Integrating dry-processing and pre-sodiation enables high-energy sodium ion batteries

Domain: physics
Published: 2025-12-13
Editorial outcome: minor_revision

Abstract
Sacrificial sodium-rich salts pre-sodiation is a safe and promising approach to supplement sodium-ion batteries with additional capacity for energy density enhancement. However, high-cost from additional solvent and low-utilization-ratio caused by loose electrical contact limit its practical application in slurry-coated electrodes. Herein, we demonstrate a dry-processing method to enable complete sodium oxalate decomposition and solvent-free production of thick electrodes. Distinct to particle aggregation in slurry-coated electrodes, a homogenous mixture of Na2C2O4 and conductive agents is generated and wraps Na3V2(PO4)3 particles after high-speed shear-mixing and hot-calendaring of dry-processing method, constructing intimate and durable electronic pathways, thus realizing theoretical decomposition capacity of Na2C2O4 in thick electrodes (54 mg cm-2). This strategy increases the lifespan by 200 cycles and energy density by 82.5% for all-dry-processing sodium-ion batteries with a real capacity of 5.4 mAh cm-2, which highlights the vital role of exploiting mechanical and thermal effects of dry-processing method in sustainable fabrication of high-energy sodium-ion batteries.

Introduction
Sodium-ion batteries (SIBs) are promising candidates to achieve low-cost energy storage due to unlimited sodium source and sustainable electrode materials1–3. However, the widely application of SIBs is still limited due to the relatively low energy density compared to lithium-ion batteries, of which an important and solvable origin is low capacity caused by low initial coulombic efficiency (60–85%) of hard carbon (HC) negative electrode4,5. Pre-sodiation, by sacrificially decomposing sodium-rich compounds to sodium-ions, could effectively address the problem by compensating the irreversible capacity loss of negative electrode and saving sodium inventory of positive electrode6. On the other hand, pre-sodiation is the necessary procedure to solve the sodium deficiency of layered transition metal oxide (TMO) positive electrodes. Compared to O3-type, P2-type TMOs are promising positive electrode materials for SIBs due to their excellent ionic conductivity and cycling stability; while the capacity of the synthesized materials cannot be greater than 2/3 of the maximal value with retaining P2-type structure7. Instead, it is verified pre-sodiation simultaneously replenish the capacity and retain P2 structure by electrochemical reaction8,9. However, new issues arise as using pre-sodiation, i.e., whether the pre-sodiation agents are safe during electrode production, whether the reaction products are non-toxic and easy to remove, and whether the pre-sodiation reaction damage the electrode structure10. Hence, it remains challenging to develop practical pre-sodiation methods that comply with existing manufacturing processes and do not interfere with the original battery performance.

Intensive work has been done to develop novel pre-sodiation materials and methods. Based on the reaction type11, these methods could be generally divided into electrochemical pretreatment12, chemical reaction13 and sacrificial sodium-rich salts14,15. Electrochemical pretreatments need to pre-cycle the negative electrodes in half cell to form stable Solid Electrolyte Interphase (SEI), then disassemble the half-cell to harvest the electrodes, and reassemble the full cell, which is only applicable in laboratory research. Chemical reaction methods can achieve pre-sodiation by direct contact with sodium metal or soaking in sodium-containing organic solution. This method needs the manipulation of metallic sodium and can only be carried out in a glove box, which will inevitably increase production costs and safety issues. As comparison, sacrificial salts were added into the positive electrode during electrode production and in situ decomposed to sodium-ions during charging, which is the cost-effective and safe pre-sodaition method for SIBs16,17.

Various sodium-rich salts have been screened to use as pre-sodiation sacrificial salts, such as inorganic salts of NaN318, NaCrO219, and organic salts of Na2CO320, Na2C2O421, of which the scope is to find non-toxic salts with high capacity and low decomposition potential22. However, the capacity of these salts is generally lower than 400 mAh g–1. Therefore, the main research directions are increasing the capacity utilization ratio and reducing the decomposition potential. The common methods are reducing size to increase reaction surface area23, constructing abundant contact with conductive carbon24, adding catalyst to decrease reaction energy25. As a result, the particle size of the sacrificial reaction agents is generally reduced to lower than 5 μm21,25–27. Considering the mass ratio of sacrificial salts is typically over 10% of positive electrode materials28,29, introducing small-sized salts into the electrode slurry for coating requires a large amount of solvent for dispersion30, which limit the electrode mass loading. Importantly, the organic solvent incurs high electrode production cost: (1) a large amount of energy from removing the solvent during drying the slurry-coated electrode; (2) high capital expense from multiple condensers or distillation towers to recycle the solvent; (3) detailed process and equipment controls to avoid explosion risks from highly flammable solvents. Moreover, the dissolved binder, polyvinylidene difluoride (PVDF), coated on the active material surfaces would increase the cell resistivity, thus reducing device energy and power densities. Also, sacrificial salts are tend to agglomerate in the slurry during drying process, which would form large voids in the PVDF film network by the produced gases during decomposition, which may cause damage of the electrode structure31. The disconnect with conductive carbon network cuts down the electronic pathways, hindering the fully decomposition of sacrificial salts. As elucidated in Fig. 1a, pre-sodiation using sacrificial salts may not be compatible with slurry-coating electrodes, yet to be taken seriously and addressed.

Dry-processing electrode is an effective way to solve all the issues in slurry-coating electrodes, as shown in Fig. 1b. Dry-processing electrodes are made by dry-mixed powder at high speed (typically over 18,000 rpm) to make binder fibrillation, and then undergoing multiple hot rolling (100~200°C) to obtain the required thickness and compacted density, and finally hot-calendared with current collector under low pressure to obtain electrode products32–34. Benefit from higher mechanical strength of polytetrafluoroethylene (PTFE) fiber network compare to PVDF, dry-processing method produces electrodes with high thicknesses for high mass loading and large compacted density for close connection with the conductive agents35, which may facilitate complete sacrificial salts decomposition. In contrast, the electrode tap density of slurry-coating electrodes is low because the pressure used in the final roll-press is limited to prevent wrinkles in the current collectors, which in turn results in high resistance, low energy density, and poor cycle life. Importantly, as integrating with pre-sodiation, the voids generated by decomposition of sacrificial salts could adjust the porosity of dry-processing electrodes, which may accelerate the ion diffusion process29,36. Therefore, synergistic use dry-processing method and sacrificial salts pre-sodiation is expected to enable sustainable, high-capacity electrode production for high-energy-density and low-cost SIBs.

Results
Production of dense pre-sodiation positive electrodes with high loading mechanical adhesion.

To overcome the intrinsic poor electronic conductivity of Na2C2O4, the commercial Na2C2O4 powder was ball-milled to reduce the particle size for enhanced contact with conductive agents. The morphology of ball-milled Na2C2O4 is obtained using scanning electron microscope (SEM) in Fig. 2a, b, which shows polyhedron with reduced particle sizes of ~2 μm. The electrochemical performance of ball-milled Na2C2O4 was further investigated using slurry-coating electrodes with Super P conductive carbon, where the mass ratio of Na2C2O4, Super P and PVDF was 70:20:10. Using large amount of N-methyl-2-pyrrolidone (NMP) solvent for dispersion, Na2C2O4 particles are evenly distributed in conductive carbon (Fig. 2c), contributing to efficient electron conductive network. Supplementary Fig. 1 shows the charge and discharge curves of ball-milled Na2C2O4 electrode in a potential range of 2.5–4.5 V vs Na/Na+ under current density of 0.2 C (1 C = 400 mA g–1). The electrode exhibits initial charge capacity of 365.23 mAh g–1 with seldom no capacity in the subsequent cycles, proving the feasibility as a sacrificial agent for supplementary sodiation. However, the decomposition capacity is lower than the theoretical capacity of Na2C2O4 (400 mAh g–1) and the decomposition potential is high with value of ~4.3 V vs Na/Na+. The morphology of the electrode after cycling was tested to figure out the reason, where abundant voids (yellow circle) and residual Na2C2O4 particles (red circle) are observed in Fig. 2d. The residual Na2C2O4 particles are aggregated together without contact with the conductive agents, indicating the loose and fragile mechanic and electronic network of slurry-coating electrode hindering the full decomposition. The issue would be more announced when part of the Na2C2O4 is decomposed to gas, which would take away part of the conductive agents and cause structural damage31. Therefore, developing electrode structure with strong mechanic and electronic networks is crucial for cathodic pre-sodiation using sacrificial salts containing gas products, among which dry-processing electrodes are promising.

The effect of ball-milled Na2C2O4 powder on electrode production was evaluated by fabricating two types of electrodes with Na3V2(PO4)3 (NVP) as active material: conventional slurry-coating (SC) electrodes and dry-processing (DP) electrodes. Low solid content of 40% was applied in SC electrodes by adding NMP to prepare homogenous slurry with well fluidity for coating, which would further need more time for solvent-evaporating step. As shown in Supplementary Fig. 2a, a bumpy surface of SC electrode after coating process was observed, which might due to the alkaline Na2C2O4 triggers PVDF gelation37. Moreover, SC electrodes failed to provide sufficient mechanical adhesion for producing high-mass-loading electrodes, which was easy peeled off and powder shedding as the thickness reach ~230 μm shown in Supplementary Fig. 3. As comparison, DP electrodes are produced without using solvent and able to produce electrodes without thickness limitation. We fabricated DP electrodes by dry-mixed all the powders in commercial blender at high speed, where the coupled shear force and thermal effect ensured fibrillation of PTFE and uniform dispersion of powders. Supplementary Fig. 2b shows optical image of the free-standing DP film, which exhibits flat surface. The distinction is more convinced in the height distribution on the electrodes, which was obtained using optical microscopy in Fig. 2e–i. Compare to drastic contour height variation with maximum height difference of ~160 μm for SC electrodes, homogenous contour height was observed on DP electrodes, which only shows maximum height difference of ~35 μm. In summary, DP method realizes fabrication of thick, homogenous and smooth electrode containing Na2C2O4 powder, which is free of using solvent and avoids solvent evaporating and recycle step, demonstrating processability for large-scale and sustainable pre-sodiation electrode production.

Furthermore, it is worthwhile to compare the electrode structures to illustrate the difference in the effects of the SC and DP methods on mechanical adhesion. The SC and DP electrodes were cut and milling using Ar+ to obtain intrinsic cross-sectional structure38, as shown in Fig. 2j, l, and Supplementary Figs. 4 and 5. In SC electrodes, loose contact between NVP particles with abundant pores are observed, where the PVDF binder only connects the adjacent active material particles through point-to-point adhesion (as illustrated in Fig. 2k). As comparison, benefiting from the long fiber skeleton formed by PTFE, the NVP particles in DP electrodes shows significantly improved contact with the conductive agents (darker contrast in Fig. 2l). As illustrated in Fig. 2m, The Na2C2O4 powders are closely dispersed in the gaps where the conductive agents are located, contributing to durable and unimpeded electronic pathways. As a result, the thickness of SC electrodes was limited to ~80 μm, of which the mass loading was 11 mg cm–2. DP electrodes can achieve continue production with thickness of ~400 μm and length of ~30 cm (Supplementary Fig. 2b, Supplementary Videos 1 and 2), corresponding to high mass loading of ~54 mg cm–2. According to the calculations in Supplementary Tables 1 and 2, the compacted densities of SC and DP electrodes were 1.17 and 1.61 g cm–3, respectively, corresponding to porosities of 60.06% and 45.91%. The massive production of DP electrodes containing Na2C2O4 in the same electrode formula was verified using commercial and low-cost Na[Ni1/3Fe1/3Mn1/3]O2, where the dry-mixed powder, the roll-to-roll hot-calendaring process and winded DP electrodes are shown in Fig. 2n–p and Supplementary videos, respectively. Consequently, we achieve production of dense pre-sodiation positive electrodes with high loading using DP method, thereby establishing intimate electrical contact between NVP, conductive agents and Na2C2O4 powders.

Function Mechanisms of the DP electrodes on Na2C2O4 decomposition

The chemical compositions of electrodes were characterized to ramification of different electrode structure on the decomposition of Na2C2O4. Differential electrochemical mass spectrometry (DEMS) was conducted to monitor the evolution of carbon dioxide (CO2) for elucidating the accurate pathway, as the decomposition of Na2C2O4 only produces CO221,39. Figure 3a shows the correlation between electrode potential and dynamic gas evolution rate. Potential plateaus, ascribed to the decomposition of Na2C2O4, were observed in the potential curves of both SC and DP electrodes, which were started from 4.27 and 4.11 V and were accompanied by the production of CO2. According to the increase point of gas production rate, we found the actual decomposition of Na2C2O4 in DP electrodes begins at 3.51 V, while the onset potential was higher at 3.69 V in the SC electrode, clarifying that dense DP electrodes reduce the reaction overpotential of Na2C2O4 decomposition. Moreover, DP electrode shows larger plateau capacity accompanied by a longer CO2 production period compared to SC electrode, implying a greater proportion of the Na2C2O4 has decomposed in DP electrodes, which were further verified using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests. Figure 3b depicts the XRD patterns of SC and DP electrodes after charging to different potentials, which are as prepared, to 3.8 and to 4.5 V. The (410) diffraction peak of Na2C2O4 is chosen to clearly show the residual phases without interference by the signal from NVP, which locates at 2θ = 38.541° and highlighted using orange star. Compared with persistent (410) peak in SC electrodes, the (410) diffraction peak of Na2C2O4 in DP electrodes decreases in intensity as charged to 3.8 V and vanish entirely as charged to 4.5 V, which verifies the complete consumption of Na2C2O4 in DP electrodes. XPS spectra in Fig. 3c, d further corroborate the evolution process observed in the XRD patterns. In C 1s and O 1s spectra, the intensity of C=O bond (289 eV, 531.7 eV) in SC electrodes slightly decreased and maintained a high intensity as charged to 4.5 V, indicating that there was residual Na2C2O4 in the SC electrodes. In contrast, C=O signal vanishes in C 1s spectra and largely reduced in O 1s spectra for DP electrodes charged to 4.5 V, again confirming the completely decomposition of Na2C2O4 in DP electrodes. The intensities of characteristic peaks ascribed to Na2C2O4 decreased as charging to 3.8 V for both SC and DP electrodes, which is inconsistent with that the decomposition of Na2C2O4 starts before 3.8 V in Fig. 3a. In short, complete Na2C2O4 decomposition is achieved in dense DP electrodes, other than in loose SC electrodes, which shows a reduced reaction overpotential and a larger capacity.

To further explore the function mechanism of electrode fabrication method on Na2C2O4 decomposition, electrode structure after pre-sodiation process was comprehensive investigated. Figure 4a, b shows the surface morphology and the corresponding energy-dispersive X-ray spectroscopy mapping images of SC electrode as charged to 4.5 V. From pronounced Na and O signal, severe aggregation of Na2C2O4 particles is observed in the pores between NVP particles. The Na2C2O4 aggregates are separated from the conductive carbon and exhibit an inconsistent distribution with the C signal, indicating that the incomplete decomposition is caused by disconnection of the electronic conductive pathway. Similarly, the remnants of Na2C2O4 clusters are observed in the cross-section of the SC electrode as charged to 4.5 V, which are highlighted in Fig. 4c, d. The dispersion limitations in slurry casting (SC) arise from two sequential effects: slurry-dispersion challenge and drying-induced redistribution. High surface area of Na2C2O4 particles necessitates excess solvent (NMP) to stabilize the dispersion- yet during drying, solvent evaporation generates capillary forces that cause crack formation and material inhomogeneity40,41. Supplementary Fig. 6a, b shows sectional morphology of slurry-coated electrodes after solvent drying, which provides evidence supporting the uneven and separated distribution between Na2C2O4 and conductive agents. Even under elevated calendaring pressure of ~50 MPa, aggregated Na2C2O4 domains persist, which fracture into isolated fragments, losing electrical contact with conductive networks (red arrows in Supplementary Fig. 6h, l).

In contrast, no Na2C2O4 particles are observed on surface of DP electrodes as charged to 4.5 V, which is verified by the consistent distribution of Na, V, and P signals in Supplementary Fig. 7. The sectional structure was compared to figure out Na2C2O4 distribution inside the DP electrodes. As shown in Fig. 4e, dense electrode structure with two kinds of contrast is observed in the section of DP electrodes. According to V and C distribution in Fig. 4f, the light and dark phases are NVP and conductive carbon, respectively. Importantly, there is no polyhedron-shaped Na2C2O4 particle, while obvious Na signals are observed distributed in the gap between NVP particles. This Na signal is highly consistent with the C signal, indicating that DP method produces a homogeneous mixture consisting of conductive carbon and Na2C2O4, thus establishing an intimate and permanent electrical contact. Hence, complete Na2C2O4 decomposition is achieved as DP electrodes charging to 4.5 V, showing that the Na signal comes only from the NVP particles, which is the same distribution with the V, O, and P signal (Fig. 4g, h and Supplementary Fig. 8).

The physical properties of Na2C2O4 were tested to explain the change in Na2C2O4 morphology. Differential scanning calorimetry (DSC) curve (Fig. 4i) shows no obvious endothermic peak as heating to the 300°C, indicating the Na2C2O4 remained solid during fabrication of DP electrodes21, which is verified by the fact that Na2C2O4 remained solid during the melting point test (Fig. 4k). Further, the Young’s modulus of Na2C2O4 were tested using atomic force microscopy (AFM), showing a sharp drop in value at high temperatures in Fig. 4j, k and Supplementary Table 3. Specifically, Young’s modulus decreased to 71.3 and 30.3 MPa as the temperature is 100 and 150°C, while it exhibits a high value of 609.7 MPa at 25°C. Optical and SEM images of the material powder before and after dry-processing were compared in Supplementary Figs. 10 and 11, in order to illustrate the enhanced Na2C2O4 dispersion in electrodes by salt deformability. The mixed powder appears uniformly gray, indicating that the Na2C2O4 and electrode materials are mixed evenly. After high-speed dry-mixing, Na2C2O4 particles exhibit rougher surface and decreased particle size (from ~2 μm to ~1 μm) than original state, confirming deformation. Different from Na2C2O4 aggregation inside slurry-coated electrodes in Supplementary Fig. 6, the bright white Na2C2O4 particles are evenly distributed on the surface of NVP particles. Moreover, the deformed Na2C2O4 particles were also inserted into the interior of the aggregated VGCF, which improves the dispersity of Na2C2O4 in VGCF. Importantly, the high roller pressure and heat during hot-calendaring at 120°C further promote Na2C2O4 deformation and compress the mixture to form interlocked structure of VGCF and Na2C2O4, which appeared as a mixture of C–Na element distribution without the observed polygonal morphology of Na2C2O4 (Fig. 4e). This indicates that the mechanical and thermal effects of DP method play critical roles in intimate dispersing sacrificial salts, which deform the particles by shear force and the accompanying heat during high-speed dry-mixing process as well as compress the mixture during hot-calendaring process42.

Electrochemical properties of pre-sodiation positive electrode

Having clarified the function mechanisms of DP electrodes on Na2C2O4 decomposition, the electrochemical performance of pre-sodiation positive electrodes was further evaluated using half-cell. Figure 5a shows the initial two potential curves of SC and DP electrodes, which in initial cycle were charged to 4.5 V under 0.2 C, and in second cycle were charged to 3.8 V under 0.1 C. The decomposition of Na2C2O4 was observed as a plateau in initial cycle of both electrodes, of which distinct characteristics could be found. The decomposition of Na2C2O4 in SC electrodes shows noticeable high potential plateau at 4.36 V with limited capacity of 29.76 mAh g–1 based on the mass of NVP. The decreased electrode mass corresponds to a low decomposition capacity of 249.1 mAh g–1 based on the mass of Na2C2O4 (Supplementary Table 4), which is significantly short of theoretical value of 400 mAh g–1. Same incomplete Na2C2O4 decomposition was observed in SC electrodes calendared under 50 MPa, which show limited decomposition capacity of 250.1 mAh g–1, as shown in Supplementary Fig. 12. The results indicate the Na2C2O4 decomposition in SC electrodes is incomplete and has sluggish kinetics with large overpotential, attributing to the Na2C2O4 aggregation and fragile electrical contact. In contrast, DP electrodes significantly reduce the plateau potential of Na2C2O4 to 4.16 V. Importantly, the decomposition of Na2C2O4 maintains a relatively stable potential, showing a flat plateau in the range of 4.16–4.23 V, indicating improved reaction kinetics with low overpotential. The decreased electrode mass corresponds to a capacity of 399.8 mAh g–1, which is equivalent to the capacity of the complete decomposition of Na2C2O4 (Supplementary Fig. 13 and Supplementary Table 5). The performance of DP electrodes containing 20 wt% Na2C2O4 was further evaluated by analyzing decomposition capacity, electrode mass change and elemental distribution in Supplementary Figs. 14–16. Specifically, DP electrodes with 20 wt% Na2C2O4 maintain effective pre-sodiation with a decomposition capacity of 394.28 mAh g–1 based on the mass of Na2C2O4 (Supplementary Table 6). A comparative analysis of various pre-sodiation/lithiation positive electrode using sacrificial additives is presented in Fig. 5b and Supplementary Table 7, highlighting the advantages of our pre-sodiation positive electrode fabricated by DP method in both decomposition capacity and positive electrode mass loading for practical sodium supplementation.

The rate performances of electrodes with and without pre-sodiation were evaluated and shown in Fig. 5c and Supplementary Figs. 17–19, which were charged to 4.5 V and 3.8 V in the initial cycle, respectively. DP electrode with pre-sodiation shows higher capacities of 100.9, 82.55, 48.17 and 105.98 mAh g–1 under current densities of 0.3, 0.5, 1.0 and back to 0.3 C than DP electrodes without pre-sodiation, which are 93.65, 67.17, 39.73 and 93.86 mAh g–1. As comparison, slightly reduced capacity value of ~1.47 mAh g–1 with severe increased voltage overpotential of ~0.0301 V are observed in SC electrode with pre-sodiation compare to SC electrode without pre-sodiation. These results indicate Na2C2O4 decomposition can improve reaction kinetics in DP electrodes, but deteriorate the performance of SC electrodes, which are further investigated by resistance analyzes.

The electrochemical impedance spectroscopy (EIS) was tested using symmetric cells with two identical electrodes, which obtains the intrinsic resistances from the tested electrodes without the interference from sodium metal as testing in half-cells43. The EIS profile of DP and SC electrodes are shown in Fig. 5d, e and fitted using the equivalent circuit model (summarized in Supplementary Tables 8–11), which composed of ohmic resistance (Rohm), charge transfer resistance (RCT) and diffusion resistance (W). For comparison between SC and DP electrodes, the higher absolute impedance in DP electrodes versus SC counterparts is primarily attributable to differences in electrode thickness. Specifically, the DP electrode’s 5 times greater thickness inherently elevates its absolute impedance, even assuming identical intrinsic conductivity. Hence, absolute impedance comparisons across different electrode constructing method are less meaningful, and the resistance is compared between electrodes manufactured by the same procedure. For both SC and DP electrodes, Rohm increases by ~2 Ohm after pre-sodiation, which may due to the accumulation of side-reaction products of electrolytes during charging to 4.5 V. Larger RCT is also observed in SC electrodes after pre-sodiantion than SC electrodes without pre-sodiantion, causing larger internal polarization. In contrast, DP electrodes after pre-sodiantion show a reduced RCT from 118.1 to 107.1 Ohm of DP electrodes without pre-sodiation, which proves the fast kinetics obtained by Na2C2O4 decomposition, contributing to larger capacities under high current densities. The different results are caused by fact that Na2C2O4 was completely removed from the DP electrode and generates pores for enhanced electrolytes infiltration, while a certain amount of non-conductive Na2C2O4 remained in the SC electrode to hinder the electron transfer, as observed in Fig. 4a–d. The resistance relationship is consistent with the overpotentials of potential profiles in rate tests (Supplementary Figs. 17 and 18), where DP electrodes after pre-sodiation show lower overpotential than that of DP electrodes without pre-sodiantion, but SC electrodes after pre-sodiation show higher overpotential. The degrees of Na2C2O4 decomposition were further verified by weighing the electrode before and after charging to 4.5 V. As shown in Supplementary Tables 4 and 5, the decreased mass was 62% of the Na2C2O4 added into SC electrode. In contrast, the decreased mass was equal to 99.82% of the Na2C2O4 added into DP electrode, again proving the complete Na2C2O4 decomposition by DP method. The consistency with chemical characterization, morphology observation and electrochemical performance verifies the synergistic effect of DP method and sacrificial salts pre-sodiation for high sodium utilization ratio and improved electrode performance.

To illustrate the influence of additional pores generated by Na2C2O4, the ion diffusion properties were investigated. The compacted densities and porosities of SC and DP electrode after pre-sodiation are compared in Supplementary Fig. 20 and Supplementary Tables 12 and 13. Tiny effects of generated pores are found for SC electrodes with compacted densities decreased by 0.06 g cm–3 and porosity increased by 2.91%, due to the incomplete Na2C2O4 decomposition and porous nature of original SC electrode. In contrast, DP electrodes show a significant reduced compacted densities from 1.61 to 1.41 g cm–3, of which the porosity increased from 45.91% to 53.84%, showing the feasibility of sacrificial salts pre-sodiation on structural adjustment. The ionic resistances (Rion) were calculated and summarized in Fig. 5f44. Specifically, Rion of DP electrodes decreased from 437 to 372.2 Ohm after pre-sodiation, while similar Rion of SC electrodes were observed before and after pre-sodiation. Galvanostatic intermittent titration technique (GITT) results also support improved ion-diffusion properties of DP electrodes (Fig. 5g, h), where DP electrode after pre-sodiation exhibits much lower ion diffusion barriers and IR-Drops compare to DP electrode without pre-sodiation45. Hence, it is verified that the decomposition of Na2C2O4 effectively increase the porosity of the dense DP electrodes, thereby enhancing electrolytes infiltration and accelerating ion migration, further contributing to the reduced diffusion resistance and larger capacities.

Effect of sacrificial Na2C2O4 pre-sodiation on DP positive electrode

To evaluate the impact of pores on electrode structure, the morphology of surface and section of DP electrodes were characterized using SEM. The surfaces of DP electrodes before and after Na2C2O4 sacrificial decomposition are compared in Supplementary Fig. 21, which were separated by color segmentation and phase quantification based on contrast to vividly analyze the porosity of surface. The porosity of surface increased from 0.92% to 1.32%, contributing to better penetration of electrolyte into the DP electrodes, which also implies more volume inside the electrode is occupied by pores. Consequently, DP electrodes show increase in thickness from ~410 μm to ~425 μm after pre-sodiation process (Fig. 6a, b and Supplementary Figs. 22 and 23). Importantly, DP electrodes maintained intact and smooth structure without the detachment of active materials, demonstrating that strong mechanical skeleton formed by PTFE fibers is able to withstand internal pressure of the gas generated during pre-sodiation. Detailly, Fig. 6c, d shows that the pore size in DP electrodes was grown from ~250 nm to 1.5 μm after pre-sodiation process, resulting in an increase in the cross-sectional porosity from 6.5% to 9% (Fig. 6e–h and Supplementary Fig. 24), which were confirmed by more positions of sectional structure in Supplementary Figs. 25 and 26. These enlarged pores connected together to build an unobstructed electrolyte migration way along the thickness direction of DP electrodes, as illustrated in Fig. 6i.

A 2D modeling was conducted to gain insights of the advantages of increased porosity on electrolyte infiltration and ion diffusion. The geometry was re-constructed based on the sectional images in Fig. 6c, d46, which extracted the differences in the structure and number of pores. The variation of electrolyte concentration in the pores during discharging at 0.1 C are shown in Fig. 6j, k and Supplementary Videos 3, 4, of which the initial states of both electrodes were set as 1 mol L–1. During discharging, sodium-ions are stored in the NVP particles, consumed in the electrolyte and replenished from separator, resulting in different electrolyte concentrations along the thickness direction. Benefiting from enlarged pore structure, DP electrode with pre-sodiation shows a lighter blue distribution near the current collector and also darker red distribution near separator compare to DP electrode without pre-sodiation. As summarized in Fig. 6n, DP electrode with pre-sodiation maintains average electrolyte concentration of 0.94 mol L–1 at the end of discharge (30,000 s), which is 59% higher than that of DP electrode without pre-sodiation. Consequently, DP electrode with pre-sodiation shows more amount of fully sodiated NVP particles after same discharge time in Fig. 6l, m, which achieves 5.8% higher average sodium concentration in NVP particles than that of DP electrodes without pre-sodiation at the end of discharge (Supplementary Fig. 27e). Under higher current density of 0.5 C (Supplementary Fig. 28), electrolyte concentration gradients between electrode sides intensify for DP electrodes without pre-sodiation; while DP electrode after pre-sodiation maintain high average electrolyte concentration of ~0.90 mol L–1, which shows red distribution throughout electrode thickness. The 2D modeling results verify that the enlarged pores reduce the electrolyte concentration polarization, supporting the enhanced ion diffusion kinetics and rate capabilities of DP electrodes achieved by pre-sodiation process.

Performance of all-DP SIBs with sodium replenishment

The application of DP pre-sodiation positive electrode using Na2C2O4 was demonstrated using coin-cell setup SIB full-cell of HC||NVP as testing vehicle. HC electrodes were made by DP method to realize high areal capacity with a mass loading of 23.31 mg cm–2. As shown in Supplementary Fig. 29, DP HC electrodes show an areal capacity of 6.58 mAh cm–2, of which the reversible discharge capacity ratio of anode to cathode is ~1.2:1. Figure 7a and Supplementary Fig. 30 illustrate the successive decomposition of Na2C2O4 in SIB, exhibiting a fluctuating curve in 3.8–4.1 V and flat plateau in 4.1–4.25 V, which is in consistency to the gas evolution and electrochemical properties from DEMS and half-cell tests. SIB without pre-sodiation exhibits low discharge capacity of 63.51 mAh g–1 with a low initial coulombic efficiency of 59.2%, indicating large irreversible capacity, which is consumed by the formation of SEI on HC electrode and side-reaction of PTFE with sodium-ions in negative electrode47. Pre-sodiation compensates the large irreversible capacity of DP HC electrodes (the compensated capacity is summarized in Supplementary Table 14), which enables SIB to deliver higher reversible capacity of 100.42 mAh g–1 along with a high areal capacity of 5.4 mAh cm–2. As shown in Fig. 7b, c, SIB with pre-sodiation achieves consequently high rate capabilities with capacities of 101.52, 83.92, 59.12 and 81.99 mAh g–1 under current densities of 0.1, 0.3, 0.5 C and back to 0.3 C. The corresponding voltage curves under various current densities are compared in Fig. 7c, where SIB with pre-sodiation show both enlarged capacity and voltage interval without behavior of sodium plating, ensuring the safety of SIB. This promotes the enhancement of both energy density and power density of SIBs (Fig. 7d and Supplementary Table 15), which are 191.4 Wh L–1 @ 68.36 W L–1 under 1.58 mA cm–2, corresponding to 82.5% increasement of volumetric energy density under similar condition for SIB without pre-sodiation. Moreover, as shown in Fig. 7e and Supplementary Fig. 31, SIB with pre-sodiation obtains stable cycling with a retained capacity of 76.03 mAh g–1 under 0.2 C after 100 cycles, while SIB without pre-sodiation shows fast capacity decay to 53.32 mAh g–1 after 100 cycles. Detailed voltage curves of SIBs upon cycling are depicted in Fig. 7f, g, which show a noticeable stability and increase in average voltage for SIB with pre-sodiation, contributing to higher specific energy of 203.8 Wh kg–1 (based on active material mass of positive and negative electrode) with a slower decline rate. More importantly, the specific capacity of SIB with pre-sodiation remained at 61.95 mAh g–1 after 200 cycles, still higher than the capacity of 61.88 mAh g–1 in 4th cycle for SIB without pre-sodiation. These results highlight the enhancement of both cycle lifespan and energy density by using the DP pre-sodaition positive electrode. The improved interfacial passivation and stability by pre-sodiation were further investigated by analyzing the composition and structure of SEI on HC electrodes (Supplementary Figs. 32–34). Depth-resolved XPS and TEM collectively indicate that a Na2CO3-rich SEI was formed under influence of Na2C2O4 decomposition, which are closely arranged at the boundary of HC, contributing to a dense and complete protective layer for enhanced interfacial stability. By contrast, SEI formed without pre-sodiation treatment is organic-rich and does not completely cover the HC boundary. Moreover, high-temperature cycling test (40°C) were tested to verify the interfacial stability in Supplementary Fig. 35, where SIB with pre-sodiation retained 80.3% and 77.2% capacity after 30 cycles under current densities of 0.1 C and 0.2 C, respectively. Comparing to the state-of-the-art SIBs with sodium replenishment in Fig. 7h and Supplementary Table 12, the DP produced pre-sodiation positive electrode in our work enables all-DP SIB to achieve competitive overall performances, especially in aspects of largest capacity after longest cycling under highest current densities with the highest sustainability and low cost.

Methods
Electrode preparation
Na3V2(PO4)3 (NVP), hard carbon (HC), Super P, vapor-grown carbon fiber (VGCF), PVDF, PTFE were purchased from Shenzhen Kejing Materials Technology Co., Ltd, China. Sodium metal counter electrode (450 μm thickness and 15.6 mm diameter) was purchased from Canrd Technology. Celgard 2500 and Glass fiber (GF/A, Whatman) were purchased from Canrd Technology. Electrolytes with formula of 1 M NaPF6 in diglyme and 1 M NaClO4 in EC:DEC (1:1 in vol%) with 5% FEC were purchased from DoDoChem, Ins., China, which were used without further treatment. Sodium oxalate (Na2C2O4) was purchased from Sinopharm chemical reagent Co., Ltd, China, which was ball-milled with ethanol as solvent for 4 h at a rotating speed of 500 r min–1 to reduce the particle size.

Na2C2O4 electrodes were slurry-coated on Al foil, of which the mass ratio of Na2C2O4, Super P and PVDF was 70:20:10. Pre-sodiation positive electrodes were made by slurry-coating and dry-processing methods. For slurry-coated positive electrode, slurry composed of NVP, VGCF, Super P, PVDF and Na2C2O4 in a mass ratio of 90:1:3:6:9 was mixed using NMP and coated on Al foil, of which the solid content was around 40%. The electrodes were dried at 80°C in vacuum for 8 h to remove the NMP. After drying, the electrodes were calendared under pressure of ~10 MPa, of which the thickness was decreased from 120 to 80 μm. The mass loading of slurry-coated electrodes is ~11 mg cm–2. For dry-processing electrode, NVP, VGCF, PTFE and Na2C2O4 were dry-mixed in a mass ratio of 90:4:6:10 using commercial blender, which were mixed in high speed of 18,000 rpm. Then, the uniform powder was hot-calendared under 120°C to form self-supported film with thickness of ~400 μm, of which the mass loading is ~54 mg cm–2. Dry-processing HC electrodes were fabricated by same procedure, of which the mass ratio of HC, VGCF and PTFE was 95:3:2. The dry-processing HC electrodes were hot-calendared to thickness of ~300 μm, of which the mass loading is ~23 mg cm–2. The positive and negative electrode were punched into disks with diameters of 12 mm and 13 mm for coin cells, respectively. All electrodes were dried at 80°C in vacuum overnight before use. The separator was punched into disks with diameters of 19 mm, which were dried at 60°C in vacuum overnight before use.

Electrochemical measurements
All cells were assembled in Ar-filled glove box with water and oxygen content below 0.1 ppm. Half cells were fabricated using 450 μm sodium metal foil as counter electrode, 1 M NaPF6 in diglyme as electrolytes, and Glass fiber as separator. 100 μL electrolyte was added in half cells to standardize. The ether-based electrolyte is used for reduce the ohmic polarization of sodium metal counter electrode to obtain capacity properties of both positive and negative electrode; while the significant overpotential of sodium metal in ester electrolyte leads to undetected capacity of HC below 0.1 V vs Na/Na+5. Full cells were fabricated using dry-processing NVP as positive electrode and dry-processing HC electrodes as negative electrode, 1 M NaClO4 in EC:DEC (1:1 in vol%) with 5% FEC as electrolytes, and Celgard 2500 as separator. 80 μL electrolyte was added in HC||NVP full cells to standardize. Symmetric cells were fabricated using two same electrodes with Glass fiber as separator, which were used to obtain actual resistance without interference from sodium metal electrodes in half cell. 50 μL electrolyte was added in symmetric cells to standardize. The galvanostatic charge and discharge tests were conducted using Neware battery test system (CT-4008T-5V50mA-164, Shenzhen, China) at room temperature (25°C). All the electrochemical experiments have been tested three times for reproductivity, and the data reported in the graphs refers to a single cell. Specific capacity was calculated based on the active materials. For the GITT measurements, the ten data points were acquired per second. The volumetric energy densities and power densities during rate tests were calculated based on thickness and area of positive electrode (410 and 425 μm), negative electrode (300 μm), separator (16 μm) and current collectors (2 × 18 μm). The gravimetric energy densities during cycling tests were calculated based on active mass of positive and negative electrode. EIS measurements were performed on BioLogic VMP3 system at room temperature (25°C), which were conducted using symmetric cell at the open circuit voltage within the frequency of 10–2–106 Hz. The amplitude of potentiostatic perturbation during EIS tests was 10 mV.

Characterization
The cycled coin cells were disassembled in Ar-filled glove box for the preparation of electrode samples. The NVP and HC electrodes were sealed in Ar-filled bag before characterization. SEM and EDX was conducted using Zeiss Sigma 300. Height distribution was measured using optical microscope (KEYENCE, VR-5000). XPS was conducted using Thermo Scientific K-Alpha+. During in-depth XPS test of HC electrodes, the electrodes were etched using Ar-ions. The etching rate was 0.2 nm s–1 (corresponds to the standard Ta2O5 samples). Raman spectroscopy was conducted using Horiba LabRAM HR Evolution, of which the spot size was 1 μm. XRD measurements were carried out on a Bruker D8 Advance diffractometer equipped with a Cu Kα radiation (λ = 1.54 Å). DEMS was conducted using mass spectrometer (QAS100, Linglu Instruments). DSC of Na2C2O4 was tested using Netzsch STA 449 F3 under heating rate of 5°C min–1 in temperature interval of 30–300°C. Molten point tests of Na2C2O4 were conducted using Buchi M-560 melting point system under heating rate of 10°C min–1 to 250°C. Young’s modulus of Na2C2O4 were calculated from force curves under different temperatures tested using AFM, which were conducted using Bruker Dimension XR under temperatures of 25, 50, 100, 150, 200 and 250°C. Transmission Electron Microscope (TEM) characterizations of SEI were obtained using field-emission transmission electron microscope (TEM, Talos F200X, 200 kV, Thermo Scientific, US).

Modeling
The geometry was re-constructed based on the sectional SEM images, which was figured, meshed and simulated using COMSOL Multiphysics 6.2. The electrochemical model equations were derived based on lithium-ion batteries35,48,49. The electrochemical model parameters were set based on literature50–52. The equilibrium potentials of dry-processing NVP electrodes were fitted from Supplementary Fig. 17. It was assumed that the electrolyte concentration was uniformly distributed in the entire geometry and the state of sodiation of NVP particles was 10% in initial state.

Data availability
Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This paper aims to enhance the energy density of sodium-ion batteries by simultaneously introducing a dry electrode fabrication process and a pre-sodiation strategy using a sacrificial salt, enabling the development of high mass-loading electrodes. However, the study primarily focuses on energy density improvement by applying previously established concepts, without providing sufficient scientific rationale or in-depth analysis to support the observed performance enhancements. The current form falls short of the originality expected for publication in Nature Communications.\n- The manuscript presents a combination of dry electrode fabrication and pre-sodiation using sacrificial sodium salts. However, the proposed strategy is conceptually similar to existing approaches and lacks distinctive novelty or innovation in mechanism or design.\n- In Figure 1a, the authors state that slurry-coated electrodes can only achieve mass loadings below 10 mg cm⁻². The authors should provide supporting evidence or references to justify the claim that electrodes with such loading cannot be fabricated using slurry-coating methods.\n- The use of sacrificial additives that undergo electrochemical decomposition may lead to gas release or structural deformation of the electrode. However, no evidence or discussion is provided regarding gas formation, porosity changes, or mechanical integrity post-decomposition.\n- A key benefit of pre-sodiation is presumed to be enhanced SEI/CEI formation. Nevertheless, the manuscript lacks critical surface characterizations such as XPS depth profiling, TOF-SIMS, or cryo-TEM to support claims related to interfacial stability and passivation.\n- While the authors assert improvements in energy density, no clear quantification is provided regarding how much sodium was compensated or how the additive influenced the cell-level metrics. Calculations and mass balancing are notably absent.\n- The fabrication method involves multi-phase blending and dry processing, which are sensitive to mixing uniformity. Yet, the manuscript offers no statistical data, such as standard deviation or reproducibility over multiple cells, to assess consistency or reliability.\n- Key design parameters such as N/P ratio, electrode loading, areal capacity, and electrode thickness are either missing or not clearly reported. This hampers the evaluation of practical feasibility and performance benchmarking.\n- Cycle life testing was conducted under a single current density and ambient temperature. The absence of tests under varied rates or thermal conditions makes it difficult to evaluate the robustness of the strategy under realistic operating environments.\n- The authors claim complete decomposition of Na₂C₂O₄, yet provide no post-mortem analysis (e.g., XRD, SEM-EDS, Raman) to confirm absence of solid residues or their effect on electrode performance. This is critical for long-term reliability.\n- In Figures 4d–f, the absolute resistance values of the dry-processed electrodes are higher than those of the wet-processed ones, regardless of pre-sodiation. The authors need to explain the reason for this higher resistance in the dry electrodes. Additionally, clarify how the dry electrodes can still exhibit better electrochemical performance despite having higher resistance even after pre-sodiation.", "reviewer_2": "The manuscript addresses the challenge of low initial Coulombic efficiency in hard carbon anodes, a significant obstacle in advancing sodium-ion battery technology. By introducing pre-sodiation via sacrificial salts, the authors present a promising approach to overcome this limitation. While conventional slurry casting methods restrict salt utilization, this study effectively demonstrates that dry-process electrode fabrication significantly improves electrical contact, enabling nearly theoretical decomposition capacities for Na₂C₂O₄. This strategy is logically sound and technically convincing, representing a meaningful advancement in developing high-performance sodium-ion batteries. Overall, the manuscript is well-written but requires some revisions. Detailed comments are provided below.\n1. The authors argue that salt aggregation occurs more readily in the slurry casting (SC) process. However, clear evidence supporting this claim is lacking. Typically, poor dispersion is considered a drawback of dry processes rather than SC methods. Could the authors clarify why dispersion is limited in the SC process? Is it related to increased surface area from reduced particle size or due to unfavorable interactions between the salt and the solvent? Additional discussion and a mechanistic explanation would strengthen this point.\n2. The manuscript states that the salt exhibits a low Young’s modulus (~70 MPa) above 100°C, which promotes deformation and thus improves dispersion. However, the connection between this mechanical property and improved dispersion remains unclear. Reference 40, cited in the manuscript, discusses enhanced contact between solid electrolytes and cathode materials due to particle deformation. The authors should clarify how salt deformability specifically influences dispersion within the context of their study.\n3. If the primary issue with the SC process is the formation of a loosely stacked structure, could increasing calendering pressure beyond the ~10 MPa used in this study further enhance particle contact? Clarifying whether this pressure selection was based on previous studies, experimental limitations, or material-specific considerations would be beneficial.\n4. The manuscript reports that the dry-process electrode (DP) exhibits a charge-transfer resistance (RCT) over 10 times greater than the SC electrode. A mechanistic explanation for this substantial difference would greatly enhance the manuscript's clarity.\n5. A critical consideration in thick electrode design is achieving uniform utilization of active material from the current collector side to the electrolyte-facing side. Effective electrolyte infiltration is essential to reduce polarization and ensure balanced reaction kinetics throughout electrode thickness. While the authors employed 2D modeling to compare behaviors at 0.1C, under higher current densities, electrolyte concentration gradients between electrode sides might intensify. Have the authors investigated how varying sacrificial salt content affects porosity and electrolyte concentration distribution? Further elaboration on why the electrolyte content was fixed at 10 wt% would be beneficial, particularly regarding whether this value was optimized and how adjusting electrolyte content might impact infiltration and overall performance.\n6. In the SC process, VGCF and Super P were used as conductive additives, whereas only VGCF was employed in the DP. Given VGCF’s known role in forming electron-conductive networks, could this have enhanced Na₂C₂O₄ decomposition in the DP? If so, can the observed differences be solely attributed to processing methods, or do conductive additive choices also contribute? Clarification on whether VGCF disperses poorly in the SC process would be helpful.\n7. In the EIS data (Fig. 4d-f), even after pre-sodiation, DP resistance remains approximately 10 times higher than SC, indicating greater ionic and charge-transfer overpotential. However, Fig. 4a shows DP voltage hysteresis is initially larger but becomes smaller than SC from the second cycle onward. Could the authors clarify this behavior? Additionally, while the manuscript mentions “effective electronic pathways” developing in DP, this seems contradictory to the high resistance shown by EIS data. A detailed explanation reconciling these findings with the proposed electronic pathway formation mechanism would greatly improve clarity.\n8. In the full-cell configuration (Fig. 6), the authors employed a DP electrode fabrication method with PTFE as the binder for the hard carbon anode. PTFE is known to decompose at potentials around 1.5 V vs. Na/Na⁺, causing irreversible capacity loss (DOI: 10.1016/j.joule.2024.01.028). This property is problematic in hard carbon systems already challenged by low initial coulombic efficiency. Although the authors attempted to address this issue via pre-sodiation, the rationale for selecting PTFE as a binder remains unclear. Could the authors clarify why PTFE was chosen and why the DP approach utilizing PTFE was preferred, despite its potential to exacerbate initial cycle coulombic inefficiency?", "reviewer_3": "In this manuscript, Qin et al. offer a robust study combining dry-processing and sacrificial salt pre-sodiation to fabricate high-performance sodium-ion batteries (SIBs). In a dry-processed electrode architecture, the authors overcome one of the utmost challenges in SIB technology—the limited initial coulombic efficiency and energy density—by using sodium oxalate (Na₂C₂O₄) as a pre-sodiation agent.\nThe experimental methods used are exhaustive and solid, such as state-of-the-art electrode fabrication through high-speed shear mixing and hot calendaring and extensive morphological, structural, and electrochemical characterization. SEM, XRD, XPS, DSC, AFM, DEMS, and EIS techniques are applied proficiently to understand how processing conditions impact the electrode structure, mechanical stability, electronic conductivity, and decomposition behavior of Na₂C₂O₄. These polymer modifications are also enhanced by 2D modeling of ion diffusion and electrolyte penetration to comprehend structural effects stemming from pre-sodiation.\nThe novelty of our work is that it shows, in the context of electrochemical co-doping based on the well-known Na₂C₂O₄ precursor, how dry-processing avoids the disadvantages associated with slurry-based methods (e.g., poor dispersion, high solvent requirements, particle agglomeration), while simultaneously achieving much better utilization of the Na₂C₂O₄ based on the production of homogeneous, conductive, and physiologically stable electrode scaffolds. The synergy renders a theoretical-level decomposition rate (400 mAh g⁻¹), enhanced porosity and ionic transport, and a significant enhancement of energy density (82.5%) and cycling life (additional 200 cycles), respectively.\nSignificantly, the authors demonstrate the practicality of their method via roll-to-roll fabrication of ultra-thick electrodes and full-cell testing using dry-processed hard carbon anodes and obtain outstanding areal capacity (5.4 mAh cm⁻²), high volumetric energy density, and excellent cycling stability. These findings set the stage for scalable, sustainable, and high-energy-density SIB production.\nI thus recommend the manuscript for publication in Nature Communications."}, "author_response": "General response to all reviewers\nWe would like to thank all reviewers for their detailed and constructive evaluation of the\nmanuscript. Based on the suggestions, we have made a number of corrections, additions and\nother improvements to the original manuscript.\nSpecifically, we added:\n(1) Additional structural and morphological characterization of the powder and\nelectrode obtained by dry-processing method (Supplementary Fig. 9: Raman of dry-\nprocessing electrode; Supplementary Fig. 10-11: SEM of material powder after dry-\nmixing);\n(2) Discussion of calendaring pressure effect on the Na C O decomposition in slurry-\n2 2 4\ncoating electrodes (Supplementary Fig. 6: SEM of slurry-coating electrodes calendared\nunder 0, 10 and 50 MPa; Supplementary Fig. 12: Potential curves in initial three cycles\nfor slurry-coating electrodes calendared under 10 and 50 MPa);\n(3) Additional test data to show reproducibility over multiple cells (Supplementary Fig.\n13-14: Potential curves of dry-processing NVP electrodes with adding 10 wt% and 20\nwt% Na C O ; Supplementary Fig. 30: Voltage curves of all-dry-processing SIBs);\n2 2 4\n(4) Evaluation of the cycle performance of all-dry-processing SIBs under high\ntemperature (Supplementary Fig. 35).\n(5) Detailed evaluation of SEI formed on hard carbon in SIB with/without pre-sodiation\n(Supplementary Fig. 32: in-depth XPS of HC electrodes; Supplementary Fig. 33-34:\nTEM of HC electrodes).\nAll changes are explained in the detailed point-by-point responses to all reviewer comments\nin the continuation of this document.\nWe hope that we have provided satisfactory responses and improved the manuscript\naccording to expectations and that the new version will be found acceptable for publication.\nSincerely yours,\nThe authors\nPoint-to-point response to reviewer comments\nReviewer #1 (Remarks to the Author):\nThis paper aims to enhance the energy density of sodium-ion batteries by simultaneously\nintroducing a dry electrode fabrication process and a pre-sodiation strategy using a sacrificial\nsalt, enabling the development of high mass-loading electrodes. However, the study primarily\nfocuses on energy density improvement by applying previously established concepts, without\nproviding sufficient scientific rationale or in-depth analysis to support the observed\nperformance enhancements. The current form falls short of the originality expected for\npublication in Nature Communications.\nAuthors’ response:\nThanks for your time and comments, which are significantly precious. We are grateful to the\nreviewer for confirming that our interphasial design strategy improves the cycling stability of\nALSMB with high areal capacity. In this work, we attempt to demonstrate at the fundamental\nlevel how high-utilization-ratio of sacrificial salts in high-mass-loading cathode can be\nsustainable obtained by integrating dry-processing and pre-sodiation. We discover that shear-\nforce, compression-force and thermal effect of dry-processing promotes formation of\nhomogenous mixture of sodium oxalate (Na C O ) with conductive agents, contributing to\n2 2 4\nintimate electronic migration pathways for complete Na C O decomposition. According to the\n2 2 4\nreviewer’s comments, we have revised, supplemented, and improved the manuscript. Below is\na detailed point-by-point response, including the innovative points, interphasial analysis, cell-\nlevel calculations and reproducibility over multiple cells.\n1. The manuscript presents a combination of dry electrode fabrication and pre-sodiation using\nsacrificial sodium salts. However, the proposed strategy is conceptually similar to existing\napproaches and lacks distinctive novelty or innovation in mechanism or design.\nAuthors’ response:\nWe appreciate the reviewer’s feedback and respectfully clarify the core innovation of our\nwork, which lies in revealing a previously unreported mechanism unique to dry processing:\nDry-processing induced salt deformation and dispersion enhancement. While pre-sodiation\nand dry electrodes are established concepts, our study is the first to demonstrate that:\n1. Shear Forces in Dry Processing Trigger Salt Plastic Deformation\nConventional solvent-based mixing cannot induce mechanical deformation of sodium salts\n(Figure R1.1). In contrast, the high-shear forces during dry mixing cause particle flattening and\nsize reduction of salts. This deformation is critical for:\n(1) Enabling uniform salt integration within the electrode matrix (Figure R1.2 d, e and f),\navoiding solvent-related agglomeration (Figure R1.1 b, f and j).\n(2) Creating intimate contact between NVP, conductive agents and Na C O powders that\n2 2 4\nenhance electron conduction pathways (Light-colored Na C O particles are evenly distributed\n2 2 4\non the surface of NVP particles in Figure R1.2 d, e and f).\n(3) Interlocking with conductive agents, forming conductive networks (Figure R1.2 g, h and\ni).\n2. Thermal Energy Synergistically Optimizes Deformation and Compact Structure\nAs revealed from high-temperature AFM test, Young’s modulus of Na C O decreases under\n2 2 4\nhigh temperature (Figure 3n-o).\n(1) The combined effect of high-speed shear-mix and generated heat during dry processing\npromotes deformation of Na C O for dispersion.\n2 2 4\n(2) The combined effect of high roller pressure and heat during hot calendaring promotes\nformation of homogeneous mixture of conductive carbon and Na C O for intimate and\n2 2 4\npermanent electrical contact.\n3. Mechanistic Distinction from Prior Art\nExisting studies focus solely on dry electrodes’ mechanical force (Nature Communications\n15, 4763 (2024) report hand-mixed and hand-rolling dry-processing electrodes, which only\ninvolves limited shear force) or pre-sodiation’s capacity compensation (employ various catalyst\nor conductive materials to enhance utilization ratio). Our work reveals a fundamental materials\nphenomenon: salt deformation under shear/compress/heat directly constructs intimate and\npermanent electron conduction for fully decomposition of Na C O . This mechanism is\n2 2 4\ninaccessible in wet processing (Figure R1.1), where solvents dissolve salts and prevent\nmechanical reshaping, and the solvent evaporation affects the dispersion of the material.\n4. Validation of Novelty\nThe revised manuscript includes:\n(1) Morphology analysis:\nNa C O particle size decreased from ~2 μm (pristine) to ~1 μm (dry-processed),\n2 2 4\nconfirming deformation (SEM in Figure R1.2).\nNa\n4\nparticles were distributed on the surface of NVP particles and inside VGCF,\nverifying the dispersibility (SEM in Figure R1.2).\nNa C O and VGCF form homogeneous mixture with consistent elemental distribution,\n2 2 4\nconfirming intimate electron conduction framework. (EDX in Figure 3i-l)\nNa C O was complete decomposed in dry-processing electrode (calculation of\n2 2 4\nsupplemented capacity and decreased mass in Supplementary Table 4-6, XRD in Figure 3b,\nXPS in Figure 3c-d, Raman in Supplementary Figure 9).\nPore size in NVP electrode were grown from ~250 nm to 1.5 μm after pre-sodiation process,\ncontributing to enhanced electrolyte infiltration (SEM in Figure 5c-d).\n(2) Young’s modulus analysis:\nYoung’s modulus of Na C O decreased to 71.3 and 30.3 MPa at 100 and 150 °C compare\n2 2 4\nto 609.7 MPa at 25 °C, confirming thermal energy synergistically deformation (Figure 3n-o).\n(3) Performance correlation:\nDry-processing electrode after pre-sodiation achieved 59% higher average electrolyte\nconcentration and 5.8% higher average sodium concentration in NVP, confirming enhanced\nkinetics of electrodes by integrating dry-processing and pre-sodiation (2D COMSOL simulation\nin Figure 5j-n).\nPerformances were tested using multiple cells to verify reproducibility. (Supplementary\nFigure 13-15, 29, 31).\nStructure and composition of SEI on HC electrodes were evaluated to show the effect of\npre-sodation on interfacial stability. (TEM and XPS of HC in Supplementary Figure 32-34)\nOur strategy transcends a \"simple combination\" by uncovering and leveraging a new\nphysical mechanism—dry-processing-induced salt deformation—to solve dispersion and\ninterfacial challenges intrinsic to sacrificial salts.\nFigure R1.1. Sectional morphology of slurry-coating electrode calendared under different\npressure. a-b, Electrode without calendaring. c-d, Images of pressure sensitive paper to show\nthe calendaring pressure. e-f, Sectional morphology of slurry-coating electrode calendared\nunder 10 MPa. g-h, Sectional morphology of slurry-coating electrode calendared under 10 MPa\nafter charging to 4.5 V. i-j, Sectional morphology of slurry-coating electrode calendared\nunder 50 MPa. k-l, Sectional morphology of slurry-coating electrode calendared under 50 MPa\nafter charging to 4.5 V. Na C O is highlighted in yellow, and conductive materials are highlighted\n2 2 4\nin red\nFigure R1.2. Effect of dry-mixing on dispersion and deformation of Na C O . a-b, Morphology\n2 2 4\nof the original ball-milled Na C O . c, Morphology of the NVP particles. d-i, Morphology of\n2 2 4\nNVP, VGCF and Na C O powder after dry-mixing at a speed of 18000 rpm.\n2 2 4\nRevisions made to the manuscript:\nIn the revised manuscript, we added the novelty statement in the introduction part (on page\n5): “While dry electrode fabrication and sacrificial salts have been separately reported, this\nwork reveals a previously overlooked synergy: mechanical shear and thermal energy during dry\nprocessing induce plastic deformation of salts, fundamentally enabling their uniform dispersion\nand interfacial optimization.”\n2. In Figure 1a, the authors state that slurry-coated electrodes can only achieve mass loadings\nbelow 10 mg cm⁻². The authors should provide supporting evidence or references to justify the\nclaim that electrodes with such loading cannot be fabricated using slurry-coating methods.\nAuthors’ response:\nWe sincerely thank the reviewer for this valid critique. We acknowledge that slurry-coated\nelectrodes can achieve loadings >10 mg cm⁻². However, our original statement aimed to\nhighlight the practical limitations for electrodes containing sacrificial sodium salts, which are\nessential for application of pre-sodiation. Table R1.1 compiles references in past 5 years on\nslurry-coated cathodes with sacrificial salts. The reported electrodes show loadings ≤10 mg\ncm⁻². The only exception (17 mg cm⁻², Energy Storage Materials 68, 103318 (2024)) was coated\nsacrificial salts layer on the surface of pre-coated slurry-coating electrode, which involves\nadditional solvent evaporation process and might cause structural damage to the pre-coated\nactive layer. To clarify and substantiate this claim, we have revised the statement in Figure\n1a to explicitly specify the context.\nTable R1.1. Comparison of state-of-art sacrificial additives and corresponding cathode\nproperties.\nLoading /\nAdditives Electrode Ref\nmg cm2\nEDTA-4Na mix-slurry coating 3.5 1\nNa C O mix-slurry coating 5.6 2\n2 4 4\nNaCrO surface-slurry coating 2.9 3\nNa C O mix-slurry coating 4.8 5\n2 2 4\nNa C O mix-slurry coating 4.6 6\n3 6 7\nNa\nNaC O mix-slurry coating 2.5 7\n2 2\n1,2,4-triazole sodium 8\nmix-slurry coating 8\n(TS)\nNa O-NiO mix-slurry coating 2 9\n2 4 5\nNaC O mix-Dry processing 11.1 11\n2 2\nLi C O surface-slurry coating 1.3 12\n2 2 4\nLi C O -CNT surface-slurry coating 7 13\n2 4 4\nR-Li CO @SPC mix-slurry coating 10 14\n2 3\nLi\nLi C O -Ni/N-rGO mix-slurry coating 3 15\n2 2 4\nMoC1-x/NC-Li C O surface-slurry coating 17 16\n2 2 4\nCo-Li CO @LCO mix-slurry coating 2.5 17\n2 3\nThis\nNa C O mix-Dry processing 53.88\n2 2 4\nwork\nRevisions made to the manuscript:\nIn the revised manuscript, we have revised the inappropriate statement in Figure 1a (on page\n4). “Limited mass loading (<10 mg cm-2, <1 mAh cm-2)” has been revised as “Limited mass\nloading with sacrificial salts (<10 mg cm-2, <1 mAh cm-2)”\nFigure 1. Schematic illustration of production and structure of electrodes using slurry-coating\nand dry-processing electrode, respectively.\n3. The use of sacrificial additives that undergo electrochemical decomposition may lead to gas\nrelease or structural deformation of the electrode. However, no evidence or discussion is\nprovided regarding gas formation, porosity changes, or mechanical integrity post-\ndecomposition.\nAuthors’ response:\nWe appreciate the reviewer's insightful comment. We confirm that the majority of requested\nevidence was already provided in the original manuscript (Part2#: Function Mechanisms of\nthe DP electrodes on Na\n4\ndecomposition, Part4#: Effect of sacrificial Na\n4\npre-\nsodiation on DP cathode). Below we clarify the location of existing data and add analyses to\nstrengthen the discussion.\n1. Gas Release Monitoring\nDEMS in Figure 3a quantitatively shows the correlation between electrode potential and\ndynamic CO₂ evolution rate. DP electrode shows larger plateau capacity accompanied by a\nlonger CO production period compared to SC electrode, implying a greater proportion of the\n2 2 4\n2. Porosity Changes\nThe pore sizes of the electrodes were compared by observing the surface and cross-sectional\nmorphologies (Figure 3e-l, Figure 5c-d, Supplementary Fig. 20, 23-25). The porosity\nchanges before and after Na\n4\nelectrochemical decomposition were calculated by the mass\nand volume of the electrodes before and after charge and discharge, which is summarized in\nFigure 5e-h, Supplementary Fig. 19 and Supplementary Table 2, 9. Compare to less porosity\nchanges (increased by 2.91%) in slurry-coating electrodes, DP electrodes show a significant\nreduced compacted densities from 1.61 to 1.41 g cm-3, of which the porosity increased from\n45.91% to 53.84%, attributing to the fully sacrificial salts decomposition.\n3. Mechanical Integrity Validation\nThe fibrillar PTFE network acts as a ‘mechanical skeleton’ that prevents structural collapse.\nCross-sectional morphology observations over a wide range and at multiple locations confirm\nthe mechanical integrity of the dry electrode after sodium oxalate decomposition, as shown in\nFigure 5a-b, Supplementary Fig. 22, 25 and 26.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the discussion on gas evolution (on page 10):\n“Moreover, DP electrode shows larger plateau capacity accompanied by a longer CO\n2\nproduction period compared to SC electrode, implying a greater proportion of the Na C O has\n2 2 4\ndecomposed in DP electrodes”\n4. A key benefit of pre-sodiation is presumed to be enhanced SEI/CEI formation. Nevertheless,\nthe manuscript lacks critical surface characterizations such as XPS depth profiling, TOF-SIMS,\nor cryo-TEM to support claims related to interfacial stability and passivation.\nAuthors’ response:\nWe sincerely appreciate the reviewer’s insightful feedback, and we are sorry for the\ninsufficient presentation of relevant information regarding interfacial characterization. To\naddress the reviewer’s concerns, we have now incorporated comprehensive surface/interface\nanalyses in the revised manuscript (Supplementary Fig. 32-34), specifically addressing the\nimpact of pre-sodiation on SEI properties through depth-resolved XPS and TEM. We sincerely\napologize for choosing the ordinary SEI characterization method, as TOF-SIMS and cryo-TEM\nis too expensive and limited experimental condition for conducting these experiments.\nFortunately, these data can also clearly provide direct evidence of improved interfacial\npassivation.\nAr⁺ sputtering was employed to quantitatively analyze compositional gradients across the\nSEI layer on HC electrodes. The atomic concentrations are calculated from XPS spectra and\ncompared in Figure R1.3a-c. Compared to HC electrode in SIB without pre-sodiation, the HC\nelectrode in SIB with pre-sodiation shows the lower C and O atomic ratio but higher Na atomic\nratio, indicating lower proportion of organic species but high proportion of inorganic species\nfor the SEI formed under influence of Na\n4\ndecomposition. XPS spectra were deconvoluted\nto reveal the detailed composition in Figure R1.3d-i. The C 1s XPS spectra revealed that the\nSEI contains abundant peaks corresponding to C-C (284.8 eV), C-O (286.5 eV), and CO 2-\n3\n(288.5 eV) and PTFE-related C-F peaks (290.9 and 292.58 eV). The prominent intensity of the\nC-O peak on the surface and inner layer in Figure R1.3d indicates that a high proportion of\norganic components was generated on the hard carbon surface without pre-sodiation. By\ncontrast, pre-sodiation treated HC electrodes shows low proportion of C-O but high proportion\nof CO 2- throughout the XPS test depth. The normalized content of C-O and CO 2- calculated\n3 3\nbased on the peak area in C 1s is summarized in Figure R1.3j. SEI formed with pre-sodation\ntreatment shows a Na CO content of more than 20% and a C-O content of less than 5%; while\n2 3\nthe SEI formed without pre-sodiation show a higher content of C-O than Na CO . Similar\n2 3\ncontent relationship is founded in O 1s spectra in Figure R1.3e, h and k, where SEI formed\nwith pre-sodation treatment had a higher proportion of inorganics (CO 2- and Na O) and a lower\n3 2\nC-O content. These results collectively indicate that a Na CO -rich SEI was formed under\n2 3\ninfluence of Na C O decomposition, which may be derived from the reaction of the generated\n2 2 4\nCO on the HC/electrolyte interface and lower potential by sodium supplementation. The F 1s\n2\nspectra were deconvoluted in Figure R1.3f and i, which contain two peaks corresponding to C-\nF and NaF. The HC electrodes both show larger F contents in inner SEI and similar peak area\nof NaF, indicating the F-containing species formed in early-stage of SEI. For the hard carbon\nelectrodes in our studies, F comes from PTFE and FEC, of which the decomposition potentials\nare both higher than 1 V vs Na/Na+ [1,2], indicating that PTFE and FEC decomposed before\nNa C O electrochemical decomposition. Therefore, these results indicate that the Na C O\n2 2 4 2 2 4\ndecomposition did not affect the generation process of F-related substances.\nReference:\n[1] Removing electrochemical constraints on polytetrafluoroethylene as dry-process binder for\nhigh-loading graphite anodes. Joule, 2024, 8(5): 1350-1363.\n[2] Weakly solvating ester electrolyte for high voltage sodium-ion batteries. Nano Energy, 2024,\n128: 109969.\nFigure R1.3. Depth-resolved XPS measurements for HC electrodes in SIB with/without pre-\nsodiation. a, XPS spectra of HC electrodes. b, Atomic concentration of C, O, F, Na of HC\nelectrode in SIB without pre-sodiation. c, Atomic concentration of C, O, F, Na of HC electrode\nin SIB with pre-sodiation. d-f, C 1s, O 1s and F 1s spectra of HC electrode in SIB without pre-\nsodiation. g-i, C 1s, O 1s and F 1s spectra of HC electrode in SIB without pre-sodiation. j,\nNormalized contents of CO 2- and C-O in C 1s spectra. k, Normalized contents of inorganics\n3\n(CO 2- and Na O) and C-O in O 1s spectra.\n3 2\nMorphologies and components of SEIs with/without pre-sodiation treatment were further\nevaluated using TEM. Figure R1.4a-f show the EDS mapping results of SEI formed on HC\nelectrode without pre-sodiation treatment, where O, F and Na signals are enriched at the outer\nshell of HC particles. However, in the enlarged image of the SEI, only a small amount of\ninorganic grains are observed dispersed outside the HC particles. Based on the lattice spacing\nmeasurement in Figure R1.4h-i, these inorganic particles are NaF and Na CO , with sodium\n2 3\ncarbonate being the main component. Figure R1.4j-l shows an additional area of the SEI, where\nSEI does not completely cover the HC boundary and several Na CO grains are dispersed in\n2 3\nSEI. By contrast, Figure R1.5 shows that a large number of white bright spots appear in the\nHAADF image, and the O, F, and Na elements are distributed around the HC boundary,\nindicating that an inorganic-rich and fully covered SEI film is formed on the HC electrode after\npre-sodiuation treatment. The inorganic particles are Na CO and Na O, verified by the lattice\n2 3 2\nspacing in FFT and inverse FFT images in Figure R1.5h-i. These results are consistent with in-\ndepth XPS result, which shows higher inorganic contents in SEI formed with pre-sodiation\ntreatment. Similar interfacial morphology is observed at another area on HC electrodes in\nFigure R1.5j-l. Inorganic nanoparticles with size of ~10 nm are closely arranged at the\nboundary of HC, which form a dense and complete protective layer for enhanced interfacial\nstability.\nFigure R1.4. Characterization of solid electrolyte interphase formed on HC electrodes in SIB\nwithout pre-sodiation. a-f, HAADF and corresponding EDX mapping. g, Enlarged area of SEI\nto show the inorganic compounds. h-i, FFT and inverse FFT images of the inorganic particles\nin f. j-l, Additional position of SEI and corresponding FFT image.\nFigure R1.5. Characterization of solid electrolyte interphase formed on HC electrodes in SIB\nwith pre-sodiation. a-f, HAADF and corresponding EDX mapping. g, Enlarged area of SEI to\nshow the inorganic compounds. h-i, FFT and inverse FFT images of the inorganic particles in\nf. j-l, Additional position of SEI and corresponding FFT image.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the depth-resolved XPS and TEM (Figure R1.3-\n1.5) in revised Supplementary Information as Supplementary Figure 32-34, and added\ncorresponding discussion on SEI in revised main text (on page 21): “The improved interfacial\npassivation and stability by pre-sodiation were further investigated by analyzing the\ncomposition and structure of SEI on HC electrodes (Supplementary Fig. 32-34). Depth-\nresolved XPS and TEM collectively indicate that a Na CO -rich SEI was formed under\n2 3\ninfluence of Na C O decomposition, which are closely arranged at the boundary of HC,\n2 2 4\ncontributing to a dense and complete protective layer for enhanced interfacial stability. By\ncontrast, SEI formed without pre-sodiation treatment is organic-rich and does not completely\ncover the HC boundary.”\n5. While the authors assert improvements in energy density, no clear quantification is provided\nregarding how much sodium was compensated or how the additive influenced the cell-level\nmetrics. Calculations and mass balancing are notably absent.\nAuthors’ response:\nThanks for the reviewer’s insightful comments. In the revised manuscript (Supplementary\nTable 10-11), we have added detailed calculations, mass balancing, and cell-level modeling to\nquantitatively validate the impact of pre-sodiation on energy density. Table R1.2 summarized\nthe mass and capacity parameters of two groups of all-dry-processing SIBs in rate and cycle\ntests. For ~5.5 mAh cm-2 NVP electrode containing 10 wt% Na C O , 2.13 mAh cm-2 sodium\n2 2 4\ncan be compensated by electrochemical decomposition of Na C O . The all-dry-processing\n2 2 4\nSIBs with pre-sodiation exhibit reversible specific capacity of 101.52 and 103.81 mAh g-1,\ncorresponding to 94.68% and 94.10% of the reversible capacity of NVP, respectively.\nTable R1.2. Summary of the cell metric of all-dry-processing SIB\nRate test Cycle test\nSIB without SIB with SIB without SIB with\npresodiation presodiation presodiation presodiation\nOverall cathode mass / mg 70.94 72.95 72.72 75.09\nNVP mass / mg 58.04 59.68 59.49 61.43\nNVP mass loading / mg cm-2 51.36 52.81 52.65 54.36\nCathode reversible areal\n5.51 5.67 5.81 6.00\ncapacity / mAh cm-2\nCathode thickness / um 410 425 410 425\nOverall anode mass / mg 33.32 33.45 33.62 34.00\nHC mass / mg 31.65 31.78 31.94 32.30\nHC mass loading / mg cm-2 23.80 23.89 24.01 24.29\nAnode reversible areal\n6.72 6.74 6.78 6.85\ncapacity / mAh cm-2\nAnode thickness / um 300 300 300 300\nN/P ratio 1.22 1.19 1.17 1.14\nNa C O mass / mg 0.00 6.63 0.00 6.83\n2 2 4\nCell charge specific capacity\n107.22 162.28 110.32 179.48\n/ mAh g-1\nCell charge capacity / mAh\n5.51 8.57 5.81 9.76\ncm-2\nCell discharge specific\n63.51 97.72 67.65 92.80\ncapacity / mAh g-1\nCell discharge capacity /\n3.00 5.16 3.56 5.05\nmAh cm-2\nCoulombic efficiency / %\n54.39 60.21 61.27 51.74\nCell reversible\n62.91 101.52 65.18 103.81\ncapacity@0.1C / mAh g-1\nCell reversible\n3.23 5.36 3.43 5.64\ncapacity@0.1C / mAh cm-2\nDischarge energy / Wh 0.0107 0.0185 0.0114 0.0197\nCompensated capacity /\n- 2.13 - 2.21\nmAh cm-2\nEquivalent Capacity of\n- 362.93 - 365.83\nNa C O / mAh g-1\n2 2 4\nBased on the cell metric in Table R1.2, the influence of Na C O on the cell-level metrics\n2 2 4\nwere calculated based on model reported by Meng’s group [1]. Na C O pre-sodiation treatment\n2 2 4\neffectively enhanced the energy density at cell-level. Specifically, single-layer pouch cell with\npre-sodiation could deliever energy density of 151.74 Wh kg-1 and 187.90 Wh L-1, which is\n59.66% and 69.49% higher than that of pouch cell without pre-sodiation.\nTable R1.3. Maximum energy density estimation of an all-dry-processing sodium ion battery’s\nsingle-layer pouch cell based on electrode performance\nSIB without\nSIB with presodiation\npresodiation\nOperating Voltage / V 2-3.8 V 2-3.8 V\nTotal area / cm2 5(cathode), 5.94(anode) 5(cathode), 5.94(anode)\nCapacity / mAh 17.15 28.2\nNP ratio / Frac 1.17 1.14\nCathode active mass ratio / Frac 0.9 0.9\nCathode capacity / mAh g-1 110.32 110.32\nCathode active materials mass / g 0.26324 0.27182\nBinder and carbon ratio / Frac 0.1 0.1\nBinder and carbon mass / g 0.02925 0.03020\nCathode thickness / um 410 425\nCathode mass / g 0.29249 0.30202\nNa C O mass / mg 0 0.03020\n2 2 4\nGenerated CO mass / mg 0 0.01983\nAnode active mass ratio / Frac 0.95 0.95\nAnode capacity / mAh g-1 282.16 282.16\nAnode active materials mass / g 0.14264 0.14426\nBinder and carbon ratio / Frac 0.05 0.05\nBinder and carbon mass / g 0.00751 0.00759\nAnode thickness / um 300 300\nAnode mass / g 0.15015 0.15185\nAnode areal capacity / mAh cm-2 6.78 6.85\nLiquid electrolyte ratio / g Ah-1 2 2\nRequired electrolyte / g 0.0343 0.0564\nSeparator mass areal density / mg cm-2 1.386 1.386\nSeparator thickness / um 16 16\nSeparator area / cm2 6 6\nRequired separator mass / g 0.00832 0.00832\nCarbon-coated Al thickness / um 20 20\nCarbon-coated Al areal density / mg cm-2 4.16 4.16\nRequired Carbon-coated Al foil area / cm2 10.94 10.94\nRequired Carbon-coated Al foil mass / g 0.04551 0.04551\nTotal mass / g 0.53077 0.57447\nVolume / L 0.000455004 0.000463914\nDischarge energy / Wh 0.0504 0.0872\nEnergy density of single-layer pouch cell / Wh kg-1 95.04 151.74\nEnergy density of single-layer pouch cell / Wh L-1 110.86 187.90\nPackage and tab mass are excluded.\nDensities of binder&carbon, separator and carbon-coated Al foil are referring to literature [1].\nReference:\n[1] A 5 V-class cobalt-free battery cathode with high loading enabled by dry coating. Energy &\nEnvironmental Science 16, 1620-1630 (2023).\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the detailed calculations (Table R1.2-1.3) in revised\nSupplementary Information as Supplementary Table 10-11.\n6. The fabrication method involves multi-phase blending and dry processing, which are\nsensitive to mixing uniformity. Yet, the manuscript offers no statistical data, such as standard\ndeviation or reproducibility over multiple cells, to assess consistency or reliability.\nAuthors’ response:\nWe thank the reviewer for highlighting this critical aspect of process validation. In the revised\nmanuscript, we have now added comprehensive analyses across multiple independent electrode\nbatches to rigorously quantify the reproducibility of our dry-processing electrodes.\nSpecifically, Figure R1.6 shows effect of calendaring pressure on the Na C O\n2 2 4\ndecomposition in slurry-coating electrodes, which contain results from 4 retested batteries.\nFigure R1.7 shows potential curves of dry-processing NVP electrodes with adding 10 wt%\nNa C O , which contain results from 3 retested batteries. Figure R1.8 shows potential curves\n2 2 4\nof dry-processing NVP electrodes with adding 20 wt% Na C O , which contain results from 4\n2 2 4\nretested batteries. Figure R1.9 shows voltage curves of all-dry-processing SIBs with adding 10\nwt% Na C O in cathode, which contain results from 4 retested batteries.\n2 2 4\nMoreover, Supplementary Fig. 24-25 compared morphology of three different area in the\nsectional SEM image of NVP electrodes, which show similar characteristic of pore structure.\nThe morphology of dry-processing NVP electrodes containing 20wt% Na C O were evaluated\n2 2 4\nand added in the revised manuscript as Supplementary Fig. 26, where the element distribution\nand pore characteristics of three different regions in the thickness direction of the electrode are\ncharacterized to show the consistency.\nThese results from electrochemical and spectroscopic characterization conclusively\ndemonstrates that the dry-process method using ultra-high-speed blending delivers electrodes\nwith <5% performance variability across batches, resolving concerns about blending sensitivity\nand establishing its reliability for scalable manufacturing.\nFigure R1.6. Effect of calendaring pressure on the Na C O decomposition in slurry-coating\n2 2 4\nelectrodes. a-b, Potential curves in initial three cycles for slurry-coating electrodes calendared\nunder 10 MPa. c-d, Potential curves in initial three cycles for slurry-coating electrodes\ncalendared under 50 MPa.\nFigure R1.7. Potential curves of dry-processing NVP electrodes with adding 10 wt% Na C O\n2 2 4\nto show repeatability.\nFigure R1.8. Potential curves of dry-processing NVP electrodes with adding 20 wt% Na C O\n2 2 4\nto show repeatability.\nFigure R1.9. Voltage curves of all-dry-processing SIBs with adding 10 wt% Na C O in\n2 2 4\ncathode to show repeatability.\nTable R1.4. Mass change and pre-sodiation capacity of slurry-coating electrodes with adding\n10% Na C O in initial cycle\n2 2 4\nNa C O NVP mass\n2 2 4\norigin Na C O 4.5 V decrease decomposition\n2 2 4\nspecific loading\n/ mg mass / mg mass / mg mass / mg ratio / %\ncapacity / mg cm-2\n0# 17.17 1.03 14.70 0.64 62.00 248.00 10.3\n1# 16.76 1.00 14.34 0.62 62.26 249.05 8.81\n2# 16.88 1.01 14.46 0.61 60.65 242.62 8.90\n3# 16.71 0.99 14.30 0.62 62.52 250.09 8.78\n4# 17.30 1.04 14.82 0.64 61.52 246.07 9.21\nTable R1.5. Mass change and pre-sodiation capacity of dry-processing electrodes with adding\n10% Na C O in initial cycle\n2 2 4\nNa C O NVP mass\n2 2 4\norigin Na C O 4.5 V decrease decomposition\n2 2 4\nspecific loading\n/ mg mass / mg mass / mg mass / mg ratio / %\ncapacity / mg cm-2\n0# 74.42 6.77 62.03 6.75 99.82 399.28 53.88\n1# 70.52 6.41 58.77 6.41 99.92 399.68 51.06\n2# 73.75 6.70 61.47 6.70 99.89 399.56 53.40\n3# 73.91 6.72 61.61 6.71 99.80 399.20 53.51\n4# 69.39 6.31 57.83 6.31 99.95 399.80 50.24\nTable R1.6. Mass change and pre-sodiation capacity of dry-processing electrodes with adding\n20% Na C O in initial cycle\n2 2 4\nNa C O NVP mass\n2 2 4\norigin Na C O 4.5 V decrease decomposition\n2 2 4\nspecific loading\n/ mg mass / mg mass / mg mass / mg ratio / %\ncapacity / mg cm-2\n1# 70.94 11.82 59.29 11.65 98.57 394.28 47.08\n2# 71.55 11.93 59.90 11.65 97.72 390.88 47.49\n3# 76.36 12.73 64.08 12.28 96.49 385.96 50.68\n4# 70.37 11.73 58.82 11.55 98.50 394.00 46.71\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the data over multiple cells (Figure R1.6-1.9) in\nrevised Supplementary Information as Supplementary Figure 12-14, 30. The corresponding\ndata table (Table R1.4-R1.6) has been added in the revised Supplementary Information as\nSupplementary Table 4-6. And the Figure 4b have been revised to show performance\nvariability across electrodes (Main text, page 14).\nFigure 4. … b, Literature summary of pre-sodiation/lithiation cathode using sacrificial\nadditives by cathode mass loading and decomposition capacity of additives. …\n7. Key design parameters such as N/P ratio, electrode loading, areal capacity, and electrode\nthickness are either missing or not clearly reported. This hampers the evaluation of practical\nfeasibility and performance benchmarking.\nAuthors’ response:\nWe sincerely apologize for the lack of clarity in reporting critical cell design parameters in\nthe original manuscript. We agree that these metrics are essential for evaluating practical\nfeasibility and benchmarking. To resolve this, we have added a dedicated battery parameter\ntable in Supplementary Information of the revised manuscript, consolidating all key\nfabrication and design specifications.\nTable R1.2. Summary of the cell metric of all-dry-processing SIB\nRate test Cycle test\nSIB without SIB with SIB without SIB with\npresodiation presodiation presodiation presodiation\nOverall cathode mass / mg 70.94 72.95 72.72 75.09\nNVP mass / mg 58.04 59.68 59.49 61.43\nNVP mass loading / mg cm-2 51.36 52.81 52.65 54.36\nCathode reversible areal\n5.51 5.67 5.81 6.00\ncapacity / mAh cm-2\nCathode thickness / um 410 425 410 425\nOverall anode mass / mg 33.32 33.45 33.62 34.00\nHC mass / mg 31.65 31.78 31.94 32.30\nHC mass loading / mg cm-2 23.80 23.89 24.01 24.29\nAnode reversible areal\n6.72 6.74 6.78 6.85\ncapacity / mAh cm-2\nAnode thickness / um 300 300 300 300\nN/P ratio 1.22 1.19 1.17 1.14\nNa C O mass / mg 0.00 6.63 0.00 6.83\n2 2 4\nCell charge specific capacity\n107.22 162.28 110.32 179.48\n/ mAh g-1\nCell charge capacity / mAh\n5.51 8.57 5.81 9.76\ncm-2\nCell discharge specific\n63.51 97.72 67.65 92.80\ncapacity / mAh g-1\nCell discharge capacity /\n3.00 5.16 3.56 5.05\nmAh cm-2\nCoulombic efficiency / %\n54.39 60.21 61.27 51.74\nCell reversible\n62.91 101.52 65.18 103.81\ncapacity@0.1C / mAh g-1\nCell reversible\n3.23 5.36 3.43 5.64\ncapacity@0.1C / mAh cm-2\nDischarge energy / Wh 0.0107 0.0185 0.0114 0.0197\nCompensated capacity /\n- 2.13 - 2.21\nmAh cm-2\nEquivalent Capacity of\n- 362.93 - 365.83\nNa C O / mAh g-1\n2 2 4\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the detailed calculations (Table R1.2) in revised\nSupplementary Information as Supplementary Table 10.\n8. Cycle life testing was conducted under a single current density and ambient temperature. The\nabsence of tests under varied rates or thermal conditions makes it difficult to evaluate the\nrobustness of the strategy under realistic operating environments.\nAuthors’ response:\nWe appreciate the reviewer’s valid point regarding the need for multi-condition validation to\nassess practical viability. At our areal capacity of 5.5 mAh cm-2, 0.2 C corresponds to 1.1 mA\ncm-2 - already exceeding the current densities in most literature (typically 0.1-0.5 mA cm-2 at\n0.2-1.3 mAh cm-2, as summarized in Supplementary table 12). Further increasing to 0.5 C (2.64\nmA cm-2) would induce severe polarization (Figure 6c), reducing usable capacity to 60 mAh g-\n1 and invalidating cycle life metrics. This aligns with industry norms where high-loading\nelectrodes prioritize energy density over ultra-high-rate cycling. In the revised manuscript,\nextended cycling at 0.3 C were added in Figure 6b. Specifically, SIB with pre-sodiation\nmaintain high capacity of 74.12 mAh g-1 after 50 cycles test coupling multi-rate and 0.3 C\ncycling (1.58 mA cm-²), comparing to specific capacity of 49.53 mAh g-1 for SIB without pre-\nsodiation. Moreover, according to suggestion from reviewer, high-temperature cycling\ntest (40 °C at 0.1C or 0.2C) have been added in revised manuscript, as shown in Figure R1.10.\nSpecifically, SIB with pre-sodiation retained 80.3% and 77.2% capacity after 30 cycles under\ncurrent densities of 0.1 C and 0.2 C, respectively, further verifying the interfacial stability.\nFigure R1.10. Cycling stability under 40 °C. a, Capacity during cycling. b, Voltage curves of\nSIB cycling at a current density of 0.1 C. c, Voltage curves of SIB cycling at a current density\nof 0.1 C.1 C=100 mA g-1.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the high-temperature cycling test (Figure R1.10)\nin revised Supplementary Information as Supplementary Fig. 35 and added corresponding\ndiscussion in revised main text (on page 21):\"Moreover, high-temperature cycling test (40 °C)\nwere tested to verify the interfacial stability in Supplementary Fig. 35, where SIB with pre-\nsodiation retained 82.3% and 77.2% capacity after 30 cycles under current densities of 0.1 C\nand 0.2 C, respectively.\"\n9. The authors claim complete decomposition of Na₂C₂O₄, yet provide no post-mortem analysis\n(e.g., XRD, SEM-EDS, Raman) to confirm absence of solid residues or their effect on electrode\nperformance. This is critical for long-term reliability.\nAuthors’ response:\nWe thank the reviewer for highlighting the need for direct evidence of complete Na₂C₂O₄\ndecomposition. The original manuscript included XRD, XPS data on electrode surface and\nSEM-EDS data on electrode cross section (Figure 3b-d, Figure 3i-l), which collectively\nconfirm the absence of bulk residues from chemical bonds detection and elemental distribution.\nMain text (page 10): “Moreover, DP electrode shows larger plateau capacity accompanied\nby a longer CO production period compared to SC electrode, implying a greater proportion of\n2\nthe Na C O has decomposed in DP electrodes, which were further verified using X-ray\n2 2 4\ndiffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests. Fig. 3b depicts the XRD\npatterns of SC and DP electrodes after charging to different potentials, which are as prepared,\nto 3.8 V and to 4.5 V. The (410) diffraction peak of Na C O is chosen to clearly show the\n2 2 4\nresidual phases without interference by the signal from NVP, which locates at 2θ=38.541° and\nhighlighted using orange star. Compared with persistent (410) peak in SC electrodes, the (410)\ndiffraction peak of Na C O in DP electrodes decreases in intensity as charged to 3.8V and\n2 2 4\nvanish entirely as charged to 4.5 V, which verifies the completely consumption of Na C O in\n2 2 4\nDP electrodes. XPS spectra in Fig. 3c-d further corroborates the evolution process observed in\nthe XRD patterns. In C 1s and O 1s spectra, the intensity of C=O bond (289 eV, 531.7 eV) in\nSC electrodes slightly decreased and maintained a high intensity as charged to 4.5 V, indicating\nthat there were residual Na C O in the SC electrodes. In contrast, C=O signal vanishes in C\n2 2 4\n1s spectra and largely reduced in O 1s spectra for DP electrodes charged to 4.5 V, again\nconfirming the completely decomposition of Na C O in DP electrodes. The intensities of\n2 2 4\ncharacteristic peaks ascribed to Na C O decreased as charging to 3.8 V for both SC and DP\n2 2 4\nelectrodes, which is in consistency with that the decomposition of Na C O starts before 3.8 V\n2 2 4\nin Fig. 3a. In short, complete Na C O decomposition is achieved in dense DP electrodes other\n2 2 4\nthan in loose SC electrodes, which shows a reduced reaction overpotential and a larger\ncapacity.”\nMain text (page 11): “The sectional structure was compared to figure out Na C O\n2 2 4\ndistribution inside the DP electrodes. As shown in Fig. 3i, dense electrode structure with two\nkinds of contrast is observed in the section of DP electrodes. According to V and C distribution\nin Fig. 3j, the light and dark phases are NVP and conductive carbon, respectively. Importantly,\nthere is no polyhedron-shaped Na C O particle, while obvious Na signals are observed\n2 2 4\ndistributed in the gap between NVP particles. This Na signal is highly consistent with the C\nsignal, indicating that DP method produces a homogeneous mixture consisting of conductive\ncarbon and Na C O , thus establishing an intimate and permanent electrical contact. Hence,\n2 2 4\ncomplete Na C O decomposition is achieved as DP electrodes charging to 4.5 V, showing that\n2 2 4\nthe Na signal comes only from the NVP particles, which is the same distribution with the V, O,\nand P signal”\nFigure R1.11. (Figure 3 in Main text) Characterization of Na C O in cathode before and after\n2 2 4\npresodiation. a, Gas analysis during initial charging process. b, XRD pattern and c-d, C 1s and\nO 1s XPS spectra of NVP electrodes after charging to different potentials. e-f, Morphology and\nEDX mapping of surface of SC electrodes charged to 4.5 V. The scale bar is 5 μm in Fig. 3f. g-\nh, SEM images of section structure of SC electrodes charged to 4.5 V. i-l, Morphology and\nEDX mapping of section structure of DP electrodes before and charged to 4.5 V. The scale bar\nis 5 μm in Fig. 3j and 3l.\nTo address this conclusively, we have also performed Raman on electrode cross-\nsection. Figure R1.12 a-b show the spot position of Raman tests, surrounding the spherical\nNVP particles. According to reference [1-2], Na C O exhibit characteristic peaks located at\n2 2 4\n~1358, ~1455 and ~1643 cm-1, which ascribe to ν (C-O)+ δ(O-C=O), ν (C-O)+ ν(C-C) and\nS S\nν (C=O), respectively. However, the analysis of the Raman signal of Na C O is disturbed by\na 2 2 4\nthe pronounced D (~1350 cm-1) and G (~1580 cm-1) peaks of the VGCF. Nevertheless, peaks\nin the gray box in the initial state (Fig. R1.12c), which might ascribe to ν (C-O)+ ν(C-C) of\nS\nNa C O , disappeared after charging to 4.5 V (Fig. R1.12d), verifying the complete\n2 2 4\ndecomposition of Na C O .\n2 2 4\nTherefore, for the mixed structure of Na C O and VGCF in this work, Raman is not suitable\n2 2 4\nto accurately analyze whether there are Na C O residues in the electrode; while in the original\n2 2 4\ntext, we have demonstrated the complete decomposition of Na C O using XRD, XPS and\n2 2 4\nSEM-EDX.\nFigure R1.12. Raman spectra of dry-processing electrodes before (a, c) and after (b, d) pre-\nsodiation, which were tested on four positions on the Ar+-polished cross section. a-b, Optical\nimages to show the positions of Raman tests. c-d, Corresponding Raman spectra.\nReference:\n[1] Effect of thermal annealing on synthetic sodium oxalate crystals. Journal of Analytical and\nApplied Pyrolysis, 2011, 91(2): 332-337.\n[2] Raman spectroscopy of natural oxalates. Analytica Chimica Acta, 2004, 517(1-2): 207-214.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the Raman test on cross section of dry-processing\nelectrode (Figure R1.12) in revised Supplementary Information as Supplementary Fig. 9 to\nsupport the complete decomposition of Na₂C₂O₄ in dry-processing electrode.\n10. In Figures 4d–f, the absolute resistance values of the dry-processed electrodes are higher\nthan those of the wet-processed ones, regardless of pre-sodiation. The authors need to explain\nthe reason for this higher resistance in the dry electrodes. Additionally, clarify how the dry\nelectrodes can still exhibit better electrochemical performance despite having higher resistance\neven after pre-sodiation.\nAuthors’ response:\nWe thank the reviewer for this insightful observation. The higher absolute impedance in dry-\nprocessed electrodes (410 μm thickness, ~5.5 mAh cm-2 areal capacity) versus wet-processed\ncounterparts (84 μm, ~1.1 mAh cm-2) is primarily attributable to differences in electrode\nthickness. According to electrochemical theory, total impedance scales proportionally with\nelectrode thickness due to elongated ion diffusion paths. Specifically, the dry-processed\nelectrode's 5 times greater thickness inherently elevates its absolute impedance, even assuming\nidentical intrinsic conductivity.\nCritically, our study does not claim superior rate capability for dry-processed electrodes -\nindeed, rate test data (Fig. 4c and Supplementary Fig. 18) confirms their lower capacity\nretention at 1 C (48.17 mAh g-1 vs. 84.82 mAh g-1 for wet-processed electrodes) due to mass\ntransport limitations. This manuscript highlights processed’s critical role in overcoming\ncomplete additive decomposition limitations specific to pre-sodiation application, where\nabsolute impedance comparisons across different electrode constructing method are less\nmeaningful.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the discussion on absolute impedance in revised\nmain text (on page 15):\" For comparison between SC and DP electrodes, the higher absolute\nimpedance in DP electrodes versus SC counterparts is primarily attributable to differences in\nelectrode thickness. Specifically, the DP electrode's 5 times greater thickness inherently\nelevates its absolute impedance, even assuming identical intrinsic conductivity. Hence, absolute\nimpedance comparisons across different electrode constructing method are less meaningful, and\nthe resistance is compared between electrodes manufactured by the same procedure.\"\n“Larger R is also observed in SC electrodes after pre-sodiantion than SC electrodes without\nCT\npre-sodiantion, causing larger internal polarization. In contrast, DP electrodes after pre-\nsodiantion show a reduced R from 118.1 to 107.1 Ohm of DP electrodes without pre-sodiation,\nCT\nwhich proves the fast kinetics obtained by Na C O decomposition, contributing to larger\n2 2 4\ncapacities under high current densities.”\nThank you for your constructive feedback throughout the entire review process, which has\nsignificantly strengthened our manuscript.\nReviewer #2 (Remarks to the Author):\nThe manuscript addresses the challenge of low initial Coulombic efficiency in hard carbon\nanodes, a significant obstacle in advancing sodium-ion battery technology. By introducing pre-\nsodiation via sacrificial salts, the authors present a promising approach to overcome this\nlimitation. While conventional slurry casting methods restrict salt utilization, this study\neffectively demonstrates that dry-process electrode fabrication significantly improves electrical\ncontact, enabling nearly theoretical decomposition capacities for Na₂C₂O₄. This strategy is\nlogically sound and technically convincing, representing a meaningful advancement in\ndeveloping high-performance sodium-ion batteries. Overall, the manuscript is well-written but\nrequires some revisions. Detailed comments are provided below.\nAuthors’ response:\nWe appreciate your positive feedback on our research. In this work, we attempt to\ndemonstrate at the fundamental level how high-utilization-ratio of sacrificial salts in high-mass-\nloading cathode can be sustainable obtained by integrating dry-processing and pre-sodiation.\nWe discover that shear-force, compression-force and thermal effect of dry-processing promotes\nformation of homogenous mixture of sodium oxalate (Na C O ) with conductive agents,\n2 2 4\ncontributing to intimate electronic migration pathways for complete Na C O decomposition.\n2 2 4\nImportantly, we thank your constructive comments on improve the quality of our manuscript\nand apologize for unclear presentation and discussion of the data in original manuscript. In\nresponse to your suggestions, we have implemented the following revisions.\n1. The authors argue that salt aggregation occurs more readily in the slurry casting (SC) process.\nHowever, clear evidence supporting this claim is lacking. Typically, poor dispersion is\nconsidered a drawback of dry processes rather than SC methods. Could the authors clarify why\ndispersion is limited in the SC process? Is it related to increased surface area from reduced\nparticle size or due to unfavorable interactions between the salt and the solvent? Additional\ndiscussion and a mechanistic explanation would strengthen this point.\nAuthors’ response:\nWe appreciate the reviewer's request for clarification and have expanded our discussion with\nmechanistic insights.\nThe dispersion limitations in slurry casting (SC) arise from two sequential effects: slurry-\ndispersion challenge and drying-induced redistribution. The particle size of the sacrificial salts\nis reduced to ~2 μm for increasing the capacity utilization ratio and reducing the decomposition\npotential. This increases specific surface area exponentially, demanding higher solvent volumes\nfor effective dispersion. In our work, low solid content of 40% was applied in SC electrodes by\nadding NMP to prepare homogenous slurry with well fluidity for coating. However, even with\ninitially homogeneous slurries, solvent evaporation triggers capillary pressure at the liquid-air\ninterface, as illustrated in Figure R2.1. During solvent evaporation, active particles, conductive\nagents and salts are subjected to a compressive force resulting from capillary pressure, which\ncause crack formation and material inhomogeneity [1-2].\nFigure R2.2 shows sectional morphology of slurry-coated electrodes after solvent drying,\nwhich provides evidence supporting the mechanistic explanation. The NVP particles in the\nslurry-coated electrode are loosely packed with abundant pores, and the conductive agent is\nunevenly distributed and enriched on the electrode surface, which causes cracks and material\ninhomogeneity, as illustrated in Figure R2.1e. Moreover, Na C O aggregation could be clearly\n2 2 4\nobserved, as shown in Figure R2.2b. The uneven and separated distribution between Na C O\n2 2 4\n(yellow) and conductive agents (red) results in the failure to construct an effective electronic\nconductive pathway, causing limited Na C O decomposition in slurry-coated electrode.\n2 2 4\nFigure R2.1. Illustration of the drying process: (a) slurry cast on Al foil; (b) liquid menisci\nformed as water evaporation; (c) crack initiation by the in-plane pressure; (d) crack propagation\nthrough the coating [1]. (e) illustration of material inhomogeneity in slurry-coating electrode [2].\nFigure R2.2. Sectional morphology of slurry-coating electrode calendared under different\npressure. a-b, Electrode without calendaring.\nReference:\n[1] Enabling aqueous processing for crack-free thick electrodes. Journal of Power Sources,\n2017, 354: 200-206.\n[2] Redox-homogeneous, gel electrolyte-embedded high-mass-loading cathodes for high-\nenergy lithium metal batteries. Nature communications, 2022, 13(1): 2541.\nRevisions made to the manuscript:\nIn the revised manuscript, we added mechanistic explanation on the uneven distribution of\nNa C O in slurry-coated electrodes, and added the Figure R2.2 in revised Supplementary\n2 2 4\nInformation as Supplementary Figure 6a-b.\nMain text (on page 11):” The dispersion limitations in slurry casting (SC) arise from two\nsequential effects: slurry-dispersion challenge and drying-induced redistribution. High surface\narea of Na C O particles necessitates excess solvent (NMP) to stabilize the dispersion - yet\n2 2 4\nduring drying, solvent evaporation generates capillary forces that cause crack formation and\nmaterial inhomogeneity 40,41. Supplementary Fig. 6a-b shows sectional morphology of slurry-\ncoated electrodes after solvent drying, which provides evidence supporting the uneven and\nseparated distribution between Na C O and conductive agents.”\n2 2 4\nReference:\n40. Du, Z. et al. Enabling aqueous processing for crack-free thick electrodes. Journal of\nPower Sources 354, 200-206 (2017).\n41. Kim, J.-H., Kim, J.-M., Cho, S.-K., Kim, N.-Y. & Lee, S.-Y. Redox-homogeneous,\ngel electrolyte-embedded high-mass-loading cathodes for high-energy lithium metal\nbatteries. Nature Communications 13, 2541 (2022).\n2. The manuscript states that the salt exhibits a low Young’s modulus (~70 MPa) above 100°C,\nwhich promotes deformation and thus improves dispersion. However, the connection between\nthis mechanical property and improved dispersion remains unclear. Reference 40, cited in the\nmanuscript, discusses enhanced contact between solid electrolytes and cathode materials due to\nparticle deformation. The authors should clarify how salt deformability specifically influences\ndispersion within the context of their study.\nAuthors’ response:\nThanks for your valuable comments. We are sorry for the unclear presentation of the\nconnection between improved Na\n4\ndispersion and the salt deformability. To address the\nreviewer’s concerns, we have now added optical and SEM images of the material powder before\nand after dry-processing, in order to illustrate the enhanced dispersion of Na C O in electrodes\n2 2 4\nby dry-processing method. Figure R2.3 shows that the added white Na C O powder\n2 2 4\ndisappears after high-speed dry mixing. The mixed powder appears uniformly gray, indicating\nthat the Na C O and electrode materials are mixed evenly. Figure R2.4 shows the morphology\n2 2 4\nof Na C O and active materials before and after dry-processing. Na C O particles exhibit\n2 2 4 2 2 4\nrougher surface and decreased particle size (from ~2 μm in origin state to ~1 μm after dry-\nprocessing) than original state, confirming deformation. Different from Na C O aggregation\n2 2 4\ninside slurry-coated electrodes in Figure R2.2, the bright white Na C O particles (due to poor\n2 2 4\nelectronic conductivity) are evenly distributed on the surface of NVP particles after high-speed\ndry mixing. Moreover, the deformed Na C O particles were also inserted into the interior of\n2 2 4\nthe aggregated VGCF, which improves the dispersity of Na C O in VGCF. Importantly, the\n2 2 4\nhigh roller pressure and heat during hot-calendaring at 120 °C further promote Na C O\n2 2 4\ndeformation and compress the mixture to form interlocked structure of VGCF and Na C O .\n2 2 4\nAs\nshown in Figure R2.5. there is no polyhedron-shaped Na C O particle, while obvious Na\n2 2 4\nsignals are observed distributed in the gap between NVP particles. This Na signal is highly\nconsistent with the C signal, indicating that DP method produces a homogeneous mixture\nconsisting of conductive carbon and Na C O , thus establishing an intimate and permanent\n2 2 4\nelectrical contact. Therefore, the salt deformability by DP method enhanced dispersion by\npromoting evenly Na C O distribution on surface of NVP particles and inside interior of VGCF\n2 2 4\nas well as producing compact mixture of VGCF and Na C O .\n2 2 4\nFigure R2.3. Images of powder before and after dry-mixing at a speed of 18000 rpm. The white\npowder is the ball-milled Na C O .\n2 2 4\nFigure R2.4. Effect of dry-mixing on dispersion and deformation of Na C O . a-b, Morphology\n2 2 4\nof the original ball-milled Na C O . c, Morphology of the NVP particles. d-i, Morphology of\n2 2 4\nNVP, VGCF and Na C O powder after dry-mixing at a speed of 18000 rpm.\n2 2 4\nFigure R2.5. Morphology and EDX mapping of section structure of DP electrodes. The scale\nbar is 5 μm in Fig. R2.5b (Fig.3i-j in main text)\nRevisions made to the manuscript:\nIn the revised manuscript, we added discussion on connection between improved Na\n4\ndispersion and the salt deformability, and added the Figure R2.3-2.4 in revised Supplementary\nInformation as Supplementary Figure 10-11.\nMain text (on page 12):” Optical and SEM images of the material powder before and after\ndry-processing were compared in Supplementary Fig. 10-11, in order to illustrate the enhanced\nNa C O dispersion in electrodes by salt deformability. The mixed powder appears uniformly\n2 2 4\ngray, indicating that the Na C O and electrode materials are mixed evenly. After high-speed\n2 2 4\ndry-mixing, Na C O particles exhibit rougher surface and decreased particle size (from ~2 μm\n2 2 4\nto ~1 μm) than original state, confirming deformation. Different from Na C O aggregation\n2 2 4\ninside slurry-coated electrodes in Supplementary Fig. 6, the bright white Na C O particles\n2 2 4\nare evenly distributed on the surface of NVP particles. Moreover, the deformed Na C O\n2 2 4\nparticles were also inserted into the interior of the aggregated VGCF, which improves the\ndispersity of Na C O in VGCF. Importantly, the high roller pressure and heat during hot-\n2 2 4\ncalendaring at 120 °C further promote Na C O deformation and compress the mixture to form\n2 2 4\ninterlocked structure of VGCF and Na C O , which appeared as a mixture of C-Na element\n2 2 4\ndistribution without the observed polygonal morphology of Na C O (Fig. 3i).”\n2 2 4\n3. If the primary issue with the SC process is the formation of a loosely stacked structure, could\nincreasing calendaring pressure beyond the ~10 MPa used in this study further enhance particle\ncontact? Clarifying whether this pressure selection was based on previous studies, experimental\nlimitations, or material-specific considerations would be beneficial.\nAuthors’ response:\nWe thank the reviewer for this insightful question. The selection of 10 MPa calendaring\npressure was based on universal protocols (e.g., Nat Commun 13, 2541 (2022)) and material-\nspecific considerations: higher pressures cause wrinkles in the current collector and the risk of\nseparation of the active material from the current collector. To explicitly test the effect of\ncalendaring pressure on salt decomposition in slurry-coating electrodes, we performed\nadditional experiments at 50 MPa (Figure R2.6). The slurry-coating electrodes exhibit loose\nstacking structure after drying in Figure R2.6a. The Na C O particles showed an aggregated\n2 2 4\ndistribution, which may be due to liquid tension during the solvent drying process. The\nelectrodes were calendared at pressures of 10 and 50 MPa, which was measured by using\npressure sensitive paper in Figure R2.6c-d. The electrode thickness was reduced to 84 and 67\nμm from 109 μm, as shown in Figure R2.6e, i. A more compact stack structure was observed\nin the calendared electrodes, which establish close contact between Na C O particles and\n2 2 4\nconductive agents, as shown in Figure R2.6f, j. However, even under elevated pressure,\naggregated Na C O domains persist, which fracture into isolated fragments, losing electrical\n2 2 4\ncontact with conductive networks (red arrows in Figure R2.6h, l). Similar compensated\ncapacity obtained from potential curves further verified increasing calendaring pressure could\nnot further enhance the Na C O decomposition, as showing in Figure R2.7 and Table R2.1.\n2 2 4\nTherefore, the limited Na C O decomposition in slurry-coated electrodes is due to the Na C O\n2 2 4 2 2 4\naggregation and fragile electrical contact, as analyzed in Question 1# and Figure R2.2.\nFigure R2.6. Sectional morphology of slurry-coating electrode calendared under different\npressure. a-b, Electrode without calendaring. c-d, Images of pressure sensitive paper to show\nthe calendaring pressure. e-f, Sectional morphology of slurry-coating electrode calendared\nunder 10 MPa. g-h, Sectional morphology of slurry-coating electrode calendared under 10 MPa\nafter charging to 4.5 V. i-j, Sectional morphology of slurry-coating electrode calendared\nunder 50 MPa. k-l, Sectional morphology of slurry-coating electrode calendared under 50 MPa\nafter charging to 4.5 V. Na C O is highlighted in yellow, and conductive materials are highlighted\n2 2 4\nin red.\nFigure R2.7. Effect of calendaring pressure on the Na C O decomposition in slurry-coating\n2 2 4\nelectrodes. a-b, Potential curves in initial three cycles for slurry-coating electrodes calendared\nunder 10 MPa. c-d, Potential curves in initial three cycles for slurry-coating electrodes\ncalendared under 50 MPa.\nTable R2.1. Mass change and pre-sodiation capacity of slurry-coating electrodes with adding\n10% Na C O in initial cycle\n2 2 4\nNa C O NVP mass\n2 2 4\norigin Na C O 4.5 V decrease decomposition\n2 2 4\nspecific loading\n/ mg mass / mg mass / mg mass / mg ratio / %\ncapacity / mg cm-2\n0# 17.17 1.03 14.70 0.64 62.00 248.00 10.3\n1# 16.76 1.00 14.34 0.62 62.26 249.05 8.81\n2# 16.88 1.01 14.46 0.61 60.65 242.62 8.90\n3# 16.71 0.99 14.30 0.62 62.52 250.09 8.78\n4# 17.30 1.04 14.82 0.64 61.52 246.07 9.21\n1# and 2# were calendared under 10 MPa, 3# and 4# were calendared under 50 MPa.\nRevisions made to the manuscript:\nIn the revised manuscript, we added discussion on, and added the Figure R2.5-2.6 in revised\nSupplementary Information as Supplementary Figure 6 and 12. The corresponding data table\n(Table R2.1) has been added in the revised Supplementary Information as Supplementary\nTable 4.\nMain text (on page 11):” Even under elevated calendaring pressure of ~50 MPa, aggregated\nNa C O domains persist, which fracture into isolated fragments, losing electrical contact with\n2 2 4\nconductive networks (red arrows in Supplementary Fig. 6h, l).”\nMain text (on page 13):” Same incomplete Na C O decomposition was observed in SC\n2 2 4\nelectrodes calendared under 50 MPa, which show limited decomposition capacity of 250.1 mAh\ng-1, as shown in Supplementary Fig. 12.”\n4. The manuscript reports that the dry-process electrode (DP) exhibits a charge-transfer\nresistance (RCT) over 10 times greater than the SC electrode. A mechanistic explanation for\nthis substantial difference would greatly enhance the manuscript's clarity.\nAuthors’ response:\nWe thank the reviewer for this insightful observation. The higher absolute impedance in dry-\nprocessed electrodes (410 μm thickness, ~5.5 mAh cm-2 areal capacity) versus wet-processed\ncounterparts (84 μm, ~1.1 mAh cm-2) is primarily attributable to differences in electrode\nthickness. According to electrochemical theory, total impedance scales proportionally with\nelectrode thickness due to elongated ion diffusion paths. Specifically, the dry-processed\nelectrode's 5 times greater thickness inherently elevates its absolute impedance, even assuming\nidentical intrinsic conductivity. Critically, dry-processed electrodes exhibit poorer rate\ncapability than slurry-coated electrodes. The rate test data (Fig. 4c and Supplementary Fig. 18)\nconfirms their lower capacity retention at 1 C (48.17 mAh g-1 vs. 84.82 mAh g-1 for wet-\nprocessed electrodes) due to mass transport limitations. And the potential profiles confirm\nlarger overpotential of dry-processed electrodes than slurry-coated electrodes under same\ncurrent density. Hence, absolute impedance comparisons across different electrode constructing\nmethod are less meaningful, and the resistance is compared between electrodes manufactured\nby the same procedure.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added the discussion on absolute impedance in revised\nmain text (on page 15):\" For comparison between SC and DP electrodes, the higher absolute\nimpedance in DP electrodes versus SC counterparts is primarily attributable to differences in\nelectrode thickness. Specifically, the DP electrode's 5 times greater thickness inherently\nelevates its absolute impedance, even assuming identical intrinsic conductivity. Hence, absolute\nimpedance comparisons across different electrode constructing method are less meaningful, and\nthe resistance is compared between electrodes manufactured by the same procedure. \"\n“Larger R is also observed in SC electrodes after pre-sodiantion than SC electrodes without\nCT\npre-sodiantion, causing larger internal polarization. In contrast, DP electrodes after pre-\nsodiantion show a reduced R from 118.1 to 107.1 Ohm of DP electrodes without pre-sodiation,\nCT\nwhich proves the fast kinetics obtained by Na C O decomposition, contributing to larger\n2 2 4\ncapacities under high current densities.”\n5. A critical consideration in thick electrode design is achieving uniform utilization of active\nmaterial from the current collector side to the electrolyte-facing side. Effective electrolyte\ninfiltration is essential to reduce polarization and ensure balanced reaction kinetics throughout\nelectrode thickness. While the authors employed 2D modeling to compare behaviors at 0.1C,\nunder higher current densities, electrolyte concentration gradients between electrode sides\nmight intensify. Have the authors investigated how varying sacrificial salt content affects\nporosity and electrolyte concentration distribution? Further elaboration on why the electrolyte\ncontent was fixed at 10 wt% would be beneficial, particularly regarding whether this value\nwas optimized and how adjusting electrolyte content might impact infiltration and overall\nperformance.\nAuthors’ response:\nWe appreciate the reviewer's insightful suggestion regarding electrolyte distribution in thick\nelectrodes. We added additional data and discussion based on the reviewer’s comments.\n(1) Additional data and discussion on 2D modeling of electrodes sodiated at 0.5 C\nFigure R2.8 shows the variation of electrolyte concentration in the pores and state of\nsodiation of DP electrodes during sodiation at 0.5 C. The re-constructed geometry was same as\nthat of DP electrodes during sodiation at 0.1 C in Fig. 5j-n, and the electrochemical properties\nwas set based on rate test results at 0.5 C in Fig. 4c and Supplementary Fig. 17. Since the\ndifference between the cross-section model and the actual structure limits the convergence of\nthe fit, the simulation time was set to 1200 s. This data can also clearly reflect the relevant\nconclusions. As applying higher current of 0.5 C, the electrodes with/without pre-sodiation\nshow a significant drop in the average electrolyte concentration, due to quick consumption of\nthe Na-ions in the electrolyte storaged in pores. Specifically, DP electrode without pre-sodiation\nonly shows an average electrolyte concentration of 0.15 mol L-1 at 1200 s, which exhibits blue\ncolor in pores near current collector. In contrast, DP electrode after pre-sodiation shows average\nelectrolyte concentration of 0.90 mol L-1 at 1200 s, which maintains red color of electrolyte\nconcentration throughout the electrode thickness, verifying the enhanced electrolyte infiltration\ndue to enlarged pore structure. Consequently, DP electrode with pre-sodiation achieves 7.5%\nhigher average sodium concentration in NVP particles than that of DP electrodes without pre-\nsodiation.\nFigure R2.8. 2D modeling results in terms of electrolyte concentration and state of sodiation\nfor DP electrodes without pre-sodiation (a, d) and with pre-sodiation (b,e). The bottom of\nelectrodes is the location of current collector, and the top is the separator. c, The simulated\naverage electrolyte concentration in DP electrodes during sodiation under current density of 0.5\nC. f, The simulated average sodium concentration in DP electrodes during sodiation under\ncurrent density of 0.5 C.\n(2) Additional data and discussion on dry-processing NVP electrodes with adding 20 wt%\nNa C O\n2 2 4\nThe original manuscript of Na C O content was fixed at 10% for two reasons. One is that\n2 2 4\nthis is the general addition amount of sacrificial sodium additives in published articles (Adv.\nMater. 2020, 32, 2001419, Adv. Mater. 2024, 2407720). Another is that the supplementary\ncapacity of adding 10 wt% Na C O equals the irreversible capacity of all-dry-processing NVP\n2 2 4\n|| HC SIB using ester electrolyte in this work, which was ~2.5 mAh cm-2 for ~52 mg cm-2 NVP\nelectrode.\nThe performance of DP electrodes containing 20 wt% Na C O was further evaluated by\n2 2 4\nanalyzing decomposition capacity, electrode mass change and elemental distribution in Figure\nR2.9-2.11. Specifically, DP electrodes with 20 wt% Na C O maintain effective pre-sodiation\n2 2 4\nwith a high decomposition capacity of 390.88-394.28 mAh g-1 based on the mass of Na C O\n2 2 4\n(Table R2.2), corresponding to decomposition ratio of 96.49% - 98.57% and a supplementary\ncapacity of ~4.2 mAh cm-2. Figure R2.10 shows that the porosity of DP electrodes containing\n20 wt% Na C O was effectively increased after Na C O decomposition, where the gap\n2 2 4 2 2 4\nbetween NVP particles reached ~2 μm from compact structure in original state. The Na C O\n2 2 4\ndecomposition was further verified by the Na elemental distribution on Ar+-polished cross\nsection. Three positions on different thickness of electrode were chosen, as shown in Figure\nR2.11. Similarly, consistent distribution of Na and C signal in original state confirm the intimate\ncontact between Na C O and VGCF. And, the Na signal comes only from NVP in DP\n2 2 4\nelectrodes charged to 4.5 V, verifying the high proportional decomposition of Na C O .\n2 2 4\nFigure R2.9. Potential curves of dry-processing NVP electrodes with adding 20 wt% Na C O\n2 2 4\nto show repeatability.\nTable R2.2. Mass change and pre-sodiation capacity of dry-processing electrodes with adding\n20% Na C O in initial cycle\n2 2 4\nNa C O NVP mass\n2 2 4\norigin Na C O 4.5 V decrease decomposition\n2 2 4\nspecific loading\n/ mg mass / mg mass / mg mass / mg ratio / %\ncapacity / mg cm-2\n1# 70.94 11.82 59.29 11.65 98.57 394.28 47.08\n2# 71.55 11.93 59.90 11.65 97.72 390.88 47.49\n3# 76.36 12.73 64.08 12.28 96.49 385.96 50.68\n4# 70.37 11.73 58.82 11.55 98.50 394.00 46.71\nFigure R2.10. Sectional structures of dry-processing NVP electrodes with adding 20 wt%\nNa C O before and after pre-sodiation. a-c, Electrode before pre-sodiation. d-f, Electrode with\n2 2 4\npre-sodiation.\nFigure R2.11. Ion-milled sectional structures of dry-processing NVP electrodes with adding 20\nwt% Na C O before and after pre-sodiation. a-d, Morphology and EDX mapping of section\n2 2 4\nstructure of electrodes before pre-sodiation, which are V, P, Na, O, C and F element distribution,\nrespectively. e-h, Morphology and EDX mapping of section structure of electrodes after pre-\nsodiation, which are V, P, Na, O, C and F element distribution, respectively. i-j, Sectional\nstructure and pores of DP electrodes before pre-sodiation. k-l, Sectional structure and pores of\nDP electrodes after pre-sodiation.\nHowever, the DP electrodes with 20 wt% Na C O show larger overpotentials of ~15.1 mV\n2 2 4\n(Figure R2.9) than those of DP electrodes with 10 wt% Na C O (~8.4 mV, Figure R2.12).\n2 2 4\nMoreover, DP electrode with adding 20 wt% Na C O exhibits poorer rate capability after pre-\n2 2 4\nsodiation compare to that of DP electrodes with adding 10 wt% Na C O . Specifically, as shown\n2 2 4\nin Figure R2.13a-b, the specific capacities were 95.77, 84.17, 79.08 and 57.27 mAh g-1 at\ncurrent densities of 0.1, 0.3, 0.5 and 1C, respectively. These results indicate sluggish reaction\nkinetics of DP electrodes with adding 20 wt% Na C O , which was further evaluated using EIS\n2 2 4\ntest on symmetric cell. DP electrodes with adding 20wt% Na C O obtains lower ionic\n2 2 4\nresistance than that of the DP electrodes without pre-sodiation, attributing to the enlarged pore\nsize by Na C O decomposition. However, DP electrodes with adding 20wt% Na C O\n2 2 4 2 2 4\nexhibited both larger charge transfer resistance (137.5 Ohm) and ionic resistance (423.5 Ohm)\nter pre-sodiation than those of DP electrodes with adding 10wt% Na C O (107.1 and 372.2\n2 2 4\nOhm). The enlarged resistance might due to the excessive gap spacing (Figure R2.10), which\ncauses loose contact between VGCF and electrode material, affecting the electron transfer.\nThese results confirm the dry-processing method could still promotes high proportional\ndecomposition of Na C O , while the electrochemical performance is limited by the increased\n2 2 4\ncharge transfer resistance. The dry-processing electrode containing high Na C O content could\n2 2 4\nbe optimized by tailoring the electronic conductive network, which is beyond the scope of this\nwork and will be studied in the future.\nFigure R2.12. Potential curves of dry-processing NVP electrodes with adding 10 wt% Na C O\n2 2 4\nto show repeatability.\nFigure R2.13. Rate capability of dry-processing NVP electrodes with adding 20 wt% Na C O ,\n2 2 4\nwhich was charged to 4.5 V in initial cycle. a, Rate performance. b, Potential curves at different\ncurrent densities. c-d, EIS results from symmetric cells tests and corresponding resistances.\nRevisions made to the manuscript:\nIn the revised manuscript, we have added Figure R2.9 in revised Supplementary Information\nas Supplementary Figure 28 and added the discussion in revised main text (on page 18):\"\nUnder higher current density of 0.5 C (Supplementary Fig. 28), electrolyte concentration\ngradients between electrode sides intensify for DP electrodes without pre-sodiation; while DP\nelectrode after pre-sodiation maintains high average electrolyte concentration of ~0.90 mol L-\n1, which shows red distribution throughout electrode thickness.\"\nAnd we have added the Figure R2.9-2.11, 2.13 and Table R2.2 in revised Supplementary\nInformation as Supplementary Figure 14-16, 19 and Supplementary Table 6. The\ncorresponding discussion have been added in the revised main text (on page 13):” The\nperformance of DP electrodes containing 20 wt% Na C O was further evaluated by analyzing\n2 2 4\ndecomposition capacity, electrode mass change and elemental distribution in Supplementary\nFig. 14-16. Specifically, DP electrodes with 20 wt% Na C O maintain effective pre-sodiation\n2 2 4\nwith a high decomposition capacity of 394.28 mAh g-1 based on the mass of Na C O\n2 2 4\n(Supplementary Table 6).”\n6. In the SC process, VGCF and Super P were used as conductive additives, whereas only VGCF\nwas employed in the DP. Given VGCF’s known role in forming electron-conductive networks,\ncould this have enhanced Na₂C₂O₄ decomposition in the DP? If so, can the observed differences\nbe solely attributed to processing methods, or do conductive additive choices also contribute?\nClarification on whether VGCF disperses poorly in the SC process would be helpful.\nAuthors’ response:\nWe appreciate the reviewer’s astute observation and insightful suggestion. The conductive\nadditive selection was driven by process constraints, not performance optimization. While\nVGCF enhances electron transport in both systems, its effectiveness is process-dependent: In\ndry-processing electrode, fibrillar networks provide direct electronic pathways to Na C O\n2 2 4\nparticles, whereas in slurry-coated electrodes, solvent migration during drying disrupts\nconnectivity. The conductive agent is unevenly distributed and enriched on the electrode surface,\nwhich causes cracks and material inhomogeneity, as illustrated in Figure R2.1e [1-2].\nFigure R2.1. Illustration of the drying process: (a) slurry cast on Al foil; (b) liquid menisci\nformed as water evaporation; (c) crack initiation by the in-plane pressure; (d) crack propagation\nthrough the coating [1]. (e) illustration of material inhomogeneity in slurry-coating electrode [2].\nReference:\n[1] Enabling aqueous processing for crack-free thick electrodes. Journal of Power Sources,\n2017, 354: 200-206.\n[2] Redox-homogeneous, gel electrolyte-embedded high-mass-loading cathodes for high-\nenergy lithium metal batteries. Nature communications, 2022, 13(1): 2541.\nFigure R2.14 shows additional sectional morphology of slurry-coated electrodes to confirm\nthis material inhomogeneity. Aggregated VGCFs are dispersed in the electrode cross section\nand concentrated on the surface (Figure R2.14 c-d). In comparison, nanoparticulate Super P\nare more evenly dispersed across the active material surface. Importantly, Na C O lacks close\n2 2 4\ncontact with these conductive agent particles, as shown in Figure R2.14 e-h. Na C O\n2 2 4\naggregates independently and is distributed in pores between NVP particles in slurry-coated\nelectrodes. The resulting weak electrical contact is a key reason for limited Na C O\n2 2 4\ndecomposition in slurry-coated electrodes. The high sacrificial agent utilization in dry-\nprocessing electrode is thus primarily attributable to structural advantages by mechanical and\nthermal effect of dry processing method, not additive selection.\nFigure R2.14. Sectional morphology of slurry-coating electrode calendared under 50 MPa. a-\nb, Overview of the cross-section through the thickness. c-d, Magnified views of VGCF\naggregated on the surface side of the electrodes in a-b. e-f, Magnified view of aggregated\nNa C O in a (green box). g-h, Magnified view of aggregated Na C O in b (blue box). (for\n2 2 4 2 2 4\nreview only, not included in supplementary information).\nRevisions made to the manuscript:\nIn the revised manuscript, we added mechanistic explanation on the uneven distribution of\nNa C O in slurry-coated electrodes,\n2 2 4\nMain text (on page 11):” The dispersion limitations in slurry casting (SC) arise from two\nsequential effects: slurry-dispersion challenge and drying-induced redistribution. High surface\narea of Na C O particles necessitates excess solvent (NMP) to stabilize the dispersion - yet\n2 2 4\nduring drying, solvent evaporation generates capillary forces that cause crack formation and\nmaterial inhomogeneity 40,41. Supplementary Fig. 6a-b shows sectional morphology of slurry-\ncoated electrodes after solvent drying, which provides evidence supporting the uneven and\nseparated distribution between Na C O and conductive agents.”\n2 2 4\nReference:\n40. Du, Z. et al. Enabling aqueous processing for crack-free thick electrodes. Journal of\nPower Sources 354, 200-206 (2017).\n41. Kim, J.-H., Kim, J.-M., Cho, S.-K., Kim, N.-Y. & Lee, S.-Y. Redox-homogeneous,\ngel electrolyte-embedded high-mass-loading cathodes for high-energy lithium metal\nbatteries. Nature Communications 13, 2541 (2022).\n7. In the EIS data (Fig. 4d-f), even after pre-sodiation, DP resistance remains approximately 10\ntimes higher than SC, indicating greater ionic and charge-transfer overpotential. However, Fig.\n4a shows DP voltage hysteresis is initially larger but becomes smaller than SC from the second\ncycle onward. Could the authors clarify this behavior? Additionally, while the manuscript\nmentions “effective electronic pathways” developing in DP, this seems contradictory to the high\nresistance shown by EIS data. A detailed explanation reconciling these findings with the\nproposed electronic pathway formation mechanism would greatly improve clarity.\nAuthors’ response:\nThanks for reviewer's insightful comments. We have added new data to correct these\ndescriptions.\nAs discussed of EIS data in Question 4#, dry-processed electrodes (410 μm thickness, ~5.5\nmAh cm-2 areal capacity) shows higher absolute impedance than slurry-coated counterparts (84\nμm, ~1.1 mAh cm-2) due to differences in electrode thickness. And the potential profiles in rate\ntests confirm larger overpotential of dry-processed electrodes than slurry-coated electrodes\nunder same current density. The original data of slurry-coated electrodes was not correct and\nmight be affected by battery assembly. In revised manuscript, we have added additional test\ndata of multiple independent electrode batches to show the reproducibility. Figure R2.7 shows\nthe repeated tests of slurry-coated electrodes, which all show lower voltage hysteresis of ~ 4\nmV than those of dry-processing electrodes (~8.4 mV). The Figure 4a in main text has been\nrevised using new potential profiles of slurry-coated electrodes, as shown in Figure R2.15.\nFigure R2.7. Effect of calendaring pressure on the Na C O decomposition in slurry-coating\n2 2 4\nelectrodes. a-b, Potential curves in initial three cycles for slurry-coating electrodes calendared\nunder 10 MPa. c-d, Potential curves in initial three cycles for slurry-coating electrodes\ncalendared under 50 MPa.\nFigure R2.15. Potential curves of slurry-coating and dry-processing electrodes during\npresodiation process. The inserted graph compares the decomposition capacities of Na C O ,\n2 2 4\nwhich was calculated based on the decreased electrode mass.\nFurthermore, since less meaningful for comparing absolute impedance comparisons across\ndry-processed and slurry-coated electrodes, the potential profiles were compared between\nelectrodes manufactured by the same procedure. The resistance relationship is consistent with\nthe overpotentials of potential profiles in rate tests Figure R2.16-2.17), where DP electrodes\nafter pre-sodiation show lower overpotential than that of DP electrodes without pre-sodiantion,\nbut SC electrodes after pre-sodiation show higher overpotential. The different results are caused\nby fact that Na C O was completely removed from the DP electrode and generates pores for\n2 2 4\nenhanced electrolytes infiltration, while a certain amount of non-conductive Na C O remained\n2 2 4\nin the SC electrode to hinder the electron transfer.\nFigure R2.16 (Supplementary Fig. 17). Potential curves of dry-processing electrodes with and\nwithout presodiation.\nFigure R2.17 (Supplementary Figure 18). Rate performance and corresponding potential\ncurves of slurry-coated NVP electrodes with and without Na C O .\n2 2 4\nRevisions made to the manuscript:\nIn the revised manuscript, we have revised the discussion on potential profiles and resistance.\nAnd the original Figure 4a has also been revised as Figure R2.12.\nThe original discussion of “effective electronic pathways developing in DP” in Main text has\nbeen deleted:” During second cycle, DP electrode shows lower voltage hysteresis of 0.0933 V\nand larger capacity of 105.2 mAh g-1, comparing to 0.1544 V and 99.77 mAh g-1 for SC\nelectrodes with much lower mass loading, which implies effective electronic pathways in DP\nelectrodes are still maintained after Na C O decomposition.”\n2 2 4\nAdditional discussion on resistance and overpotential have been added in main text (page\n15): “The resistance relationship is consistent with the overpotentials of potential profiles in\nrate tests (Supplementary Fig. 17-18), where DP electrodes after pre-sodiation show lower\noverpotential than that of DP electrodes without pre-sodiantion, but SC electrodes after pre-\nsodiation show higher overpotential.”\n8. In the full-cell configuration (Fig. 6), the authors employed a DP electrode fabrication method\nwith PTFE as the binder for the hard carbon anode. PTFE is known to decompose at potentials\naround 1.5 V vs. Na/Na⁺, causing irreversible capacity loss (DOI: 10.1016/j.joule.2024.01.028).\nThis property is problematic in hard carbon systems already challenged by low initial\ncoulombic efficiency. Although the authors attempted to address this issue via pre-sodiation,\nthe rationale for selecting PTFE as a binder remains unclear. Could the authors clarify why\nPTFE was chosen and why the DP approach utilizing PTFE was preferred, despite its potential\nto exacerbate initial cycle coulombic inefficiency?\nAuthors’ response:\nWe thank the reviewer for raising this critical concern. Our selection of PTFE is justified by\ntwo reasons. 1. PTFE is easy-manufacturing for dry-processing due to its unique fibrillization\nbehavior. 2. Despite low initial coulombic efficiency, hard carbon dry-processing electrodes\nwith PTFE as binder maintain superior cycling stability. As shown in Figure R2.17, 9.6 mg cm-\n2 (2.6 mAh cm-2) dry-processing HC electrode with PTFE as binder retain 89.79% capacity\nafter 2850 cycles under a current density of 1 C. Recently, solving the low ICE is the hot\nresearch topic in dry-processing negative electrode, such as PEO-coating (DOI:\n10.1016/j.joule.2024.01.028). In this work, the novel strategy combining sacrificial salts pre-\nsodiation and dry-processing electrode can effectively compensate for the irreversible capacity\nin the initial cycle, thereby improving the energy density, extending the cycle life, and saving\nthe production cost of large-scale production of SIBs.\nFigure R2.17. Cycleing performance of HC electrode with PTFE as binder, which was tested\nin half cell. (for review only, not included in supplementary information).\nOnce again, we deeply value your constructive and supportive review. Your expertise has\nstrengthened our manuscript.\nReviewer #3 (Remarks to the Author):\nIn this manuscript, Qin et al. offer a robust study combining dry-processing and sacrificial salt\npre-sodiation to fabricate high-performance sodium-ion batteries (SIBs). In a dry-processed\nelectrode architecture, the authors overcome one of the utmost challenges in SIB technology—\nthe limited initial coulombic efficiency and energy density—by using sodium oxalate (Na₂C₂O₄)\nas a pre-sodiation agent.\nThe experimental methods used are exhaustive and solid, such as state-of-the-art electrode\nfabrication through high-speed shear mixing and hot calendaring and extensive morphological,\nstructural, and electrochemical characterization. SEM, XRD, XPS, DSC, AFM, DEMS, and\nEIS techniques are applied proficiently to understand how processing conditions impact the\nelectrode structure, mechanical stability, electronic conductivity, and decomposition behavior\nof Na₂C₂O₄ These polymer modifications are also enhanced by 2D modeling of ion diffusion\nand electrolyte penetration to comprehend structural effects stemming from pre-sodiation.\nThe novelty of our work is that it shows, in the context of electrochemical co-doping based on\nthe well-known Na₂C₂O₄ precursor, how dry-processing avoids the disadvantages associated\nwith slurry-based methods (e.g., poor dispersion, high solvent requirements, particle\nagglomeration), while simultaneously achieving much better utilization of the Na₂C₂O₄ based\non the production of homogeneous, conductive, and physiologically stable electrode scaffolds.\nThe synergy renders a theoretical-level decomposition rate (400 mAh g⁻¹), enhanced porosity\nand ionic transport, and a significant enhancement of energy density (82.5%) and cycling life\n(additional 200 cycles), respectively.\nSignificantly, the authors demonstrate the practicality of their method via roll-to-roll fabrication\nof ultra-thick electrodes and full-cell testing using dry-processed hard carbon anodes and obtain\noutstanding areal capacity (5.4 mAh cm⁻²), high volumetric energy density, and excellent\ncycling stability. These findings set the stage for scalable, sustainable, and high-energy-density\nSIB production.\nI thus recommend the manuscript for publication in Nature Communications.\nAuthors’ response:\nWe are deeply grateful for the reviewer’s thorough evaluation and strong endorsement of our\nwork. We are gratified that the reviewer recognized the key aspects of our work, including\nmethodological rigor, exhaustive and solid characterization as well as practical significance. In\nthis work, we attempt to demonstrate at the fundamental level how high-utilization-ratio of\nsacrificial salts in high-mass-loading cathode can be sustainable obtained by integrating dry-\nprocessing and pre-sodiation. We discover that shear-force, compression-force and thermal\neffect of dry-processing promotes formation of homogenous mixture of sodium oxalate\n(Na C O ) with conductive agents, contributing to intimate electronic migration pathways for\n2 2 4\ncomplete Na\n4\ndecomposition. The mechanism was detailly demonstrated by experimental\ncharacterization and model simulation. The feasibility in practical manufacturing of the\ndesigned electrode is also verified by roll-to-roll production in lab-scale.\nWe thank the reviewer for their encouraging assessment, which affirms our goal to bridge\nfundamental innovation with real-world impact. Their support strengthens our resolve to\nadvance sustainable battery manufacturing. Once again, we deeply value your constructive and\nsupportive review."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised manuscript has addressed the reviewer's comments well. It can be recommended for acceptance.", "reviewer_2": "The authors have addressed and revised all of my concerns. The revised review manuscript is now much clearer. I believe the manuscript should be accepted for publication."}, "author_response": ""}]

Decision letter