior humidity tolerance of LZACO (stable up to around 4% relative\n13\n)mc\nW(\n''Z-\nc\ns25 C = 2.59 mS cm1\nZ' (W cm)\n215\n210\n205\n10\n5\n0\n)1-gk\n$(\necirp\ntekram\negareva\n4202\n60\n$210.67 kg-1\n40\n$14.04 kg-1 $12.64 kg-1\n$11.24 kg-1\n20\n$0.84 kg-1\n)1-L\n$(\ntsoc\nslairetam\nwaR\n$46.75 L-1\n$30.68 L-1\n$24.70 L-1\n$22.77 L-1\nLiCl Li2CO3 ZrCl4 AlCl3 Li2ZrCl6 Li1.75ZrCl4.75O0.5 LZACO\n).u.a(\nytisnetnI\nb\nLZACO synthesized using Li2CO3\nC2/m Li3ScCl6 (ccp)\nP3m1 Li2ZrCl6 (hcp)\n2q (degree)\n).u.a(\nytisnetnI\na\nLZACO synthesized using Li2CO3\nCaCO3\nC-K\nEnergy Loss (eV)\nd e\nhumidity at 25 C as mentioned above) can greatly save the power needed for handling and storage,\nwhich makes its large-scale production cost-effective and also environmentally friendly. Besides, even\nif LZACO or any of its raw materials is accidentally exposed to the atmosphere with overly high\nhumidity, it will not release the toxic and flammable H S gas like the sulfide solid electrolytes61, but\n2\nis only supposed to generate the much less hazardous HCl like other chloride solid electrolytes61,62.\nThe cost-effectiveness and eco-friendliness of LZACO make it suitable for large-scale commercial\nutilization.”.\n(5) What future research directions or improvements are suggested by the authors to further enhance\nthe performance and applicability of LZACO? Are there any potential barriers to further development\nand commercialization that need to be addressed?\n(Response) We thank the reviewer for these thoughtful and insightful inquiries. The future directions\nfor improvement and the potential barriers are discussed on page 37: “Furthermore, it should also be\nnoted that the low-pressure cell performance achieved here still has very large room for improvement,\nbecause, due to the poor reduction stability of LZACO (reduction potential 1.62 V vs. Li/Li+, as shown\nin Supplementary Fig. 14), the anolyte of the cell above is still the commonly used LPSCl, which is\nmuch less compliant than LZACO (as shown in Fig. 2a) and thus unlikely to perform well at low\nstacking pressures. If an anode-compatible solid electrolyte that is as compliant as LZACO can be\ndeveloped in the future, the low-pressure cell performance similar to those at high stacking pressures\nshould be achievable. To this end, the interphase resulting from the reduction of the solid electrolyte\nmust be electron-blocking, so that the electrons needed for further reduction cannot migrate through\nto reach the unreacted solid electrolyte79. Considering that the Zr4+ and Al3+ in LZACO would\ninevitably be reduced into electronic conductors such as Zr and Al by Li metal80,81, the presence of\nsuch metal cations should preferably be eliminated in the material. Instead, the solid electrolyte needs\nto be populated by non-metal cations such as P5+ and B3+, which will only be reduced into electron-\nblocking species79. If desirable mechanical compliance and ionic conductivity can be realized in such\nmaterials through rational materials design too, the cost-effective ASSLBs that can operate at\nsufficiently low stacking pressures for practical application may be expected.”\n(6) Phase-field modeling to compare LZACO and LZCO. How do the computational results align with\nthe experimental findings, and what insights do they provide about the mechanical compliance of\nLZACO?\n(Response) We appreciate the reviewer's attention to these important issues. As mentioned on pages\n1719, the computational results align well with the experimental findings. While the phase-field\nmodeling suggests that LZCO would be more easily detached from the cathode than LZACO, this\ncharacteristic is indeed verified by the direct SEM observation of the composite cathode of the cycled\ncells (Fig. 2e and f); besides, the LZCO-based cell also shows much poorer cycling stability than the\nLZACO-based one with the same cell configuration (Fig. 2c and d), consistent with the aforementioned\nSEM observation. These corroborating computational and experimental results suggest that LZACO\ndisplays much better mechanical compliance than LZCO.\nWhat specific experimental setups and conditions were used to validate the computational results, and\n14\nhow do these setups ensure the reliability of the findings?\n(Response) The experimental verification of the computational results was conducted by comparing\nthe LiIn | LPSCl-LZCO | scNCM92 and LiIn | LPSCl-LZACO | scNCM92 cells. Both cells employ\nrelatively low cycling rate of 0.1 C and relatively high cathode active material mass loading of around\n25 mg cm2 to maximize the volume change of the cathode active material particles and the composite\ncathode layer, respectively, so that only the highly compliant solid electrolytes may accommodate such\nlarge volume change during cycling. As mentioned on pages 1719, the LZCO-based cell under such\nconditions does display much poorer cycling stability than the cell based on the more compliant\nLZACO, consistent with the computational prediction that LZCO is less effective in sustaining the\nsolid-solid contact than LZACO. Besides, the direct SEM observation of the composite cathodes in\nthese two cells after cycling also indicates that the LiIn | LPSCl-LZCO | scNCM92 cell undergoes\nmuch more severe electrode-electrolyte detachment than the LiIn | LPSCl-LZACO | scNCM92 cell. In\na word, the computational results are supported both indirectly (by the cycling stabilities of the actual\ncells, as shown in Fig. 2c and d) and directly (by the SEM observation of the cycled composite cathodes,\nas shown in Fig. 2e and f) through experiments. Therefore, the results should be reliable.\n(7) The cycling performance of cells using LZACO and LZCO. How does the mechanical compliance\nof LZACO contribute to its superior cycling performance compared to LZCO? What are the\nimplications of the observed differences in cycling performance for the practical application of LZACO\nin all-solid-state batteries?\n(Response) We are grateful to the reviewer for underscoring the importance of these issues. They are\nnow discussed on page 19: “The superior mechanical compliance of LZACO should be the key to\nmaintaining the observed intimate interfacial contact during cycling. With the extremely low hardness\nand Young’s modulus shown in Fig. 2a, LZACO will deform more easily and significantly at given\nstresses. Consequently, even if the CAM particles contacting LZACO undergo significant volume\nchange repeatedly, the LZACO particles can still change their morphologies to keep the intimate solid-\nsolid contact, thereby ensuring the high discharge capacities and decent long-term cycling stability.\nIn practical situations, the ASSLBs tend to employ highest possible CAM mass loading to maximize the\nenergy density. Besides, as mentioned in Introduction, the discharge rates would also be relatively low\nin practice, such as 0.10.3 C, which will make the discharge capacities with respect to the mass of the\nCAM higher than those at high rates. As a result, the overall volume change of both the CAM particles\nand the composite cathode layer would become more severe, making the highly compliant solid\nelectrolyte like LZACO particularly important for ensuring the decent cycling performance.”.\n(8) The impact of volume change in the composite cathode layer on the cycling stability. How does the\nmechanical compliance of LZACO help in accommodating these volume changes, and what\nadvantages does this offer for long-term stability? How do the experimental conditions (e.g., CAM\nmass loading, cycling rate) affect the observed performance, and what considerations should be taken\ninto account for practical applications?\n(Response) We thank the reviewer for asking these insightful questions. However, since the answers\nto them happen to be covered by the response to the last question too, we choose not to repeat it here\n15\nagain to save the reviewer’s time.\n(9) Li2O can be replaced by the cheaper Li2CO3 in the synthesis of LZACO. How does this substitution\nimpact the overall cost and quality of the solid electrolyte? What methods were used to confirm the\ncomplete decomposition of Li2CO3 during the synthesis process, and how reliable are these methods?\n(Response) We thank the reviewer for these thoughtful inquiries. The overall cost of the Li O-\n2\nsynthesized LZACO and that of the Li CO -synthesized LZACO are now compared on page 24: “In\n2 3\ncomparison, if the much more expensive Li O ($210.67 kg1), instead of the Li CO with $12.64 kg1\n2 2 3\ncost, is used to synthesize LZACO, the raw materials cost would be $92.94 L1, which is over four\ntimes that of the Li CO -synthesized LZACO ($22.77 L1, as mentioned above) and also greatly\n2 3\nexceeds the $46.75 L1 solid-electrolyte raw materials cost for enabling reasonable ASSLB cost.\nTherefore, the fact that LZACO may be synthesized directly from the affordable Li CO is crucial to\n2 3\nthe cost-effectiveness of this solid electrolyte.”.\nAs for the quality of the LZACO, it is not affected by replacing Li O with Li CO in the raw materials.\n2 2 3\nIn fact, according to the EIS data in Fig. 3c, the ionic conductivity of the Li CO -synthesized LZACO\n2 3\nis even slightly higher than that of the Li O-synthesized one (2.59 vs. 2.55 mS cm1 at 25 C).\n2 3\nspectroscopy (EELS) in the scanning transmission electron microscopy (STEM) mode. As a\nmicroscopy-based spectroscopy, it can detect the composition in rather local areas of the material with\nultrahigh spatial resolution. Consequently, even the impurities whose concentration is too low to be\ndetected by macroscopic techniques such as X-ray diffraction can be identified by this STEM-EELS\napproach. Therefore, the result should be very reliable.\n(10) The structural and ionic conductivity similarities between LZACO synthesized using Li2O and\nLi2CO3. How do the XRD and EELS data support these findings, and what implications do they have\nfor the practical application of LZACO? How does the ionic conductivity of LZACO synthesized using\nLi2CO3 compare to other solid electrolytes, and what factors contribute to its high performance?\n(Response) We thank the reviewer for raising these important points. As mentioned in the main text,\nthe EELS data confirm that the Li CO -synthesized LZACO does not contain any C. Therefore, the\n2 3\nLi CO used to replace Li O in the raw materials should completely decompose into Li O and CO\n2 3 2 2 2\nduring mechanochemical synthesis, resulting in the same composition as that of the Li O-synthesized\nthe LZACO synthesized through these two different approaches are the same. As for the implication\nto the practical application, it has in fact been mentioned in the response to the last question too; with\nthe expensive Li O replaced by Li CO during synthesis, the raw materials cost of LZACO decreases\n2 2 3\nsignificantly from $92.64 L1 to $22.77 L1, which is much lower than the $46.75 L1 solid-electrolyte\nraw materials cost for enabling reasonable total cell production cost.\nThe ionic conductivity of LZACO reaches 2.55 mS cm1 at 25 C, which greatly exceeds those of the\ntypical Zr-based oxychloride solid electrolytes (12 mS cm1 at 25 C) as mentioned in the main text.\nconfiguration of LZACO should be the major cause. This is discussed in-depth on page 11: “Although\nboth LZACO and the previously reported Li-Zr-Cl-O oxychlorides rely on the amorphous phase to\nrealize fast Li-ion transport, the specific atomic configurations in their amorphous phases are not the\nsame, which leads to different ion transport efficiencies. In the Li-Zr-Cl-O oxychlorides, the averaged\nZr-O and Zr-Cl bond lengths in the distorted Zr-O/Cl polyhedra are believed to be the key to the\nsuperior ion transport efficiency, as they flatten the energy landscape for Li-ion migration to lower the\noverall migration barriers25. Such a disordered atomic arrangement also occurs in LZACO, but to a\nmore pronounced degree. To characterize this behavior, we conducted the X-ray absorption\nspectroscopy (XAS). As shown in Supplementary Fig. 7a, the Zr K-edge X-ray absorption near edge\nstructure (XANES) spectrum of LZACO does not show distinct peaks like those of ZrO and ZrCl ,\n2 4\nbut appears as a broad hump, entailing that the Zr-Cl and Zr-O bond lengths in LZACO vary in a range,\ninstead of displaying definitive values. On this basis, more interesting behaviors were observed in the\nFourier transformed extended X-ray absorption fine structure (FT-EXAFS) spectra. Unlike other Li-\nZr-Cl-O solid electrolytes25, the Zr-O and Zr-Cl signals in LZACO are not distinguishable from each\nother, but nearly merge into one broad peak (Supplementary Fig. 7b). This observation suggests that\nthe Zr-O and Zr-Cl bond lengths in LZACO distribute in a broader range than those in the Li-Zr-Cl-O\nsolid electrolytes25. Besides, the FT-EXAFS spectrum of LZACO almost shows no signals above 2.5\nÅ, entailing the absence of ordering with coherence length exceeding such a distance; in contrast, other\nLi-Zr-Cl-O solid electrolytes still display minor signals in this range25. Consistent results were\nobserved in the phase-uncorrected wavelet transformed (WT) EXAFS spectrum too. While the Zr-O\nand Zr-Cl bonding still give rise to two distinct signals, respectively, in the Li-Zr-Cl-O solid\nelectrolytes25, they merge together in LZACO (Supplementary Fig. 7c). Besides, the Zr-Zr bonding at\nabout 3 Å in the WT-EXAFS spectra of typical Li-Zr-Cl-O solid electrolytes are absent in that of\nLZACO too (Supplementary Fig. 7c), confirming the absence of the ordering with such large\ncoherence lengths. These observations consistently suggest that LZACO shows a more disordered\natomic configuration than the previously reported Li-Zr-Cl-O solid electrolytes. As mentioned above,\nsuch more disordered state should supposedly favor fast Li-ion transport in Zr-based oxychlorides25,\nwhich explains the superior ionic conductivity of LZACO with respect to those of other Li-Zr-Cl-O\nsolid electrolytes (2.55 vs. 12 mS cm1 at 25 C25).”.\n17920 17990 18060 18130 18200 1 2 3 4 5\nSupplementary Fig. 7. a,b XANES (a) and FT-EXAFS (b) spectra of LZACO at the Zr K-edge. For\ncomparison, the spectra of ZrCl and ZrO are also presented. c WT-EXAFS contour plot of LZACO\n4 2\nat the Zr K-edge.\n17\n).u.a(\nnoitprosroba\ndezilaomroN\nLZACO\nZrO2\nPhoton energy (eV)\n)stinu\n.bra(\n|2k*)k(c\nTF|\nb c\n4\n3\n0\n0 5 10 15\nR (Å) k (Å-1)\n)Å(\nR\n+ R\na\nLZACO\nLZACO\nZrCl4\nZrO2 Zr-O/Cl\nZrCl4\n(11) The potential competitiveness of LZACO in terms of production cost due to its stability in humid\nair. How does this stability compare to other solid electrolytes, and what advantages does it offer for\nlarge-scale production? What specific measures or conditions are required to maintain the stability of\nLZACO during handling and storage, and how do these measures impact the overall production cost?\n(Response) We appreciate the reviewer’s insightful questions. These issues are discussed in detail on\npage 24: “When the LZACO powder was exposed to a dry room with the relative humidity of 3.85%\n(dew point set as 20 C) at 25 C for 12 h, the XRD pattern and ionic conductivity do not undergo\nconsiderable change either (Supplementary Fig. 13). In contrast, most sulfide and chloride solid\nelectrolytes cannot survive the atmosphere with relative humidity above 1%2,48; after 12-h exposure to\nsuch atmosphere, the ionic conductivities of these materials will generally decrease by at least one\norder of magnitude. For a 100-m3 dry room, the power needed to maintain the 1% relative humidity is\nabout 1.5 times that for the 3.85% relative humidity, and the difference will become larger for larger\ndry rooms. Consequently, the superior humidity tolerance of LZACO (stable up to around 4% relative\nhumidity at 25 C as mentioned above) can greatly save the power needed for handling and storage,\nwhich makes its large-scale production cost-effective and also environmentally friendly. Besides, even\nif LZACO or any of its raw materials is accidentally exposed to the atmosphere with overly high\nhumidity, it will not release the toxic and flammable H S gas like the sulfide solid electrolytes61, but\n2\nis only supposed to generate the much less hazardous HCl like other chloride solid electrolytes61,62.\nThe cost-effectiveness and eco-friendliness of LZACO make it suitable for large-scale commercial\nutilization.”.\n(12) The reduction and oxidation potentials of LZACO. How do these potentials compare to other solid\nelectrolytes, and what implications do they have for the stability and performance of LZACO in all-\nsolid-state cells?\n(Response) We thank the reviewer for raising these important points. The redox potentials of LZACO\nand their implications are now discussed in more detail on page 27: “The oxidation potential of 4.19\nV vs. Li/Li+ greatly surpasses not only those of sulfide solid electrolytes (no higher than 3 V vs. Li/Li+\n5,64), but also those of typical Zr-based (oxy)chloride solid electrolytes such as Li ZrCl and\n2 6\nLi ZrCl O (3.55 and 4.00 V vs. Li/Li+, respectively3), so LZACO should supposedly display\n1.75 4.75 0.5\nsuperior compatibility with the high-voltage cathodes. Besides, it has been reported that the\n(oxy)chloride solid electrolytes can generally form stable, Li-ion conductive interphases upon\noxidation, which allows for stable cycling to voltages beyond their oxidation potentials3,23,65-67.\nConsequently, the measured oxidation potential of 4.19 V vs. Li/Li+ entails that LZACO may direct\ncontact high-potential cathodes such as LiCoO and Ni-rich layered oxides in the all-solid-state cell,\n2\nwithout the need of any coating layer. On the other hand, the 1.62 V vs. Li/Li+ reduction potential of\nLZACO is lower than those of typical Zr-based (oxy)chlorides (2.16 and 1.79 V vs. Li/Li+ for Li ZrCl\n2 6\nand Li ZrCl O , respectively3), entailing better reduction stability. Regardless, the 1.62 V vs.\n1.75 4.75 0.5\nLi/Li+ reduction potential remains much higher than those of most energy-dense anodes. Furthermore,\nsince the final reduction products of LZACO would inevitably contain electronic conductors such as\nZr and Al, which cannot prevent the electrons needed for further reduction to migrate through, the\nreduction of this material is supposed to proceed continuously68,69. Such speculation is supported by\nthe Li | LZACO | Li and Li-In | LZACO | Li-In symmetric cells, both of which undergo a continuous\n18\nvoltage increase during cycling (Supplementary Fig. 15); in particular, the voltage of the Li | LZACO\n| Li cell reaches around 2 V after only 80 h of cycling at 0.1 mA cm2 (1 h per cycle). Therefore, to\nensure the stable cycling of the all-solid-state cell, LZACO needs to be separated from the anode by a\nlayer of more anode-compatible solid electrolyte such as LPSCl.”.\n(13) The performance of cells with LiCoO2 and scNCM92 cathodes. How do the initial discharge\ncapacities and Coulombic efficiencies of these cells compare to those reported in the literature for\nsimilar configurations?\n(Response) We are grateful to the reviewer’s valuable queries. The initial discharge capacities and\nCoulombic efficiencies of other reported cells with similar configurations are now compared with those\nof the LZACO-based cells in Supplementary Tables 23. It was found that LZACO can indeed enable\nsuperior cell performance.\nSupplementary Table 2. Comparison of the initial discharge capacity and Coulombic efficiency\nbetween the LZACO-based cell in Fig. 4a and those with the similar cell configuration.\nSpecific current Initial discharge capacity Coulombic\nCAM Catholyte Ref.\n(mA g−1) (mAh g−1) efficiency\nLCO LZACO 31.6 (0.2 C) 152.6 97.26% This work\nLCO Li1.75ZrCl4.75O0.5 79 (0.5 C) 145.6 97.73% (3)\nLCO Li3.4ZrCl4.6O1.4 14 (0.1 C) 160.9 97.3% (45)\nLCO Li5/3Cr1/3Zr1/3Cl4 ~31.6 (0.2 C) 108.2 96.09% (70)\nLCO Li2ZrCl6 14 (0.1 C) 137 97.9% (47)\nLCO Li3ZrCl4O1.5 70 (0.5 C) ~113.5 94.7% (25)\nLCO LiNbOCl4 ~14 (0.1 C) ~125 95% (21)\nLCO Li3ScCl6 ~14.6 (0.1 C) 126.2 90.3% (50)\nSupplementary Table 3. Comparison of the initial discharge capacity and Coulombic efficiency\nbetween the LZACO-based cell in Fig. 4d and those with the similar cell configuration.\nSpecific current Initial discharge capacity Coulombic\nCAM Catholyte Ref.\n(mA g−1) (mAh g−1) efficiency\nLiNi0.92Co0.06Mn0.02O2 LZACO 20 (0.1 C) 180.8 90.27% This work\nLiNi0.88Co0.11Al0.01O2 Li2ZrCl6 ~24 (0.1 C) 206 85.8% (49)\nLiNi0.5Co0.2Mn0.3O2 Li3Zr2Si2PO12 15 (0.1 C) 162 85.8% (74)\nLiNi0.5Co0.2Mn0.3O2 Li3PW12O40 ~15 (0.1 C) 165.6 98.1% (57)\n(14) LZACO is the only solid electrolyte with sufficiently low cost for commercialization that can\nenable stable cycling at a rate as high as 10 C. How was this cost-effectiveness determined, and what\nfactors contribute to its competitiveness compared to other solid electrolytes?\n(Response) We thank the reviewer for raising this important point. The method for determining the\ncost is described on page 44: “The cost per unit volume of the solid electrolyte for discussion here is\ncalculated by multiplying the cost per unit mass of the solid electrolyte and the density of the solid\nelecrolyte. While the method of density measurement has already been described in the “Structure and\nmorphology characterizations” section above, the cost per unit mass of the solid electrolyte was\ncalculated straightforwardly from the average market prices of the corresponding raw materials as the\nindustrial commmodity chemicals in the year of 2024. These prices and the information sources are\nlisted in Supplementary Table 1.”.\nSupplementary Table 1. Average market prices of the industrial commodity chemicals in 2024 and\nthe sources from which these prices are acquired.\nAverage market price in 2024\nCommodity chemical Sources\n($ kg1)\nLi2O 210.67 LB Group Co., Ltd.\nShandong Hongyang Chemical\nLiCl 14.04 Co., Ltd.\nChengxin Lithium Group Co.,\nLi2CO3 12.64\nLtd.\nCBC Metal\nZrCl4 11.24\n(https://www.cbcie.com/)\nAsian Metal\n(https://www.asianmetal.cn/)\nAlCl3 0.84\nShanghai Metals Market\n(https://www.smm.cn/)\nThe factors contributing to the cost-effectiveness are discussed on page 23: “These data suggest that\nhigh-quality LZACO can be synthesized from the cost-effective Li CO , ZrCl , and AlCl , whose\n2 3 4 3\n20\naverage market prices in 2024 as the industrial commodity chemicals are $12.64 kg1, $11.24 kg1, and\n$0.84 kg1, respectively (Fig. 3d and Supplementary Table 1). Based on these chemical prices and the\ndensity of LZACO (measured to be 2.15 g cm3; detailed procedure described in Methods), the raw\nmaterials cost of this solid electrolyte can be estimated as $22.77 L1 (Fig. 3e). In comparison, if the\nmuch more expensive Li O ($210.67 kg1), instead of the Li CO with $12.64 kg1 cost, is used to\n2 2 3\nsynthesize LZACO, the raw materials cost would be $92.94 L1, which is over four times that of the\nLi CO -synthesized LZACO ($22.77 L1, as mentioned above) and also greatly exceeds the $46.75\n2 3\nL1 solid-electrolyte raw materials cost for enabling reasonable ASSLB cost. Therefore, the fact that\nLZACO may be synthesized directly from the affordable Li CO is crucial to the cost-effectiveness of\n2 3\nthis solid electrolyte. In addition, since the synthesis of LZACO involves the rather cost-effective AlCl\n3\n($0.84 kg1) but does not rely on the relatively expensive LiCl ($14.04 kg1), its raw materials cost is\nalso lower than those of other previously reported Zr-based (oxy)chloride solid electrolytes (Fig. 3e).”.\n600\n400\n200\n0\n270 290 310 330 10 20 30 40 50 60 70 80 0 200 400 600\nFig. 3 | Cost-effectiveness of LZACO. a Electron energy-loss spectra of the LZACO synthesized\nusing Li CO , ZrCl , and AlCl as the raw materials. For comparison, the C-K spectrum of CaCO is\n2 3 4 3 3\nalso displayed. b XRD pattern of the LZACO synthesized using Li CO , ZrCl , and AlCl as the raw\n2 3 4 3\nmaterials. c Nyquist plot of the LZACO synthesized using Li CO , ZrCl , and AlCl as the raw\n2 3 4 3\nmaterials. The measurement was conducted at 25 C. d Average market prices in 2024 for the industrial\ncommodity chemicals involved in the cost estimation. e Raw materials costs of LZACO and two other\nrepresentative Zr-based (oxy)chloride solid electrolytes, Li ZrCl and Li ZrCl O .\n2 6 1.75 4.75 0.5\n(15) The performance of LZACO-based pouch cells. How do the mechanical properties of LZACO\ncontribute to the fabrication and performance of these pouch cells?\n(Response) We thank the reviewer for this thoughtful inquiry. The influence of the mechanical\nproperties of LZACO on the fabrication and performance of the pouch cells is now discussed on page\n21\n)mc\nW(\n''Z-\nc\ns25 C = 2.59 mS cm1\nZ' (W cm)\n215\n210\n205\n10\n5\n0\n)1-gk\n$(\necirp\ntekram\negareva\n4202\n60\n$210.67 kg-1\n40\n$14.04 kg-1 $12.64 kg-1\n$11.24 kg-1\n20\n$0.84 kg-1\n)1-L\n$(\ntsoc\nslairetam\nwaR\n$46.75 L-1\n$30.68 L-1\n$24.70 L-1\n$22.77 L-1\nLiCl Li2CO3 ZrCl4 AlCl3 Li2ZrCl6 Li1.75ZrCl4.75O0.5 LZACO\n).u.a(\nytisnetnI\nb\nLZACO synthesized using Li2CO3\nC2/m Li3ScCl6 (ccp)\nP3m1 Li2ZrCl6 (hcp)\n2q (degree)\n).u.a(\nytisnetnI\na\nLZACO synthesized using Li2CO3\nCaCO3\nC-K\nEnergy Loss (eV)\nd e\n32: “It should be noted that the superior mechanical compliance for the solid electrolyte has also been\nfound crucial to the fabrication of high-quality films for pouch cells. The compliant solid electrolytes\nsuch as the sulfides and halides may easily form and maintain the intimate solid-solid contact with the\nassistance of the polytetrafluoroethylene (PTFE) binder; instead, if the solid electrolyte is barely\ncompliant like the brittle oxide solid electrolytes, the films cannot enable meaningful cell performance\nwithout the addition of minor liquid electrolyte, due to the poor solid-solid contact75. Thanks to the\nhigh mechanical compliance of LZACO, the preparation of films for pouch cells are rather convenient.\nBoth the composite cathode films and the individual solid-electrolyte films can be easily prepared in\nrelatively large sizes, as shown in Fig. 5cd and Supplementary Fig. 18. Without the addition of any\nliquid electrolyte, the Li | LPSCl-LZACO | scNCM92 pouch cell formed by such films demonstrates\na reversible capacity of about 160.8 mAh g1 under 20 mA g1 (0.1 C) at 30 C (Fig. 5e).”.\nSupplementary Fig. 18. a LZACO film prepared by the dry-film technology. be Composite cathode film (b),\nLZACO film (c), LPSCl film (d), and Li metal anode (e) for all-solid-state pouch cells. The composite cathode\nfilm, LZACO film, and LPSCl film are all prepared by the dry-film technology.\n(16) The performance of LZACO-based cells at low stacking pressures. How does the mechanical\ncompliance of LZACO enable decent performance under these conditions, and what advantages does\nthis offer for practical applications? What potential improvements could be made to further enhance\nthe low-pressure cell performance, and how might these improvements impact the overall usability of\nLZACO?\n(Response) We sincerely appreciate the reviewer’s perceptive questions. The reason why the\nmechanical compliance of LZACO may enable decent low-pressure cell performance, along with the\nadvantage of this characteristic for practical applications, is discussed on page 36: “The high\nmechanical compliance of this material allows it to efficiently alter the morphology to accommodate\n22\nthe volume change of the CAM particles even under limited stresses. If the solid electrolytes employed\nare all highly compliant like LZACO, the ASSLBs do not have to operate under the impractically high\nstacking pressures above 100 MPa. In this way, the heavy instrument used to generate such pressures\n(e.g., the mold used for laboratory testing) is no longer needed, so that the ASSLB may eventually\nachieve decent energy densities for practical application.”.\nThe potential improvements that could be made to improve the low-pressure cell performance and the\nassociated impact on the overall usability of LZACO are discussed on page 37: “Furthermore, it should\nalso be noted that the low-pressure cell performance achieved here still has very large room for\nimprovement, because, due to the poor reduction stability of LZACO (reduction potential 1.62 V vs.\nLi/Li+, as shown in Supplementary Fig. 14), the anolyte of the cell above is still the commonly used\nLPSCl, which is much less compliant than LZACO (as shown in Fig. 2a) and thus unlikely to perform\nwell at low stacking pressures. If an anode-compatible solid electrolyte that is as compliant as LZACO\ncan be developed in the future, the low-pressure cell performance similar to those at high stacking\npressures should be achievable. To this end, the interphase resulting from the reduction of the solid\nelectrolyte must be electron-blocking, so that the electrons needed for further reduction cannot migrate\nthrough to reach the unreacted solid electrolyte79. Considering that the Zr4+ and Al3+ in LZACO would\ninevitably be reduced into electronic conductors such as Zr and Al by Li metal80,81, the presence of\nsuch metal cations should preferably be eliminated in the material. Instead, the solid electrolyte needs\nto be populated by non-metal cations such as P5+ and B3+, which will only be reduced into electron-\nblocking species79. If desirable mechanical compliance and ionic conductivity can be realized in such\nmaterials through rational materials design too, the cost-effective ASSLBs that can operate at\nsufficiently low stacking pressures for practical application may be expected.”.\nThis paper reports Li2O-ZrCl4-AlCl3 solid electrolytes exhibiting ionic conductivity of ~2.2 mS/cm\nand its cost-effective synthesis using Li2CO3 as a precursor. ASSBs using these solid electrolytes as\nthe catholyte are demonstrated. The finding is technically important, however, the novelty of this work\nis not enough to satisfy the high standard of Nat. Commun. Rather this work is worth to be reported in\nother more specialized journals.\nAs for novelty, many oxy-halide SEs exhibiting mS/cm-class ionic conductivity have been reported (e.g.\nLiNbOCl4, LiAlCl2.5O0.75, many Li-Zr-Cl-O compounds, xLi2O-MCly (M = Ta, Hf)) while many of\nthose previous reports already highlighted the role of amorphous matrix for achieving high ionic\nconductivity. Compare to the previous papers on oxy-halide SEs, this work does not provide new\nscientific insights in terms of material characterization, structure-property relation, or performances.\n(Response) We sincerely thank the reviewers for the careful assessment of our manuscript and the\nvaluable critiques, which offer us essential guidance for improvements. Regarding the reviewer’s\nconcern on novelty, we would like to emphasize that ionic conductivity is not the only metric for the\nadvantage of solid electrolytes; as mentioned in Introduction, the mechanical compliance is equally\nimportant. In this aspect, the LZACO material reported here achieves the hardness and Young’s\nmodulus considerably lower than those of other widely studied solid electrolytes (hardness: 0.22 vs. \n1.19 GPa; Young’s modulus: 1.41 vs.  7.92 GPa), demonstrating a superior mechanical compliance\n(Fig. 2a). With such a desirable characteristic, the LZACO may enable the construction of all-solid-\nstate cells that even outperform those based on more Li-ion conductive solid electrolytes, as compared\ncomprehensively in Supplementary Tables 28. We believe this exceptional mechanical compliance\nand the superior cell performance it can lead to endow the LZACO material with significant novelty.\nWe apologize for not presenting this point clearly enough in the original submission. In the revised\nmanuscript, we added one paragraph to emphasize it on page 39: “In addition to the decent cell\nperformance, the data above also demonstrate one crucial point: the importance of the mechanical\ncompliance for solid electrolytes. In the discussion above, the all-solid-state cells formed by LZACO\nare compared with those based on other solid electrolytes when different CAMs, CAM mass loadings,\ncycling conditions, etc., are employed (Supplementary Tables 28). Among all the solid electrolytes\ninvolved in such comparison, LZACO is in fact not the one with the highest ionic conductivity.\nRegardless, the cell constructed by LZACO can still outperform those based on other more Li-ion\nconductive solid electrolytes. The superior mechanical compliance of LZACO (0.22 GPa hardness and\n1.41 GPa Young’s modulus, as shown in Fig. 2a) plays a pivotal role here. In fact, when the ionic\nconductivity of the solid electrolyte exceeds 1 mS cm1, improving its mechanical compliance should\nbe more effective in optimizing the cell performance than further increasing the ionic conductivity,\nas the bottleneck of the overall ion transport has shifted from the interior of the solid electrolyte to the\ninterfacial contact between different cell components. Under such circumstances, if the cell employs\nhighly compliant solid electrolytes such as LZACO, it can more easily achieve and maintain the\nintimate solid-solid contact, thereby effectively improving the overall ion transport efficiency. From\nthis perspective, the discovery of the mechanically compliant LZACO has pointed out an effective\nentry point for further optimizing the comprehensive performance of the solid electrolytes that are\n24\nalready highly Li-ion conductive.”.\nThe change of XRD patterns of LZACO after annealing should be discussed in detail. After 100 oC\nannealing, it seems to transform to the trigonal structure than it decomposed with the appearance of\nLiCl?\n(Response) We thank the reviewer for raising this important point. When the crystallinity is as low as\nthe LZACO materials studied here, the XRD cannot actually distinguish LiCl from the C2/m structure\nthat had been observed in many (oxy)chloride solid electrolytes. Therefore, although the Bragg\nreflections resembling those of LiCl are present as noted by the reviewer, it does not necessarily\nindicate the existence of LiCl. Considering that the low crystallinity prevents the conclusive crystal\nstructure determination and that both the LiCl and the C2/m structure mentioned above show cubic\nclose-packed (ccp) anion configuration, we follow the suggestion from the other reviewer (Reviewer\n#1, Question 2) to refer to this phase more generally as the “ccp phase”, instead of designating a\ndefinitive crystal structure. Similarly, the specific structure of the “trigonal” phase noted by the\nreviewer cannot be conclusively determined either, and the only thing for sure is its hexagonal close-\npacked (hcp) anion configuration. Therefore, this phase is referred to as the “hcp phase” in the revised\nmanuscript. The structural evolution noted by the reviewer is in fact the change of the molar ratio\nbetween the ccp and hcp phases after annealing. Since these two phases originally coexist in the as-\nsynthesized LZACO, they must be energetically comparable in this material. Consequently, minor\nenergy disruption such as that induced by the 100 C annealing is supposed to slightly vary their molar\nratio. However, such annealing does not considerably improve the crystallinity, so the material is still\ndominated by the highly Li-ion conductive amorphous species. This point is clarified on page 12: “To\ndemonstrate this point, we annealed LZACO at 100 C for 5 h, and probed the associated change of\nthe XRD pattern and ionic conductivity. As shown in Supplementary Fig. 8a, the content of the hcp\nphase appears to increase slightly with respect to that of the ccp phase after annealing; as the two\ncoexisting phases in LZACO, the hcp and ccp phases must be energetically comparable in this material,\nso a relatively low energy input, such as that associated with the 100 C annealing, should be sufficient\nto alter the ratio between them. Regardless, both of these crystalline phases are still present after\nannealing, and, more importantly, they continue to occupy a negligibly small fraction in LZACO, as\nindicated by the diffuse Bragg reflections in the XRD pattern (Supplementary Fig. 8a). Since the\nmajority of LZACO remains the highly Li-ion conductive amorphous species, the material still\nmaintains a high ionic conductivity of 2.23 mS cm1 at 25 C, almost identical with that before\nannealing (2.55 mS cm1 at 25 C), as shown in Supplementary Fig. 8b.”\nIt is recommended to examine air- and dry-room stability of LZACO to estimate its availability in a\npractical cell manufacturing process.\n(Response) We sincerely thank the reviewer for this constructive suggestion. While the humidity\ntolerance test in our original submission was conducted in air using an environmental chamber, in the\nrevised manuscript we also supplemented the testing results in a dry room. The data and discussion are\npresented on page 24: “Besides, decent humidity tolerance was observed in the dry room too. When\nthe LZACO powder was exposed to a dry room with the relative humidity of 3.85% (dew point set as\n20 C) at 25 C for 12 h, the XRD pattern and ionic conductivity do not undergo considerable change\n25\neither (Supplementary Fig. 13).”.\n1200\n800\n400\n0\n10 20 30 40 50 60 70 80 0 400 800 1200\nSupplementary Fig. 13. Humidity tolerance test conducted in a dry room. a XRD patterns of the LZACO\npowders before and after exposure to the air with 3.85% relative humidity at 25 C. b Nyquist plots of LZACO\nbefore and after exposure to the air with 3.85% relative humidity at 25 C. The exposure experiment was\nconducted using the powder samples, while the EIS measurements were conducted on the pellets prepared by\ncold pressing the exposed or non-exposed powders under 300 MPa, at 25 C.\n26\n).u.a(\nytisnetnI\na\n3.85% relative humidity, 12 h (dry room)\nNon-exposed\n3.85% relative humidity\n12 h (dry room)\nNon-exposed\n2q (degree)\n)mc\nW(\n''Z-\nb\nLZACO\n2.59 ´ 103 S cm1\n1.55 ´ 103 S cm1\nLZACO\nZ' (W cm)\nc d\nReviewer #4 (Remarks to the Author):\nThis study emphasizes the critical role of mechanical compliance in solid electrolytes for all-solid-\nstate batteries, alongside ionic conductivity and cost. In this regard, the authors introduces xLi2O-(1-\ny)ZrCl4-yAlCl3 (LZACO, x = 1.0 ~ 1.8, y = 0.2 ~ 0.5) as a novel oxychloride electrolyte with\nremarkably low hardness (0.22 GPa) and Young’s modulus (1.41 GPa), targeting commercialization\nviability. LZACO is synthesized via mechanochemical milling of Li2CO3, ZrCl4, and AlCl3, achieving\nan ionic conductivity of 2.55 mS cm−1 at 25°C through amorphous-phase dominance. The authors\nestimated that the cost of raw material is using a log-log scaling model, with Li2CO3 replacing costly\nLi2O. Given the result from cost modeling, the authors suggest the low cost of raw material of $10.61\nkg−1 for LZACO by substituting Zr4+ and Al3+ for Ta5+ from 1.6Li2O-TaCl5 and replacing Li2O to\nLi2CO3 for synthesis. The synthesized LZACO exhibits superior deformability compared to\nsulfide/halide electrolytes and the phase-field modeling further supports the important of low hardness\nand Young’s modulus. The authors demonstrated the effect of improved mechanical compliance of\nLZACO by showing long term cycling of all-solid-state batteries using LiCoO2 and NCM92 cathodes\nachieving 3.62–3.92 mAh cm−2 areal capacity (85–90% retention after 100 cycles) at 25°C. While the\nauthors demonstrate the excellent electrochemical properties of LZACO in all solid state batteries\n(ASSBs), I believe this paper ultimately falls short of the requirements for publication in nature\ncommunications for the reasons articulated below.\n1. Page 6, line 2: The authors propose a chemical price threshold of $50 kg⁻¹ for the commercialization\nof ASSBs. However, this paper provides no supporting evidence for this value, nor do the references\ncited offer any justification. To substantiate this claim, the authors should present a comprehensive\nmarket analysis, including data from at least the past two years, as well as a universal framework for\nestimating the chemical cost associated with ASSB commercialization.\n(Response) We are deeply grateful to the reviewer for his/her thorough review and insightful feedbacks;\nthe constructive suggestions he/she raised are highly valuable for improving our work. Although the\n$50 kg1 solid-electrolyte cost has been referred to as the threshold for commercializing all-solid-state\nbatteries in the studies from different research groups recently, there is indeed no direct evidence\nsupporting this point in literature, as noted by the reviewer. Therefore, the meaning of this benchmark\nneeds to be carefully discussed. Fortunately, the kind of comprehensive, in-depth market analysis\nneeded for such a purpose has been published only a few months ago by Pasta et al. (Nature Energy\n10, 135–147, 2025), and they also assumed the solid-electrolyte cost to be the aforementioned $50 kg1\nfor estimation. Interestingly, under this assumption, the all-solid-state batteries with the energy-dense\nLi metal anode still cost more than that of the commercial liquid-state Li-ion batteries ($158 kWh1 vs.\n$126 kWh1); in particular, even if the solid electrolyte is assumed free, the cost of all-solid-state\nbatteries in such comprehensive estimation is still higher ($134 kWh1). Under this circumstance,\nwhether the all-solid-state batteries can be successfully commercialized depends on whether its energy-\ndensity and safety advantages can justify the relatively high cost in the market, and this is very difficult\nto definitively predict for now. In other words, the $50 kg-1 solid-electrolyte cost only leads to a\nrelatively reasonable all-solid-state batteries production cost with potential commercial viability;\nit cannot guarantee a lower cell production cost than those of commercial Li-ion batteries.\nreasonable cell production cost of $158 kWh1 is based on the assumption that the solid electrolyte is\nLi P S . If other solid electrolytes were used, the mass of the solid electrolyte needed to reach the\n7 3 11\nsame solid-electrolyte volume fraction in the composite cathode and the same solid-electrolyte layer\nthickness would be different. Under such circumstances, the $50 kg1 solid-electrolyte cost might no\nlonger lead to reasonable cell production costs like $158 kWh1. Clearly, the cost per unit mass of the\nsolid electrolyte is not the ideal metric for discussing the cost-effectiveness of solid electrolytes,\nas the desired values for different solid electrolytes are different. In comparison, the cost per unit volume of\nthe solid electrolyte might be more suitable for this purpose; the optimal solid-electrolyte volume in\neach kWh of batteries (depending on the optimal solid-electrolyte volume fraction in the composite\ncathode and the optimal solid-electrolyte layer thickness) does not vary with the type of the solid\nelectrolyte, so the desired cost per unit volume of the solid electrolyte for a given cell configuration\nwould be the same for all the solid electrolytes, which makes it a more appropriate metric for\ncomparison. In the cell configuration used in the aforementioned study (adapted from the batteries in\nVolkswagen ID. 3; Nature Energy 10, 135–147, 2025), the $50 kg1 gravimetric solid-electrolyte cost\nassumed for Li P S , a material with the density of 1.870 g cm3, can be easily converted to the\n7 3 11\nvolumetric solid-electrolyte cost of $93.50 L1. Considering that the processing cost of the solid\nelectrolytes cannot be precisely predicted due to the uncertainty of the method for mass production,\nwe assume the processing cost of solid electrolytes will not exceed 50% of their total costs, which is\nalso the situation of most chemicals in the Li-ion battery industry. In this way, in order to ensure the\nsolid-electrolyte cost below $93.50 L1, the raw materials cost of the solid electrolyte must not exceed\n$46.75 L1. In the revised manuscript, this $46.75 L1 solid-electrolyte raw materials cost is used as\nthe reference for discussion, and, as mentioned above, we particularly emphasized that this only leads\nto a relatively reasonable cell production cost, instead of guaranteeing lower costs than those of\ncommercial Li-ion batteries. Once again, we sincerely thank the reviewer for helping us clarify this\nissue, which has been confusing us and probably other researchers for long.\nThe contents above are presented in the “Cost-effectiveness” section, on page 21: “In many recent\nstudies, the $50 kg1 solid-electrolyte cost is referred to as the threshold for the successful\ncommercialization of ASSLBs3,38,57, but this standard is in fact questionable. First and foremost, the\nsolid-electrolyte cost below $50 kg1 cannot actually ensure that the total production cost of ASSLBs\nlies below those of commercial Li-ion batteries. Recently, Pasta et al. have conducted an in-depth cost\nstudy based on a comprehensive market analysis58. Using the actual cell parameters for the batteries in\nVolkswagen ID. 3, they compared the cost of the energy-dense ASSLBs and the commercial liquid-\nstate Li-ion batteries. Such calculations suggest that the ASSLBs with the aforementioned $50 kg1\nsolid-electrolyte cost is still more expensive than the commercial Li-ion batteries ($158 kWh1 vs.\n$126 kWh1). In particular, even if the solid electrolyte is assumed free, the ASSLBs still cost $134\nkWh1, exceeding the $126 kWh1 cost for commercial Li-ion batteries. Under this circumstance, the\ncommercial viability of the ASSLBs depends on whether their energy-density and safety advantages\ncan justify such high costs in the market, but this cannot be predicted definitively for now. That is, the\n$50 kg1 solid-electrolyte cost should by no means be regarded as a threshold guaranteeing an ASSLB\ncost that is lower than those of commercial Li-ion batteries; instead, it is merely a cost that may yield\nrelatively reasonable ASSLB cost, with potential commercial viability. Additionally, compared with\nthe cost per unit mass like the $50 kg1 discussed above, the cost per unit volume should be more\n28\nappropriate for discussing the cost-effectiveness of solid electrolytes. In all-solid-state batteries, the\noptimal amount of the solid electrolyte is not actually defined by the mass, but by the volume: the\ncomposite cathode with the optimal tortuosity needs the solid electrolyte to occupy a certain volume\nfraction, while the balance between energy density and safety is realized by adjusting the thickness of\nthe solid-electrolyte layer. Consequently, no matter what kind of solid electrolyte is employed, the\noptimal solid-electrolyte volume in each kWh of batteries would be the same. On this basis, as long as\nthe cost per unit volume of the solid electrolyte is determined, the solid-electrolyte cost per kWh of\nbatteries, i.e., the ultimate metric for the cost-effectiveness of solid electrolytes, is determined too.\nTherefore, compared with the widely discussed cost per unit mass of the solid electrolyte, the cost per\nunit volume of the solid electrolyte is more suitable for discussion. In the aforementioned study by\nPasta et al., the solid electrolyte is assumed to be Li P S , so, using the density of 1.870 g cm359 for\n7 3 11\nthis material, it can be easily found that the $50 kg1 gravimetric solid-electrolyte cost that may enable\nrelatively reasonable cell production cost corresponds to a volumetric solid-electrolyte cost of $93.50\nL1. Here, it should be noted that such a $93.50 L1 cost includes both the raw materials cost and the\nprocessing cost. Considering that the method for the mass production of solid electrolytes has not been\nfinally determined, the processing cost cannot be accurately estimated. Regardless, if assuming the\nprocessing costs of the solid electrolyte is no higher than 50% of its total cost, like most of the other\nchemicals involved in Li-ion batteries58,60, it can be found that, to ensure the solid-electrolyte cost\nbelow $93.50 L1, the raw materials cost of the solid electrolyte must not exceed $46.75 L1. In the\ndiscussion below, this will be regarded as the raw materials cost of the solid electrolyte that can enable\nrelatively reasonable costs for ASSLBs.”.\n2. Supplementary table 1 and 2: The authors present laboratory-scale chemical prices for solid\nelectrolyte fabrication in Supplementary Tables 1 and 2. However, these prices are derived solely from\ntwo chemical suppliers, Alfa Aesar and Aladdin, and are limited to data from January 2025. Relying\non arbitrarily selected suppliers over such a narrow timeframe undermines the credibility of the\neconomic and scientific analysis. A broader dataset encompassing multiple suppliers and a longer time\nperiod is necessary to provide a robust evaluation.\n(Response) We thank the reviewer for this insightful suggestion. The prices that are more\nrepresentative of the actual situations are indeed needed. Following the reviewer’s suggestion, we\ncease to use the prices inferred from the laboratory-scale chemicals, but utilize the average market\nprices of the corresponding industrial commodity chemicals in the year of 2024 (the information\nsources are specified along with the prices in Supplementary Table 1, which is also displayed below).\nIt should be noted that the raw materials of some widely studied solid electrolytes, such as the high-\npurity Li S needed for fabricating Li PS Cl, are not yet available as the bulk industrial commodities;\n2 5 6\nthis is also one of the major reasons why they are too expensive to commercialize for now. In light of\nthis fact, we no longer compare the costs of such solid electrolytes in the revised manuscript. Instead,\nour comparison focuses only on the Zr-based (oxy)chloride solid electrolytes, whose raw materials are\nall available as industrial commodity chemicals. The related discussion is made on page 23: “These\ndata suggest that high-quality LZACO can be synthesized from the cost-effective Li CO , ZrCl , and\n2 3 4\nAlCl , whose average market prices in 2024 as the industrial commodity chemicals are $12.64 kg1,\n3\n$11.24 kg1, and $0.84 kg1, respectively (Fig. 3d and Supplementary Table 1). Based on these\nchemical prices and the density of LZACO (measured to be 2.15 g cm3; detailed procedure described\n29\nin Methods), the raw materials cost of this solid electrolyte can be estimated as $22.77 L1 (Fig. 3e).\nIn comparison, if the much more expensive Li O ($210.67 kg1), instead of the Li CO with $12.64\n2 2 3\nkg1 cost, is used to synthesize LZACO, the raw materials cost would be $92.94 L1, which is over\nfour times that of the Li CO -synthesized LZACO ($22.77 L1, as mentioned above) and also greatly\n2 3\nexceeds the $46.75 L1 solid-electrolyte raw materials cost for enabling reasonable ASSLB cost.\nTherefore, the fact that LZACO may be synthesized directly from the affordable Li CO is crucial to\n2 3\nthe cost-effectiveness of this solid electrolyte. In addition, since the synthesis of LZACO involves the\nrather cost-effective AlCl ($0.84 kg1) but does not rely on the relatively expensive LiCl ($14.04 kg1),\n3\nits raw materials cost is also lower than those of other previously reported Zr-based (oxy)chloride solid\nelectrolytes (Fig. 3e).”.\n600\n400\n200\n0\n270 290 310 330 10 20 30 40 50 60 70 80 0 200 400 600\nFig. 3 | Cost-effectiveness of LZACO. a Electron energy-loss spectra of the LZACO synthesized\nusing Li CO , ZrCl , and AlCl as the raw materials. For comparison, the C-K spectrum of CaCO is\n2 3 4 3 3\nalso displayed. b XRD pattern of the LZACO synthesized using Li CO , ZrCl , and AlCl as the raw\n2 3 4 3\nmaterials. c Nyquist plot of the LZACO synthesized using Li CO , ZrCl , and AlCl as the raw\n2 3 4 3\nmaterials. The measurement was conducted at 25 C. d Average market prices in 2024 for the industrial\ncommodity chemicals involved in the cost estimation. e Raw materials costs of LZACO and two other\nrepresentative Zr-based (oxy)chloride solid electrolytes, Li ZrCl and Li ZrCl O .\n2 6 1.75 4.75 0.5\nSupplementary Table 1. Average market prices of the industrial commodity chemicals in 2024 and\nthe sources from which these prices are acquired.\nAverage market price in 2024\nCommodity chemical Sources\n($ kg1)\nLi2O 210.67\nLB Group Co., Ltd.\n30\n)mc\nW(\n''Z-\nc\ns25 C = 2.59 mS cm1\nZ' (W cm)\n215\n210\n205\n10\n5\n0\n)1-gk\n$(\necirp\ntekram\negareva\n4202\n60\n$210.67 kg-1\n40\n$14.04 kg-1 $12.64 kg-1\n$11.24 kg-1\n20\n$0.84 kg-1\n)1-L\n$(\ntsoc\nslairetam\nwaR\n$46.75 L-1\n$30.68 L-1\n$24.70 L-1\n$22.77 L-1\nLiCl Li2CO3 ZrCl4 AlCl3 Li2ZrCl6 Li1.75ZrCl4.75O0.5 LZACO\n).u.a(\nytisnetnI\nb\nLZACO synthesized using Li2CO3\nC2/m Li3ScCl6 (ccp)\nP3m1 Li2ZrCl6 (hcp)\n2q (degree)\n).u.a(\nytisnetnI\na\nLZACO synthesized using Li2CO3\nCaCO3\nC-K\nEnergy Loss (eV)\nd e\nLiCl 14.04 Shandong Hongyang Chemical\nCo., Ltd.\nLi2CO3 12.64 Chengxin Lithium Group Co.,\nLtd.\nZrCl4 11.24\nCBC Metal\n(https://www.cbcie.com/)\nAsian Metal\nAlCl3 0.84 (https://www.asianmetal.cn/)\nShanghai Metals Market\n(https://www.smm.cn/)\n3. In addition to the chemical cost of solid electrolytes, the overall price of ASSBs is influenced by\nvarious hidden manufacturing expenses, such as synthesis processing fees, chemical maintenance costs,\nand others.\n(Response) We fully agree with the reviewer that the discussion of the solid-electrolyte cost needs to\nbe placed in the context of the overall battery cost. As mentioned above, based on the in-depth battery\ncost analysis reported recently by Pasta et al. (Nature Energy 10, 135–147, 2025), we inferred that the\n$46.75 L1 solid-electrolyte raw materials cost should lead to a relatively reasonable all-solid-state\nbattery cost with potential commercial viability. This is used as the reference for the cost analysis in\nthe revised manuscript.\nMoreover, material costs can fluctuate significantly during mass production for commercialization.\n(Response) The materials cost fluctuation is indeed an important factor that needs to be considered. As\nmentioned above, we follow the reviewer’s suggestion and utilize the average market prices of the\nindustrial commodity chemicals in 2024 to minimize the distraction from this factor.\nImportantly, LZACO requires co-utilization with sulfide-based solid electrolytes or Li-alloy anodes\ndue to its incompatibility with Li metal anodes, which reduces the energy density of ASSBs and\nincreases manufacturing costs.\n(Response) We thank the reviewer for raising this important point. The discovery of LZACO alone\nindeed cannot ensure the successful commercialization of all-solid-state Li batteries; it is only a\nrelatively affordable catholyte, but presently many other cell components, such as the anolyte and the\nenergy-dense anodes, remain rather expensive, as noted by the reviewer. Therefore, LZACO only\nmeets one of the many necessary but insufficient conditions for commercializing all-solid-state Li\nbatteries. We thank the reviewer for helping us clarify this important point. To avoid misleading the\nreaders, we emphasize it on page 25: “Although the data above are indicative of decent cost-\neffectiveness for LZACO, it must also be emphasized that this material alone cannot address the cost\nissue for the commercialization of ASSLBs. Similar to other Zr-based oxychloride solid electrolytes63,\nLZACO is not supposed to be compatible with the reductive anodes such as Li metal. Therefore, it\n31\nmay only serve as the catholyte, which still needs to be separated from the anode by the overly\nexpensive solid electrolytes such as the sulfides3. Besides, the thin Li metal foil needed to enable high\nenergy densities for ASSLBs is also too expensive to make the cost of ASSLBs equal to that of\ncommercial liquid-state batteries58. To endow ASSLBs with commercial viability, the cost of these\ncomponents must be lowered too. The identification of cost-effective catholytes such as LZACO only\nmeets one necessary but insufficient condition for addressing the cost issue of ASSLBs.”.\nConsequently, laboratory-scale chemical pricing alone is insufficient to convincingly demonstrate\nLZACO's advantages for ASSB commercialization.\n(Response) We fully agree with the reviewer that the laboratory-scale chemical pricing is not\nconvincing enough. As mentioned above, we utilized the market prices of the industrial commodity\nchemicals instead in the revised manuscript. Once again, we sincerely thank the reviewer for helping\nus improving the reliability of the cost analysis.\n4. Page 9, line 3-16: The authors attribute LZACO's high ionic conductivity to material amorphization,\nreferencing studies on Zr-based halide solid electrolytes. While \"intermediate compositions\" have been\nreported in prior research in references, the correlation between these compositions, amorphous\nphases in synthesized materials, and their impact on ionic conductivity remains unclear. As ball\nmilling-induced amorphization introduces atomic site disorder within materials, this phenomenon\nshould be thoroughly discussed in relation to its influence on LZACO's ion conductivity.\n(Response) We thank the reviewer for this insightful and constructive suggestion. The improved ionic\nconductivity should indeed be discussed from the perspective of atomic configurations, instead of only\nthe coexisting crystalline phases and “intermediate compositions”. In the revised manuscript, we made\nsuch discussion based on the X-ray absorption spectroscopy on page 11: “Although both LZACO and\nthe previously reported Li-Zr-Cl-O oxychlorides rely on the amorphous phase to realize fast Li-ion\ntransport, the specific atomic configurations in their amorphous phases are not the same, which leads\nto different ion transport efficiencies. In the Li-Zr-Cl-O oxychlorides, the averaged Zr-O and Zr-Cl\nbond lengths in the distorted Zr-O/Cl polyhedra are believed to be the key to the superior ion transport\nefficiency, as they flatten the energy landscape for Li-ion migration to lower the overall migration\nbarriers25. Such a disordered atomic arrangement also occurs in LZACO, but to a more pronounced\ndegree. To characterize this behavior, we conducted the X-ray absorption spectroscopy (XAS). As\nshown in Supplementary Fig. 7a, the Zr K-edge X-ray absorption near edge structure (XANES)\nspectrum of LZACO does not show distinct peaks like those of ZrO and ZrCl , but appears as a broad\n2 4\nhump, entailing that the Zr-Cl and Zr-O bond lengths in LZACO vary in a range, instead of displaying\ndefinitive values. On this basis, more interesting behaviors were observed in the Fourier transformed\nextended X-ray absorption fine structure (FT-EXAFS) spectra. Unlike other Li-Zr-Cl-O solid\nelectrolytes25, the Zr-O and Zr-Cl signals in LZACO are not distinguishable from each other, but nearly\nmerge into one broad peak (Supplementary Fig. 7b). This observation suggests that the Zr-O and Zr-\nCl bond lengths in LZACO distribute in a broader range than those in the Li-Zr-Cl-O solid\nelectrolytes25. Besides, the FT-EXAFS spectrum of LZACO almost shows no signals above 2.5 Å,\nentailing the absence of ordering with coherence length exceeding such a distance; in contrast, other\nLi-Zr-Cl-O solid electrolytes still display minor signals in this range25. Consistent results were\n32\nobserved in the phase-uncorrected wavelet transformed (WT) EXAFS spectrum too. While the Zr-O\nand Zr-Cl bonding still give rise to two distinct signals, respectively, in the Li-Zr-Cl-O solid\nelectrolytes25, they merge together in LZACO (Supplementary Fig. 7c). Besides, the Zr-Zr bonding at\nabout 3 Å in the WT-EXAFS spectra of typical Li-Zr-Cl-O solid electrolytes are absent in that of\nLZACO too (Supplementary Fig. 7c), confirming the absence of the ordering with such large\ncoherence lengths. These observations consistently suggest that LZACO shows a more disordered\natomic configuration than the previously reported Li-Zr-Cl-O solid electrolytes. As mentioned above,\nsuch more disordered state should supposedly favor fast Li-ion transport in Zr-based oxychlorides25,\nwhich explains the superior ionic conductivity of LZACO with respect to those of other Li-Zr-Cl-O\nsolid electrolytes (2.55 vs. 12 mS cm1 at 25 C25).”.\n17920 17990 18060 18130 18200 1 2 3 4 5\nSupplementary Fig. 7. a,b XANES (a) and FT-EXAFS (b) spectra of LZACO at the Zr K-edge. For\ncomparison, the spectra of ZrCl and ZrO are also presented. c WT-EXAFS contour plot of LZACO\n4 2\nat the Zr K-edge.\n5. The synthesis of amorphized Li₂ZrCl₆ solid electrolytes via anion substitution (e.g., Cl⁻ replaced by\nother anions) has already been extensively explored in previous studies (e.g., J. Cheng et al., Journal\nof Energy Storage, 2024, 89, 111700, D. Xu et al., J. Mater. Chem. A, 2024, 12, 27694, F. Hussain et\nal., npj Comput Mater, 2024, 10, 148, and etc.). Similarly, substituting Zr with Ta has been reported\n(e.g., X. Liu et al., Energy Storage Materials, 2024, 72, 103737 and etc.). Furthermore, the economic\nevaluation of oxyhalide solid electrolytes was addressed in earlier work (L. Hu, Nat Commun., 2023,\n14, 3807). While this paper provides additional insights into LZACO's mechanical properties, its lack\nof novelty regarding the material itself diminishes its overall contribution to the field.\n(Response) We deeply appreciate the reviewer’s valuable and thoughtful critique. In fact, it is the\nexistence of these similar compositions in literature that highlights the novelty and importance of our\ndiscovery. Prior to the present study, the Zr-based (oxy)chloride solid electrolytes such as Li ZrCl and\n2 6\nLi ZrCl O are commonly believed to display relatively poor mechanical compliance. In this\n1.75 4.75 0.5\ncontext, the present study discovers that one of this category of materials, LZACO, may in fact achieve\nthe mechanical compliance even greatly surpassing those of many widely studied solid electrolytes\n(Fig. 2a). In the meantime, other advantages of Zr-based (oxy)chloride solid electrolytes, such as the\ncost-effectiveness, relatively high ionic conductivity, oxidation stability, etc., are not compromised\neither. From this perspective, we believe the discovery of LZACO makes important contribution to the\nresearch field of all-solid-state batteries.\n33\n).u.a(\nnoitprosroba\ndezilaomroN\nLZACO\nZrO2\nPhoton energy (eV)\n)stinu\n.bra(\n|2k*)k(c\nTF|\nb c\n4\n3\n0\n0 5 10 15\nR (Å) k (Å-1)\n)Å(\nR\n+ R\na\nLZACO\nLZACO\nZrCl4\nZrO2 Zr-O/Cl\nZrCl4\nWe sincerely thank the reviewer for helping us clarify this point. In the revised manuscript, we\nemphasize it on page 19: “In summary, the computational and experimental data presented in Fig. 2\nabove consistently suggest that the LZACO solid electrolyte reported here is not plagued by the\nrelatively poor mechanical compliance in typical Zr-based (oxy)chloride solid electrolytes such as the\nLi ZrCl and LZCO for comparison above. On the contrary, the mechanical compliance of LZACO\n2 6\neven surpasses those of many widely studied sulfide and halide solid electrolytes, as shown in Fig. 2a.\nTherefore, although many derivatives and chemical modifications of Zr-based (oxy)chloride solid\nelectrolytes have already been reported in literature45,54-56, the LZACO material with the unique\nadvantage in mechanical compliance can still play a distinctive role in ASSLBs.”.\n6. The authors highlight the low Young’s modulus and hardness of LZACO as critical factors for stable\ncontact between LZACO and cathode active materials during ASSB cycling. However, their\nexperiments employed an impractically high stack pressure of 190 MPa with low cathode active\nmaterial loading of ~5.5 mg‧cm⁻², which fails to substantiate the mechanical compliance benefits of\nLZACO under realistic conditions. Furthermore, Figures 6 and 7 show that LZACO cells with high\ncathode loading of > 25 mg‧cm⁻² cycled at low stack pressure of 5 MPa do not outperform previously\nreported oxyhalide solid electrolytes in ASSBs in terms of capacity retention. A systematic comparison\nof stack pressure effects on ASSB cycling using LZACO versus other solid electrolytes such as LZCO\nor LZO would provide more compelling evidence for the importance of mechanical compliance.\n(Response) We sincerely thank the reviewer for this insightful suggestion. In the revised manuscript,\nthe low-pressure performance of the cell formed by LZACO was compared with those formed by\nLZCO and LZC, respectively. Besides, the comparison was also made with other cells operating at low\nstacking pressures in literature. It was found that the mechanical compliant LZACO indeed displays\nadvantages in this regard. The results are presented on page 36: “For comparison, we also tried to\nreplace the LZACO in the cells above with Li ZrCl (LZC) or LZCO (both are much less compliant\n2 6\nthan LZACO, as shown in Fig. 2a), and then conducted the cycling tests under the same conditions,\nespecially the low stacking pressure of 5 MPa. The variation tendency of the cell performance was\nfound consistent with that of the mechanical compliance disclosed in Fig. 2a. As shown in\nSupplementary Fig. 19, the least compliant LZC solid electrolyte results in the poorest cycling\nperformance; the capacity retention after 100 cycles is only 51.09%. In comparison, the relatively more\ncompliant LZCO enables better cycling stability, with the capacity retention being 69.21% after 100\ncycles. As for LZACO, its mechanical compliance greatly exceeds those of both LZC and LZCO (Fig.\n2a), so this material enables the most stable cycling performance; after 100 cycles, the capacity\nretention is 91.52%. In addition to the two typical Zr-based (oxy)chloride solid electrolytes for\ncomparison above, the mechanically compliant LZACO can also enable better cell performance than\nmany other widely studied solid electrolytes. As shown in Supplementary Table 8, the cycling\nperformance achieved by the LZACO-based cells at 5 MPa even surpasses that of certain cells at higher\npressures such as 10 MPa11,35,78. These observations demonstrate the advantage of the mechanically\ncompliant LZACO in enabling decent cell performance at low stacking pressures, which is a\nprerequisite for constructing practical ASSLBs”.\n34\n240\n180\n120\n60\n0 20 40 60 80 100\nSupplementary Fig. 19. a−c Long-term cycling performance of the Li Si | LPSCl-LZC | scNCM92\n13 4\ncell (a), Li Si | LPSCl-LZCO | scNCM92 cell (b), and Li Si | LPSCl-LZACO | scNCM92 cell (c)\n13 4 13 4\nunder 5 MPa at 30 C.\nSupplementary Table 8. Low-pressure cycling performance of the LZACO-based ASSLBs and those\nbased on other solid electrolytes.\nSpecific\nStacking\nTemperature\nCAM Catholyte current Capacity retention Ref.\npressure\n(C)\n(mA g−1)\n(MPa)\n95% (69 cycles)\nLiNi0.92Co0.06Mn0.02O2 LZACO 30 5 90% (119 cycles)\n(0.33 C) work\n80% (215 cycles)\n35\n)1-g\nhAm(\nyticapaC\nc\n100\n91.52% capacity retention 90\n(100 cycles)\nDischarge 30 C, 66 mA g-1 (0.33 C), 5.29 mg cm-2\n2.0 ¾ 4.3 V vs. Li/Li+\n)%(\nycneiciffe\ncibmoluoC\n180\n135\n90\n45\n0\n0 20 40 60 80 100\n200\n150\n100\n50\n0\n0 20 40 60 80 100\nCoulombic efficiency\n)1-g\nhAm(\nyticapaC\nb\n100\n90\n69.21% capacity retention 80\n(100 cycles)\n2.0 ¾ 4.3 V vs. Li/Li+\n)%(\nycneiciffe\ncibmoluoC\nCoulombic efficiency\n)1-g\nhAm(\nyticapaC\na\n100\n90\n80\n51.09% capacity retention\n(100 cycles) 70\nCharge Li13Si4 | LPSCl-LZC | scNCM92 60\nDischarge 30 C, 66 mA g-1 (0.33 C), 5.17 mg cm-2\n2.0 ¾ 4.3 V vs. Li/Li+\n)%(\nycneiciffe\ncibmoluoC\nCoulombic efficiency\n~70\nLiCoO2 Li1.625Al0.375Zr0.625Cl5.25 30 9.62 ~58.71% (282 cycles) (78)\n(0.5 C)\n~70\nLiCoO2 Li2ZrCl6 30 9.62 ~48.74% (109 cycles) (78)\n(0.5 C)\n2 65% (50 cycles) (35)\nLiNi0.83Co0.11Mn0.06O2 Li3InCl6 n/a 80\n10 93% (50 cycles) (35)\n~66\nLiNi0.5Co0.2Mn0.3O2 Li0.388Ta0.238La0.475Cl3 30 ~2 81.6% (100 cycles) (11)\n(0.44 C)\nUnless otherwise specified, all page numbers, figure numbers, and reference numbers mentioned\nbelow refer to the numbering sequence in the revised manuscript.\nThe contents copied from the revised manuscript are highlighted in yellow.\nReviewers' comments:\nReviewer #3 (Remarks to the Author):\nThe reviewer considers highlighting mechanical properties of LZACO does not confer further novelty\nfor the publication since the incorporation of Al, Cl, and O is quite expectable considering the reported\nviscoelasticity of Li-Al-Cl-O materials (Nat. Energy, 8, 1221 (2023)).\n(Response) We sincerely thank the reviewer for his/her valuable critique. As noted by the reviewer, the\nsuperior mechanical compliance of the Li-Al-Cl-O materials is achieved in the viscoelastic state, rather\nthan the powdery state displayed by most inorganic solid electrolytes. Despite its unique advantage in\nmaintaining intimate electrode-electrolyte contact, the viscoelastic state is not ideal for the pouch-cell\nfabrication techniques that are potentially applicable in the large-scale roll-to-roll manufacturing, as\nthe material in this state would easily overflow under the pressure applied during rolling, making the\nmembrane formation and cell assembly rather difficult (this could be the reason why pouch-cell\nperformance is not reported in the paper noted by the reviewer). In contrast, the powdery solid\nelectrolytes like the sulfide and halide solid electrolytes are more compatible with these procedures\n(Adv. Mater. 35, 2209074, 2023), but they generally display poor mechanical compliance. Therefore,\npreferably superior mechanical compliance should be achieved without inducing the viscoelastic state.\nIncorporating Al, Cl, and O in an inorganic solid electrolyte might be expected to induce the\nviscoelastic state similar to that observed in the Li-Al-Cl-O materials, but the mechanical compliance\nachievable without inducing viscoelasticity remains unknown; in fact, it is also quite possible that, as\nlong as the material does not become viscoelastic but remains powdery, it would only show the kind\nof mechanical compliance displayed by other powdery solid electrolytes. Under this circumstance, the\npresent study not only achieves the mechanical compliance greatly exceeding those of typical powdery\nsolid electrolytes in the non-viscoelastic, powdery state that is suitable for pouch-cell fabrication, but\nalso presents decent pouch-cell data that are absent in the paper noted by the reviewer (Nat. Energy 8,\n1221, 2023). Consequently, we believe the discovery reported here is not easily expectable. We hope\nthis can alleviate the reviewer’s concern about the novelty of the present study.\nFurthermore, the measured Young’s modulus value of LZACO should be explained carefully. As the\nauthors stated “ the mechanical compliance of LZACO cannot possibly surpass the viscoelastic ones,\nsuch as the polymer solid electrolytes….”, generally, Young’s modulus of solid materials will be\ninorganic > polymeric materials. The measured Young’s modulus of LZACO is 1.41, which is even\nlower than many polymers such as PETs, nylons, and etc. Is there any possibility that the measurement\n1\nmethod underestimate Young’s modulus? In this context, it is recommended to measure some\nrepresentative materials including sulfides, halides, and polymers with the same method. If 1.4Li2O-\n0.75ZrCl4-0.25AlCl3 (LZACO) shows the lower Young’s modulus than polymers, the appropriate\nchemical explanation should be discussed in detail.\n(Response) We very much appreciate the reviewer’s insightful suggestion. In the revised manuscript,\nwe measured the Young’s moduli of Li PS Cl (as the representative sulfide solid electrolyte), Li ZrCl\n6 5 2 6\n(as the representative halide solid electrolyte), and a polymer solid electrolyte whose Young’s modulus\nhas been reported before in Nat. Commun. 14, 2301, 2023. It was found that the Young’s moduli we\nmeasured align well with those reported in literature, as shown in Supplementary Fig. 9 (also pasted\nbelow). These data should safely exclude the possibility that the Young’s moduli were underestimated.\nAs for the PETs and nylons mentioned by the reviewer, they are in fact particularly stiff polymers,\nwith Young’s moduli even higher than those of certain inorganic materials. For typical polymer solid\nelectrolytes, their Young’s moduli generally lie below 200 MPa (Joule 6, 2372–2389, 2022; Nature\nCommunications 15, 2500, 2024), which are indeed lower than the 1.41 GPa Young’s modulus\nmeasured for LZACO.\nThe contents above are presented on page 15: “The Young’s moduli of a few such solid electrolytes\nwere measured too, and the results we obtained align well with those reported in literature\n(Supplementary Fig. 9), confirming the reliability of our mechanical characterization.”.\n102\n101\n100\n10-1\n10-2\nSupplementary Fig. 9. Comparison of the Young’s moduli we measured and those reported in literature. PIL\nrepresents a polymer solid electrolyte whose Young’s modulus has been reported before in Nat. Commun. 14,\n2301, 2023; it is prepared via ultraviolet light-initiated copolymerization of 1-allyl-1-methyl-pyrrolidinium\nbis(trifluoromethanesulfonyl) imide ionic liquid, vinyl ethylene carbonate, and polyfluorinated crosslinker\n2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate (OFHDODA) blended with lithium salt (LiTFSI) in the\nmolar ratio of 8:3:2. The reference data for Li PS Cl and Li ZrCl are taken from Joule 8, 1–16, 2024 and Angew.\n6 5 2 6\nChem. Int. Ed. 64 (36), e202510359, 2025, respectively.\n2\n)aPG(\nsuludom\ns’gnuoY\nOur measurement Reported in literature\n17.27 GPa\n15.3 GPa\n8.84 GPa\n7.8 GPa\n31.84 MPa\nLi PS Cl Li ZrCl PIL\n6 5 2 6\nReviewer #4 (Remarks to the Author):\nThe authors have made clear efforts to address the concerns raised in the first review round through\nadditional experiments and analyses. These revisions have strengthened the manuscript; however, the\nwork may not yet fully meet the exceptionally high bar of novelty generally expected for publication in\nNature Communications.\nThe Li–Zr–Cl–O family of solid electrolytes investigated in this study has already been extensively\nreported in the literature, and Al-doping strategies have likewise been previously explored (e.g.,\nEnergy Storage Materials, Vol. 70, June 2024, 103444; Tan et al., Nano Research 17, 8826–8833,\n2024, among others). In addition, the synthesis route employed in the present work—ball milling—\nwhile effective for laboratory-scale preparation, is associated with relatively high production costs,\nhindering scalability and commercial viability. Consequently, it is difficult to regard the proposed\nmaterial as a cost-competitive candidate for large-scale application in solid-state batteries.\n(Response) We are deeply grateful to the reviewer for his/her insightful feedback, which provides us\nwith valuable guidance for improving the present study. In the revised manuscript, we carefully\nanalyzed the processing cost associated with large-scale synthesis as well. Our results suggest that ball\nmilling does often induce unacceptably high processing cost, as the reviewer noted. However, we also\nfound that such cost would decrease considerably with the synthesis time, which is closely related to\nseveral major cost drivers, such as the electricity cost and the instrument depreciation cost; the reason\nwhy ball milling is usually considered costly lies in the fact that most solid electrolytes need to be\nsynthesized through long-duration ball milling (typically 3040 h, sometimes over 80 h).\nFortunately, the ball milling time needed to synthesize LZACO can be significantly reduced, as long\nas the appropriate raw materials are used. If LZACO is synthesized from Li CO instead of Li O, the\n2 3 2\nball milling time needed to reach the same ionic conductivity may be reduced drastically from 30 to 4\nh (Fig. 3ac, also pasted below), which decreases the processing cost from $63.79 L1 to $15.31 L1,\nas shown in Fig. 3d and Supplementary Tables 15 (the basis for such cost estimation is elaborated in\nMethods, and is also pasted below). Given that Li CO is much more affordable than Li O too ($12.64\n2 3 2\nkg1 vs. $210.67 kg1), this raw material replacement reduces the total cost of LZACO from $156.76\nL1 to only $43.70 L1, considerably lower than the $93.50 L1 solid-electrolyte cost for enabling\nreasonable cost of all-solid-state batteries.\nSuch an effective reduction of the synthesis time (and thus the processing cost) may be attributed to\nthe particularly high O content of LZACO. Compared with the purchased Li O, the Li O formed in-\n2 2\nsitu from Li CO decomposition during synthesis would possess much more active reaction centers at\n2 3\nthe surface, thereby giving rise to higher reaction kinetics; similar phenomena have also been observed\nin other compounds (Chem. Soc. Rev. 42, 7571-7637, 2013; Chemistry for Sustainable Development\n22, 345355, 2014; Solid States Ionics 63-65, 3-9, 1993). However, only the O-rich materials can\nbenefit significantly from this effect; if the O content is so low that the synthesis involves only a small\namount of Li O or Li CO , replacing one with the other can hardly make any difference. Fortunately,\n2 2 3\nthe LZACO reported here is a rather O-rich oxychloride; its O/Cl molar ratio (0.37) greatly exceeds\nthose of many Li-Zr-Cl-O solid electrolytes, such as Li ZrCl O (O/Cl = 0.11),\n1.75 4.75 0.5\n2.22 1.11 5.33 0.67 3 0.75 4 2 2 3\nparticularly effective in reducing its synthesis time. The notably high O content that leads to the\naforementioned accelerating effect for synthesis sets LZACO apart from other previously reported Li-\nZr-Cl-O compositions. We hope this can address the reviewer’s concern about the novelty regarding\nthe composition of LZACO, and we sincerely thank the reviewer for helping us identify such an\noriginally neglected advantage of this material.\nThe contents above are presented on page 23: “The total cost (also referred to as “production cost” in\nsome studies62) of a given solid electrolyte may be obtained by summing its raw materials cost and\nprocessing cost. For the LZACO material, both costs can be greatly decreased by replacing Li O with\n2 3 2 3\nthe moisture-sensitive Li O. On the other hand, such raw materials replacement is supposed to suppress\n2\nthe processing cost too, as it can effectively reduce the synthesis time: compared with the purchased\nLi O, the Li O in-situ formed through Li CO decomposition during intense ball milling would contain\n2 2 2 3\na lot more active reaction centers at the surface, thereby enabling faster reaction63. Similar phenomena\nhave also been observed in many other compounds63-65. In particular, given that LZACO is rather O-\nrich, with the O/Cl molar ratio (0.37) greatly exceeding those of many Li-Zr-Cl-O solid electrolytes\nsuch as Li ZrCl O (O/Cl = 0.11)3, Li Zr Cl O (O/Cl = 0.13)44, and Li Zr OCl (O/Cl\n1.75 4.75 0.5 2.22 1.11 5.33 0.67 3 0.75 4\n= 0.25)26, the replacement of Li O would introduce an exceptionally large amount of Li CO in the\n2 2 3\nraw materials, making the aforementioned phenomenon especially effective in reducing the synthesis\ntime. This desirable scenario is verified experimentally. With Li O replaced by Li CO in the raw\n2 2 3\nmaterials for synthesizing LZACO, the Li CO completely decomposes after only 4-h milling, as\n2 3\nindicated by the absence of C signals in the electron energy-loss spectroscopy (EELS) result\n(Supplementary Fig. 13). More importantly, after such raw material replacement, the ball milling time\nneeded to achieve similar degree of amorphization (Fig. 3ab) and ionic conductivity (Fig. 3c) reduces\ndrastically from 30 h to merely 4 h; besides, the Li CO -synthesized LZACO is even slightly more Li-\n2 3\nion conductive than the Li O-synthesized one (2.59 vs. 2.55 mS cm1 at 25 C), despite the much\n2\nshorter synthesis time of the former. Notably, among the four components of the processing cost, i.e.,\ninstrument depreciation, electricity, plant area, and personnel, most are rather sensitive to the synthesis\ntime, as shown in Fig. 3d (detailed estimation procedure in Methods and Supplementary Tables 15).\nSpecifically, the 30-h synthesis time that is rather common among oxychloride solid electrolytes3,47\nwould in fact give rise to a high processing cost of $63.79 L1 for LZACO, even after considering its\nstability in the air with around 4% relative humidity (Supplementary Figs. 1415). Nevertheless, when\nthe synthesis time is reduced to the 4 h achieved above, the processing cost drops to only $15.31 L1\n(Fig. 3d). In the meantime, since Li CO is also much more affordable than Li O ($12.64 kg1 vs.\n2 3 2\n$210.67 kg1, as shown in Fig. 3e and Supplementary Table 6), the raw materials cost also decreases\nsignificantly from $92.97 L1 to $28.39 L1. Taking both costs into account, the replacement of Li O\n2\nwith Li CO decreases the total production cost of LZACO from $156.76 L1 to $43.70 L1 (Fig. 3f\n2 3\nand Supplementary Table 5), which is much lower than the aforementioned $93.50 L1 solid-electrolyte\ncost for enabling reasonable ASSLB cost. Remarkably, this $43.70 L1 cost for LZACO is also much\nlower than that of the prototypic Zr-based (oxy)chloride solid electrolyte, Li ZrCl ; the latter has been\n2 6\ncommonly regarded as a cost-effective solid electrolyte for long due to its competitive raw materials\ncost ($30.71 L1), but, after incorporating the processing cost, its overly long synthesis time of 45 h47\nwas found to result in a rather high processing cost of $109.30 L1 (Fig. 3f and Supplementary Tables\n4\n15), which alone greatly exceeds the $93.50 L1 reasonable cost for solid electrolytes (Fig. 3f). Clearly,\nin order to identify cost-effective, commercially viable solid electrolytes, focusing on the raw materials\ncost alone is not enough; developing solid electrolytes that may be rapidly synthesized to achieve\ndecent processing cost, such as the LZACO reported here, is equally important.”.\nAdditionally, the basis for estimating the processing cost is described on page 43: “To estimate the\nprocessing cost, we assume the solid-electrolyte production to take place in a walk-in enclosure with\n3  20 m2 area and 2.5 m height (Vigor Gas Purification Technologies Co., Ltd.), within which the\nrelative humidity is maintained at 4% and 28 industrial planetary mills (XQM-12T, Changsha\nTianchuang Powder Technology Co., Ltd.) are used to fabricate the solid electrolyte. These industrial\nplanetary mills can produce 28 kg of solid electrolyte per batch. Therefore, dividing the processing\ncost per batch of production by 28 kg and then multiplying the result by the density of the solid\nelectrolyte would yield the processing cost per unit volume of the solid electrolyte. The processing\ncost per batch of production that is needed for this calculation consists of four components: instrument\ndepreciation cost, electricity cost, personnel cost, and plant area cost. The depreciation cost of each\ninstrument was calculated via dividing its price by the depreciation period (acquired from the\nmanufacturer) and multiplying the result by the working time of this instrument during each batch of\nproduction. The electricity cost of each instrument was calculated from the average industrial\nelectricity price for China in September, 2025, the rated power of this instrument, and the time it\noperates at the rated power. For the planetary mill, since it needs to be operated intermittently (such as\n5-min milling followed by 5-min break for cooling), the working time for depreciation cost estimation\nis considered twice the effective milling time for electricity cost estimation. The personnel cost was\ncalculated from the time needed for operating each instrument and the average salaries of battery\nindustry in China reported in January, 202560. The plant area cost was estimated from the time needed\nfor each batch of production, the area of the aforementioned walk-in enclosure, and the industrial\nfacility rent of China, which was obtained by averaging the rents of 30 industrial parks located at\ndifferent cities in September, 2025.”.\n10-3\n4x10-3\n3x10-3\n2x10-3\n10-3\n3 4 5\n10-4\n10 20 30 40 50 60 70 80\n10 20 30 40 50 60 70 80\nFig. 3 | Cost-effectiveness of LZACO. a, b XRD patterns of the LZACO synthesized using Li O (a)\n2\nand that using Li CO (b), respectively, with different planetary mill durations. c Ionic conductivities\n2 3\n5\n).u.a(\nytisnetnI\na\nLZACO synthesized using Li2O\n30-h milled\n10-h milled\n5-h milled\n2q (degree)\n)1-mc\nS(\nC° 52s\nc\nLZACO synthesized using Li2O\nLZACO synthesized using Li2CO3\n)1-mc\nS(\nC°\n52s\nSynthesis time (h)\n).u.a(\nytisnetnI\nb\nLZACO synthesized using Li2CO3 60 45\n5-h milled\n30\n4-h milled\n15\n3-h milled\n0\n4 10 15 20 25 30\n2q (degree)\n)1-L $(\ntsoc\ngnissecorP\n215\n210\n205\n10\n5\n0\nd\nPlant area $63.79 L1\nPersonnel Electricity $54.48 L1 Depreciation $45.15 L1\n$35.83 L1\n$26.50 L1\n$15.31 L1\nLZACO LZACO\nSynthesis time (h) (from Li2O) (from Li2CO3)\n)1-gk\n$(\necirp\ntekram\negareva\n4202\ne\n$210.67 kg1\n$14.04 kg1 $12.64 kg1\n$11.24 kg1\n$0.84 kg1\nLi2O LiCl Li2CO3 ZrCl4 AlCl3\n180\n135\n90\n45\n0\n)1-L\n$(\ntsoc\nES\nf\nProcessing cost $156.76 L1 Raw materials cost $140.01 L1\n$93.50 L-1\n$43.70 L1\nLi2ZrCl6\nat 25 C ( ) of the Li O- and Li CO -synthesized LZACO materials with different lengths of\n25 C 2 2 3\nsynthesis time. Inset: enlarged view of the variation of  for the Li CO -synthesized LZACO.\n25 C 2 3\nd\nProcessing costs of LZACO with different lengths of synthesis time. e Average market prices in 2024\nfor the industrial commodity chemicals involved in the cost estimation. f Solid-electrolyte (SE) costs\nof Li ZrCl , Li O-synthesized LZACO, and Li CO -synthesized LZACO.\n2 6 2 2 3\nSupplementary Table 1. Instrument depreciation costs for producing different solid electrolytes. The Li ZrCl\n2 6\ndensity used for the cost analysis is 2.56 g cm3, as previously reported in Nat. Commun. 12, 4410, 2021, while\nthe LZACO density is measured to be 2.15 g cm3 (details in Methods). “SE” represents “solid electrolyte”.\nLi2ZrCl6 LZACO (from Li2O) LZACO (from Li2CO3)\nAmount of SE produced per batch (kg) 28\nCost per instrument ($) 15169.46\nNo. of instruments involved 28\nPlanetary Depreciation period (year) 7\nmill Effective milling time (h) 45 30 4\nInstrument working time (h) 90 60 8\nDepreciation cost of this instrument ($ L1) 57.02 31.91 4.25\nCost per instrument ($) 164384.56\nNo. of instruments involved 1\nWalk-in\nDepreciation period (year) 15\nenclosure\nInstrument working time (h) 92 62 10\nDepreciation cost of this instrument ($ L1) 10.53 5.96 0.96\nDepreciation cost of all the instruments ($ L1) 67.55 37.87 5.21\nSupplementary Table 2. Electricity costs for producing different solid electrolytes. The Li ZrCl density used\n2 6\nfor the cost analysis is 2.56 g cm3, as previously reported in Nat. Commun. 12, 4410, 2021, while the LZACO\ndensity is measured to be 2.15 g cm3 (details in Methods). “SE” represents “solid electrolyte”.\nLi2ZrCl6 LZACO (from Li2O) LZACO (from Li2CO3)\nAmount of SE produced per batch (kg) 28\nElectricity price ($ kWh1) 0.084\nPower (kW) 3.0\nPlanetary No. of instruments involved 28\nmill Effective milling time (h) 45 30 4\nElectricity cost of this instrument ($ L1) 29.04 16.25 2.17\nNo. of instruments involved 1\nRelative humidity 4%\nPower without people inside (kW) 0.31\nWalk-in\nPower with people inside (kW) 2.51\nenclosure\nTime without people inside (h) 90 60 8\nTime with people inside (h) 2 2 2\nElectricity cost of this instrument ($ L1) 0.25 0.15 0.05\nElectricity cost of all the instruments ($ L1) 29.29 16.40 2.22\n2 6\nfor the cost analysis is 2.56 g cm3, as previously reported in Nat. Commun. 12, 4410, 2021, while the LZACO\ndensity is measured to be 2.15 g cm3 (details in Methods). “SE” represents “solid electrolyte”.\nLi2ZrCl6 LZACO (from Li2O) LZACO (from Li2CO3)\nAmount of SE produced per batch (kg) 28\nLabor cost person ($ h1) 7.04\nNo. of instrument involved 28\nNo. of instrument each person is in charge of 4\nPlanetary\nNo. of people needed 7\nmill\nTime each person needs to spend (h) 2\nPersonnel cost for this instrument ($ L1) 9.01 7.57 7.57\nSupplementary Table 4. Plant area costs for producing different solid electrolytes. The Li ZrCl density used\n2 6\nfor the cost analysis is 2.56 g cm3, as previously reported in Nat. Commun. 12, 4410, 2021, while the LZACO\ndensity is measured to be 2.15 g cm3 (details in Methods). “SE” represents “solid electrolyte”.\nLi2ZrCl6 LZACO (from Li2O) LZACO (from Li2CO3)\nAmount of SE produced per batch (kg) 28\nIndustrial facility rent per month ($ m2) 4.92\nArea of the walk-in enclosure for producing the SEs (m2) 60\nTime needed for each batch of production (h) 92 62 10\nPlant area cost ($ L1) 3.45 1.95 0.31\nSupplementary Table 5. Raw materials cost, processing cost, and production cost for different solid electrolytes.\nThe Li ZrCl density used for the cost analysis is 2.56 g cm3, as previously reported in Nat. Commun. 12, 4410,\n2 6\n2021, while the LZACO density is measured to be 2.15 g cm3 (details in Methods).\nSolid electrolyte Raw materials cost ($ L1) Processing cost ($ L1) Production cost ($ L1)\nLi2ZrCl6 30.71 109.30 140.01\nLZACO (from Li2O) 92.97 63.79 156.76\nLZACO (from Li2CO3) 28.39 15.31 43.70\nThat said, this work offers several notable strengths. The comprehensive crystallinity analysis of the\nhighly amorphous electrolyte, the careful evaluation of its feasibility as a solid electrolyte, and the\ndemonstration of its electrochemical performance in pouch cells using a dry-film electrode\nconfiguration represent meaningful contributions that could serve as useful benchmarks for future\nstudies in the field of solid-state batteries.\nenergy storage or secondary battery technology, rather than Nature Communications.\n(Response) We sincerely thank the reviewer for his/her positive comments on our work, and for his/her\nkind help in strengthening the manuscript. We hope the revisions above can address the reviewer’s\nremaining concerns.\n8"}, {"round": 2, "reviewer_comments": {"reviewer_1": "All my concerns are addressed properly. I now consider that this manuscript is suited to be published.", "reviewer_2": "Dear Authors,\nThank you for your comprehensive and thoughtful responses to the reviewer comments. I have carefully reviewed your\nrevisions and replies, and I am satisfied that all of my concerns have been adequately addressed.\nThe manuscript has been significantly improved in both clarity and content, and I have no further major suggestions. I would\nlike to raise one final, brief point: if feasible, please consider including recent references regarding developments in low-\npressure and current collectors, lithium metal integration, and dry/wet chemistry processes involving the LPSC electrolyte.\nOverall, I believe the revised version meets the standards for publication, and I support its acceptance.\nSincerely, Reviewer", "reviewer_3": "The reviewer considers highlighting mechanical properties of LZACO does not confer further novelty for the publication\nsince the incorporation of Al, Cl, and O is quite expectable considering the reported viscoelasticity of Li-Al-Cl-O materials\n(Nat. Energy, 8, 1221 (2023)).\nFurthermore, the measured Young’s modulus value of LZACO should be explained carefully. As the authors stated “ the\nmechanical compliance of LZACO cannot possibly surpass the viscoelastic ones, such as the polymer solid electrolytes….”,\ngenerally, Young’s modulus of solid materials will be inorganic > polymeric materials. The measured Young’s modulus of\nLZACO is 1.41, which is even lower than many polymers such as PETs, nylons, and etc. Is there any possibility that the\nmeasurement method underestimate Young’s modulus? In this context, it is recommended to measure some representative\nmaterials including sulfides, halides, and polymers with the same method. If 1.4Li2O-0.75ZrCl4-0.25AlCl3 (LZACO) shows\nthe lower Young’s modulus than polymers, the appropriate chemical explanation should be discussed in detail.", "reviewer_4": "The authors have made clear efforts to address the concerns raised in the first review round through additional experiments\nand analyses. These revisions have strengthened the manuscript; however, the work may not yet fully meet the\nexceptionally high bar of novelty generally expected for publication in Nature Communications.\nThe Li–Zr–Cl–O family of solid electrolytes investigated in this study has already been extensively reported in the literature,\nand Al-doping strategies have likewise been previously explored (e.g., Energy Storage Materials, Vol. 70, June 2024,\n103444; Tan et al., Nano Research 17, 8826–8833, 2024, among others). In addition, the synthesis route employed in the\npresent work—ball milling—while effective for laboratory-scale preparation, is associated with relatively high production\ncosts, hindering scalability and commercial viability. Consequently, it is difficult to regard the proposed\nmaterial as a cost-competitive candidate for large-scale application in solid-state batteries.\nThat said, this work offers several notable strengths. The comprehensive crystallinity analysis of the highly amorphous\nelectrolyte, the careful evaluation of its feasibility as a solid electrolyte, and the demonstration of its electrochemical\nperformance in pouch cells using a dry-film electrode configuration represent meaningful contributions that could serve as\nuseful benchmarks for future studies in the field of solid-state batteries.\nTherefore, I would recommend submission to a more specialized journal focused on electrochemical energy storage or\nsecondary battery technology, rather than Nature Communications."}, "author_response": ""}, {"round": 3, "reviewer_comments": {"reviewer_3": "The revised manuscript does not provide new content to justify the claimed novelty, which is in line with the previous Nat.\nEnergy paper.", "reviewer_4": "All my concerns are addressed properly. I now consider that this manuscript is suited to be published."}, "author_response": ""}]

Decision letter