Tailored charging protocol for densified lithium deposition and stable initially anode-free lithium metal pouch cells

Domain: chemistry
Published: 2025-12-23
Editorial outcome: minor_revision

Abstract
The low mechanical strength and insufficient lithium-ion conductivity of solid-electrolyte interphase will incur inhomogeneous lithium deposition and eventually cause battery failure, hindering practical application of lithium metal batteries. Combining multiple characterization techniques and COMSOL simulation, here we report that the commonly-adopted constant current charge protocol would result in formation of highly porous lithium metal negative electrode, leading to severe parasitic reactions. To ameliorate this problem, we propose a middle peak current charge protocol with a peak current in the middle of charging step, which could guide the nucleation and growth of densified lithium deposition with the derived solid-electrolyte interphase possessing significantly improved mechanical strength and Li+ ion conductivity. Therefore, coin-type initially anode-free lithium metal batteries could be stably cycled for 80 cycles (with 3 hours of charging and state-of-charge of ~70%). A 1.5 Ah initially anode-free Li metal pouch cell which delivers a specific energy of 400 Wh kg-1 at 225 mA and with a capacity retention of 80% for 298 cycles (with 3 hours of charging and state-of-charge of 80%) is also demonstrated.

Introduction
Lithium (Li)-ion batteries (LIBs) using graphite negative electrode have been widely used for portable electronic devices and automotive applications since their development in 1990s1,2. However, the energy density of existing Li-ion batteries is far below the demands for ever-increasing markets, such as long-term transportation and grid-scale energy storage. Therefore, Li metal batteries (LMBs) with lithium metal negative electrode (LMNE, 3860 mAh g-1) have been reconsidered for future applications3. However, for the high self-diffusion barriers of Li adatoms to form Li nuclei4 and the insufficient Li+ ion conductivities and mechanical strength of the solid electrolyte interphase (SEI) on LMNE5, the dendritic LMNE will be formed during the charge process of LMBs. Their regular surface curvature of LMNE will also boost the formation of Li dendrites, and the high charge current will accelerate this process6. Extensive research on Li metal structure7, compatible electrolyte system8–11, artificial SEI12,13 and current collectors14–18 has been carried out to improve the performance of LMBs. However, until today, the formation of porous Li metal, as well as the plating of dendritic Li, are still inevitable. In addition, it is still challenging to achieve large-scale processing of Li foil because of the sensitivity of lithium towards air humidity19. To this end, the initially anode-free LMBs (IAFLMBs), is highly desirable for the commercialization of LMBs. They are not only compatible with the existing battery infrastructure but also deliver the highest energy density among all the reported structural prototypes of LMBs20,21. However, the volume expansion/contraction of LMNE during charge/discharge of IAFLMBs makes the surficial SEI of LMNE to break easily, particularly under industry-relevant conditions such as high cell capacity, fast charging rate and low stack pressure. This creates gaps in achieving high-performance IAFLMBs with high energy density22 even though a 0.23 Ah IAFLMBs with 80% of its capacity retention after 200 cycles was demonstrated23. Therefore, despite tremendous efforts such as electrolyte engineering10,23–26 and test-pressure adjustment21, developing Ah-level IAFLMBs with stable cycle life and high specific energy remains challenging.

The cycling performance of traditional LIBs can be increased by using many advanced cycling protocols, especially under the fast-charging conditions27–29. For LMBs, the charge/discharge current represents the plating/dissolution rate of LMNE, respectively. It has been reported that the small charging current is helpful in boosting the reversibility of LMNE30,31, the small discharging current of LMBs can boost the void-free Li metal dissolution32, and their relative values will also influence the cycling performances of LMBs33. A prominent study also showed that isolated Li can be reutilized by controlling the discharge protocols of LMBs34,35. Besides, various charge protocols have been proposed to increase the cycling performance of lithium battery, for example, the pulsed current36,37, the asymmetric bidirectional current38, the two-step current39, the self-heat current40, the initially high current seeded Li metal growth41,42 and the simulated non-linear potentiodynamic battery charging protocols43, and so on. Some of them have shown successes in industrial applications, while the underlying role of different charge protocols for LMBs remains poorly understood.

The electrochemical deposition of thin films on the substrates is generally in a “stressed” state, for example, Sn and Cu thin films44,45. This has been shown as a universal phenomenon that exists in thin films deposition46–48. The presence of compressive stress during Li plating process had also been identified, which would promote the growth of Li dendrite49,50. Strategies have been developed to mitigate the stress of LMNE, including 1) utilization of stress-releasing substrate; 2) formation of mechanically strong SEI; and 3) small operating current density. The utilization of soft substrate49 or hemisphere-like concaves51 is helpful in releasing the internal stress of LMNE. The small operating current density cannot only decrease the stress load in LMNE49, but also guide the formation of SEI with increased mechanical strength compared with that formed at large current density52 (Fig. 1a, b). Thus, the Li metal deposited at relatively small current densities holds a uniform and dense structure7,52,53. However, the small charging current strongly limits the fast-charging capability of LMBs.

The internal stress of LMNE is proportional to the deposited stack capacity and current density, which is one of the main constraints to forming a densely packed structure. Meanwhile, the as-deposited Li atoms can also act as nucleation seeds and growth substrate for subsequent Li plating, guiding a more uniform deposition. Bearing such a correlation between internal stress and Li growth rate in mind, we propose a middle peak current (MPC) charge protocol for LMBs (Fig. 1c), with a peak current in the middle of the charging step to regulate Li deposition. With such an MPC protocol, the formed LMNE consists of a densified structure and with the derived SEI possessing high strength and Li ion conductivity, thus an Ah-level IAF Li metal pouch cell with industrial-level loading positive electrodes could retain 80% of its capacity even after 298 cycles.

Results
Methodology, cell performance, and morphology
The key to the MPC protocol is its small starting and ending currents, and peak current in the middle. Therefore, compared with the traditional constant current (CC) plating protocol (1 mA cm-2, Fig. 1d, e), we designed an MPC protocol with its initial and final current densities being 0.5 mA cm-2 and the middle current density being 2 mA cm-2 in Li||Cu cells (Fig. 1g, h). Note that the total plating time for both CC and MPC protocols is the same as 3 h. After the plating process, the deposited Li metal for both the CC and MPC protocols was stripped at 1 mA cm-2. As shown in Fig. 1f, i, the MPC protocol delivers a much higher coulombicefficiencies (CEs) and data consistency than the CC protocol. In addition, the MPC protocol also demonstrates higher average CEs (Supplementary Fig. 1) and better cycling stability at 60 °C (Supplementary Fig. 2a), and higher CEs under an areal capacity of LMNE of 0.3 mAh cm-2 (Supplementary Fig. 2b–d) or 6 mAh cm-2 (Supplementary Fig. 2e–g). The comparison with many other existing charge protocols (Supplementary Figs. 3-4) further validates the effectiveness of the MPC charge protocol in stabilizing LMNE during repeated plating/stripping processes. Varying the position of the largest current density (Fig. 1d, e, g, h and Supplementary Fig. 5), the cell achieved the best performance when it was placed at the third step (Fig. 1f, i and Supplementary Fig. 6), demonstrating the effectiveness of MPC protocol.

The morphologies of deposited Li metal through CC and MPC plating protocols (Supplementary Table 1) in Li||Cu cells were characterized by scanning electron microscopy (SEM). When 0.25 mAh cm-2 of Li metal was deposited at 0.5 mA cm-2 (MPC1 sample, Fig. 2e, f), spherical Li metal morphology was observed, while the Li metal that was deposited at 1 mA cm-2 was less spherical (CC1 sample, Fig. 2a, b). For the CC2 sample, the Li metal deposited through CC protocol exhibits a kind of porous structure (Supplementary Fig. 7). However, the Li metal deposited via MPC protocol always yields a densely packed structure (Supplementary Fig. 8). When the Li capacity increases to 3 mAh cm-2 (theoretical thickness of ~12.9 μm), the Li metal deposited through CC protocol presents a porous “Zone 1” like structure (Fig. 2c) and delivers a thickness of 16.7 μm (Fig. 2d), which corresponds to a porosity of 22.9% and should be avoided for dense film growth54. Conversely, for the Li metal film at the same capacity of 3 mAh cm-2, the MPC protocol results in a denser “Zone 3” like structure (Fig. 2g) with a thickness of only 13.6 μm (Fig. 2h), which corresponds to a porosity of 5.4% only. As shown in Supplementary Fig. 9, the thickness of deposited Li through the MPC protocol is obviously smaller than the porous and loose Li metal structure formed by many other protocols (≥14 μm, with porosity ≥8.1%). The densified lithium could thus suppress the parasitic reactions with the electrolytes, leading to the formation of a thinner by-products layer (induced by the side-reactions between Li metal and electrolyte) than those by many other protocols after repeated cycling tests (Fig. 2j and Supplementary Fig. 9).

Apart from the deposition process of LMNE with relatively higher stack pressure in coin-type cells, Li deposition under smaller stack pressure is also important for practical application51. Therefore, a hollow PTFE spacer is added to characterize the Li metal morphologies at relatively ample space (Supplementary Fig. 10). Li grown through CC protocol shows a severe lumped structure regardless of the spacer thickness (200 or 300 μm). By contrast, Li metal formed through the MPC protocol tends to distribute uniformly. The lumped Li metal structure results from the centralized interaction between perpendicular dendrite growth and the pressure from the separator, which is undesirable for cell operation.

Mechanical strength, transport properties and compositions of SEI
Atomic force microscopy (AFM) was employed to characterize the microstructures and mechanical properties of the derived SEI by CC and MPC protocols. To minimize the random errors of modulus test that may be caused by the position variations of electrodes, we conducted the modulus tests at three positions of LMNE, as shown in Supplementary Fig. 11a. When we choose the test results at position 2 (i.e., the central area of the electrode) of different samples to make a comparison, the Young’s modulus of the initial SEI (with Li capacity of 0.25 mAh cm-2) at 1 mA cm-2 for CC1 (1.1 GPa, Fig. 2l) is lower than that formed at 0.5 mA cm-2 for MPC1 (2.1 GPa, Fig. 2n). This shows that the SEI formed at smaller current density would possess a higher modulus. Moreover, when Li metal was deposited at 3 mAh cm-2, the Young’s modulus of the derived SEI via MPC protocol (MPC6 (5.3 GPa), Fig. 2o) is 89% higher than that formed by CC protocol (CC6 (2.8 GPa), Fig. 2m). Although the modulus of SEI will change with the positions where it is measured, the averaged values of MPC1 sample (2.3 GPa) and MPC6 sample (4.9 GPa) are respectively 130 and 96% higher than those of CC1 sample (1 GPa) and CC6 sample (2.5 GPa), demonstrating the advantage of MPC protocol in forming SEI with a high mechanical strength (Supplementary Fig. 11b and Supplementary Fig. 12). When the plated Li metal was fully stripped, the tested modulus of MPC1 sample is also higher than that of CC1 sample (Supplementary Fig. 13), aligns well with the above modulus analysis. The Young’s modulus of the as-formed SEI on Li metal through MPC protocol is also much higher than that of SEI formed by other protocols (≤4 GPa, Fig. 2k and Supplementary Fig. 14). The Peak Force TUNA test of AFM characterizations was conducted to show the contact current of CC1, MPC1, CC6 and MPC6 samples, respectively, as shown in Supplementary Fig. 15. The results clearly show that the SEI formed on MPC1 sample has smaller electrical conductivity than that of CC1 sample, which means that the SEI formed at a small current density (0.5 mA cm-2, MPC1 sample) has better electrical insulation properties than the SEI formed at a large current density (1 mA cm-2, CC1 sample). Even after 3 mAh cm-2 of Li metal was deposited, the SEI on CC6 sample still delivers a higher electrical conductivity compared to that of the SEI formed on MPC6 sample. The above AFM characterization results clearly show that the MPC protocol can enable the formation of SEI with high modulus and low electrical conductivity, suppressing the formation of porous LMNE.

Apart from modulus, the lithium-ion diffusivity through the SEI also depends on the microstructures of deposited lithium. Temperature-varying electrochemical impedance spectrum (EIS) tests between -20 °C and 30 °C were carried out. The linear fitting between the natural logarithm of resistance and the reciprocal of temperature, namely Arrhenius relation (ln R = Ea/RT + C, C is a constant), can give the value of activation energy (Ea) for a specific process. Typically, the semi-circle of RSEI in the high (105 Hz)-middle (103 Hz) range arises from the impedance of the interfacial film on Li metal, while the semi-circle of RDe in the low frequency range (103 Hz to 100 Hz) reflects the charge-transfer process (Supplementary Fig. 16a). Therefore, the activation energies Ea,SEI and Ea,De, which were obtained by fitting the obtained RSEI and RDe via Arrhenius relation, representing the transport process of Li+ ions in SEI film and the de-solvation process of Li+ ions, respectively55. As shown in Supplementary Fig. 16b–m, for the SEI formed on CC1 sample, the solvated Li+ ions would be de-solvated (Ea,De = 38.6 kJ mol-1) more easily compared to that of MPC1 sample (Ea,De = 42.8 kJ mol-1), while the transportation of Li+ ions through both SEIs are almost the same (Ea,SEI = 65 kJ mol-1 of CC1 sample compared to 65.8 kJ mol-1 of MPC1 sample). However, for the SEI formed on the MPC6 sample, both the desolvation (36.4 kJ mol-1) and transport of Li+ ions (59 kJ mol-1) are easier than those of the CC6 sample (38.5 kJ mol-1 for desolvation and 65.9 kJ mol-1 for transport of Li+ ions, respectively). In addition, both the SEI diffusivity (DS) and bulk diffusivity (DB) of Li ions are important for Li metal morphology56. Therefore, these two values are further examined (Supplementary note and Supplementary Table 2). It was found that the DS/DB values for both the CC1 and MPC1 samples are almost the same, while the final SEI formed via MPC protocol delivers a much higher DS/DB value, which further ascertains the more favorable Li-ion transportations for the SEI formed by the MPC protocol.

X-ray photoelectron spectroscopy (XPS) depth-profiling analysis was further carried out to characterize the composition of SEI formed at different stages of CC and MPC protocols (Supplementary Figs. 17–23). As shown in Supplementary Fig. 17, there is an obvious increase in the carbon signal of CC3 sample compared with that of CC2 sample, and this may result from the increased side reactions between the formed porous Li metal (Supplementary Fig. 7) and electrolyte. As shown in Supplementary Fig. 18, although there is still an increase in carbon signal at the inner SEI of MPC3 sample compared to that of MPC2 sample and which may result from the high middle current accelerated solvent decomposition, the carbon signal for the SEI of MPC plated Li metal remains stable. For the O 1s spectra, there are more contents of C=O in CC plated Li metal (Supplementary Fig. 19) compared to that of MPC plated Li metal (Supplementary Fig. 20). For the F 1s XPS depth profiles, the SEI formed on CC1 sample is rich in surficial LiF content (Supplementary Fig. 21), differing from the inner LiF-rich while low LiF content structure of MPC1 sample (Supplementary Fig. 22). Apart from the modulus of SEI, the difference in LiF content between CC1 and MPC1 samples may also be the reason for the formation of porous Li metal structure of CC2 sample as shown in Supplementary Fig. 7b. The SEI formed by CC current has a high LiF content on its surface (Supplementary Fig. 21f), which is less favorable for Li-ion transportation because the Li-ion conductivity through LiF is very low. By contrast, the SEI formed under MPC current has low LiF content at its surface and high LiF content at its inner layer (Supplementary Fig. 22f), which is effective in blocking electron conduction without sacrificing Li ion transportation13,57. It is worth noting that the final MPC-SEI is rich in inorganic Li compounds (mainly Li2O, Supplementary Fig. 20f), which is different from the final CC-SEI with high organic C=O contents (Supplementary Fig. 19f). For the N 1s XPS depth profiles of CC-SEI and MPC-SEI, the MPC-SEI delivered a higher content (28.7%, Supplementary Fig. 23b) of highly conductive Li3N compounds than CC-SEI (26.9%, Supplementary Fig. 23a), which may also contribute to the better Li-ion transport through MPC-SEI than that of CC-SEI. The post-mortem XPS analysis also showed that the Li2O-rich SEI can be well retained at elevated temperature and after repeated cycling tests (Supplementary Figs. 24–27). The undesired Li stripping would produce dead Li, SEI crack, uneven interface, and so on. For the MPC plating protocol, the generated SEI has a high strength (modulus: 5.3 GPa) with an inorganic-rich structure dominated by Li2O (inner- and outer-layer) and low LiF (while mainly inner layer). Therefore, the discharging of the MPC protocol deposited Li metal has lower stripping overpotentials (5.9 mV, Fig. 3b) compared with those from the CC samples (7.8 mV) (Fig. 3a). This is expected from the lithiophilic Li|Li2O interface, which could attract the Li atoms quickly to fill the Li vacancies created by Li stripping near the Li|Li2O interface and maintain a smooth Li surface32,58.

The morphologies for the cycled Cu foils in Li||Cu half cells were also characterized by SEM and XPS. The cycled Cu foils in Li||Cu half cells through MPC protocol present more even surface morphologies and thinner by-product layers (2.2 μm after 50 cycles and 2.1 μm after ten cycles) than those under CC protocol (45.6 μm after 50 cycles and 19.1 μm after ten cycles), respectively (Fig. 3c-f and Supplementary Fig. 28). For the composition of reaction by-products layer, the one after MPC protocol has low content of LiCx, while the one using CC protocol is in clear contrast (Fig. 3g, h). The high contents of LiCx may perforate through the separator, causing battery inefficiency and safety concerns59. In addition, different from the CC charging protocol, the cycled Cu foil using the cell MPC protocol has higher surficial carbon content (mainly polymerized C-O and C=O groups, Fig. 3i, j), which is effective in protecting LMNE and re-activating the dead Li (see extended applications below).

COMSOL simulations for the maximum allowable current density
For practical usage, it is important to evaluate the largest plating current density that the as-formed SEI could sustain. To this end, COMSOL multiphysics simulation was carried out by combining the ternary current distribution, deformed geometry and solid mechanics modules (Fig. 4a–g, Supplementary Fig. 29 and Supplementary Table 3). It is worth noting that Fig. 4a–f are only part of the simulation cell (the observation window in Supplementary Fig. 29). Firstly, Li metal deposition process through CC and MPC protocols in Li||Cu half cells were simulated. Typically, the plating protocols of 1 mA cm-2 (0.75 mAh cm-2) in comparison with 0.5 mA cm-2 (0.25 mAh cm-2) - 1 mA cm-2 (0.5 mAh cm-2) were simulated with the SEI modulus being 1 and 2 GPa, respectively. The SEI yield strength is defined as 1% of the modulus60, and the Von Mises criterion was employed for the determination of SEI failure61. As shown in Fig. 4a–c, with 0.75 mAh cm-2 of Li metal deposited at 1 mA cm-2 continuously, the yield strength of SEI was reached, which mean that the SEI at this stage would be pierced and form the dendritic Li. By contrast, the accumulated stress of the 0.5 mA cm-2 (0.25 mAh cm-2) - 1 mA cm-2 (0.5 mAh cm-2) sample (Fig. 4d–f) is far below its yield strength, indicating that the higher modulus of SEI formed at lower current density could change the deposition electrochemical potential and boost Li metal uniformity. The simulation results show that the poor SEI strength formed by large current density (1 mA cm-2) cannot sustain the continuous current surge during the Li metal plating process, leading to the formation of porous Li metal deposition and a thick by-product layer on cycled LMNE. However, the strong SEI with high strength which was formed at a small current density (0.5 mA cm-2) can sustain the current surge during the continuous Li metal plating process, forming the densified Li metal deposition and thin by-product layer on cycled LMNE.

If we set the first 0.25 mAh cm-2 of Li deposited at 0.5 mA cm-2 with various SEI modulus and roughness, the maximum allowable current density (MACD) for the following Li deposition at 0.5 mAh cm-2 can be screened out (Fig. 4g, Supplementary Figs. 30–31). The results show that the high modulus and small roughness of SEI can increase the MACD. With the SEI modulus of 10 GPa and SEI amplitude (A) of 40 nm, the MACD could be as high as ~3.8 mA cm-2 (Supplementary Fig. 30). The simulated results are consistent with the Li metal morphologies shown in Fig. 4h, i and Supplementary Fig. 32, where the SEI formed at 0.5 mA cm-2 could sustain the current surge at 2 mA cm-2 and 3 mA cm-2, while the SEI formed at 1 mA cm-2 could not sustain the current surge even at 0.5 mA cm-2 and generate the porous Li metal.

Performance of IAF Li metal coin cells
The MPC charging protocol was further applied to cycle IAF Li metal coin cells coupled with two high mass loading layered oxide positive electrodes, such as polycrystalline LiNi0.6Mn0.2Co0.2O2 (NMC622, 28 mg cm-2) and single crystal LiNi0.8Mn0.1Co0.1O2 (SCNMC811, 26 mg cm-2). In addition to the constant charge mechanism at 1 mA cm-2 (CC, Fig. 5a), one MPC charge protocol was also proposed for IAF Li metal coin cells, as shown in Fig. 5b. The CC and MPC protocols demonstrate a similar tendency as that in the CC and MPC plating protocols for Li||Cu cells, respectively. As expected, the IAF Li metal coin cell charged through the MPC protocol showed a significantly better performance, delivering a longer cycle life and higher CEs (Fig. 5c, d). According to the potential-capacity profiles of the tested IAF Li metal coin cells, batteries charged through CC protocol demonstrate a faster capacity decay than those charged with MPC protocol (Fig. 5e–h). The morphologies of the 2nd plated LMNE in Cu||NMC622 full cell were also characterized by SEM. As shown in Supplementary Fig. 33a–d, the charged LMNE through CC protocol exhibits a porous surface, which is different from the flat surface of the MPC-charged one. After 20 cycles, the cycled negative electrode through CC protocol has more “dead Li” formation and thicker by-product layer than the MPC cycled negative electrode (Supplementary Fig. 33e–l), leading to the observed inferior cycling performance.

A constant capacity-constant potential charge for both the CC and MPC protocols was also designed to approximate the dynamic 100% SoC charge of Cu||NMC622 full cells, as shown in Supplementary Fig. 34. The cycling results clearly show that the MPC charged cell delivered better capacity retention than the CC charged cell, showing the merits of MPC protocol. The MPC protocol is also effective in decreasing the potential polarizations of LMBs with C@S positive electrode (Supplementary Fig. 35) and NMC622 positive electrode (Supplementary Fig. 36), and extending their cycle life. The cycling stability of graphite negative electrode under fast-charge conditions can also be increased via MPC charge protocol (Supplementary Fig. 37). The existence of lithium inventory at the lithiated and delithiated state of cycled graphite negative electrode was clearly reduced (Supplementary Fig. 38).

Extended applications
The MPC charging protocol is also applicable in the following categories: i) Prevent over-discharge; ii) IAF Li metal pouch cells. Upon calendar aging of 48 hours for the cycled IAF Li metal coin cells, severe over-discharge of the IAF Li metal coin cells charged through CC protocol was found (Fig. 5i, Supplementary Fig. 39c and Supplementary Fig. 40c, e), while such over-discharging is effectively suppressed through MPC charging (Fig. 5j, Supplementary Fig. 39d and Supplementary Fig. 40d, f). Moreover, as shown in Fig. 5k, l, the first cycle CEs of the IAF Li metal coin cells charged through MPC protocol after calendar aging is larger than the former ones (94.2% compared to 95.9% of CC protocol and 101.2% compared to 97.3% of MPC protocol in NMC622 IAF Li metal coin cells, and 94.3% compared to 96.1% of CC protocol and 99.8% compared to 98% of MPC protocol in SCNMC811 IAF Li metal coin cells), indicating that dead Li formed in the former cycles has been re-utilized by MPC protocol, while this is not the case for IAF Li metal coin cells charged through CC protocol. It is worth noting that for polycrystalline NMC622 (Supplementary Fig. 39a, b) or single-crystalline NMC811 positive electrode materials (Supplementary Fig. 40a, b), the above capacity-recovery performances of IAFLMBs can be achieved repeatedly. Since this reactivation process was carried out at the discharge state of LMBs, where the safety concerns of battery have been largely decreased compared to the battery with high SoC62. Therefore, it is easy to reactivate the dead Li across multiple modules in a large-scale battery without the need for other protection techniques.

A gradient MPC charging protocol (1.5 Ah-1.2 Ah-0.9 Ah) was further developed to charge-discharge 1.8 Ah (370 Wh kg-1) IAF Li metal pouch cells using a commercial-scale NMC622 positive electrodes (Supplementary Table 4). The cells were tested using conventional carbonate electrolyte (1 M LiPF6 in EC/DEC (v/v, 1/1) with 10 wt% FEC) and under a stack pressure of 800 kPa (Supplementary Fig. 41a, c). The results show that the MPC charge protocol could elongate its cycling life of 32 cycles for CC charge to 66 cycles and possess significantly higher CEs (98.5% compared to 97.5% of CC protocol, Fig. 6a-d). Although the state-of-charge (SoC) for the present CC or MPC charge protocol of IAF Li metal pouch cell is less than 100%, the IAF Li metal coin cell that was charged-discharged at 0.2 C (5 h charge) and 100% SoC (between 2.8 and 4.3 V) can only maintain 55.4% of its capacity after 30 cycles (Supplementary Fig. 42), which further shows the advantage of the MPC protocol in improving the cycling stability of IAFLMBs. In addition, the MPC charge protocol can improve the capacity retention of IAF Li metal pouch cell under ambient pressure conditions (Supplementary Fig. 41b, d), which could be cycled longer, especially at the high-capacity regime (Supplementary Fig. 43c–f). Replacing the conventional electrolyte with high concentration dual-salt electrolyte (2 M LiDFOB and 1.4 M LiBF4 in FEC/DEC (v/v, 1/2))23, the 1.5 Ah (400 Wh kg-1) IAF Li metal pouch cell with SoC of 80% could retain 80% of its capacity even after 298 cycles, which represents a significant advance over the reported IAF Li metal pouch cells10,23–26,63–69 (Fig. 6e, f and Supplementary Tables 4, 5).

Although the high current density at the middle step of charging process would produce more heat during the charge process, the temperature increase (~0.5 °C) is bearable for the charging station (Supplementary Fig. 44b). Whereas its smaller discharge temperature variation (~27.5 °C for MPC protocol versus ~29 °C for CC protocol) would benefit the service of battery during the discharge process. The pouch cell charged by MPC protocol delivered smaller potential polarizations when varying the pressure conditions (33 and 46.1 mV compared to 49 and 74.6 mV of CC protocol, respectively, Fig. 6a, b and Supplementary Fig. 43a, b). The smaller volume expansions for the cell charged through MPC protocol (Supplementary Fig. 45) is attributed to the thinner reaction by-product layer on the extracted separator for the terminated pouch cell (Supplementary Fig. 46), demonstrating the merit of the MPC protocol in suppressing the side-reactions during the cycling process. The failure mechanism of IAFLMBs and LMBs that were charged via CC current was different. As shown in Supplementary Fig. 47a, b, for both cycling protocols of CC and MPC, the IAFLMBs can still be operated continuously even though the terminated charge potential has reached 5 V vs. Li+/Li. This clearly shows that the IAFLMBs will fail gradually during the continuous cycling process. However, for the LMBs with N/P ratio of ~0.5 (Supplementary Fig. 47c, d), the cell with CC protocol displays an abrupt failure after its terminated charge potential reaching 5 V vs. Li+/Li, while the LMB cell with MPC protocol exhibits a gradual failure mechanism. The reason for the difference in failure modes between CC charged IAFLMBs and LMBs should originate from the difference in Li metal capacity. Due to the low capacity of active Li metal, the LMNE in IAFLMBs will corrode quickly, resulting in a shorter cycling life compared to LMBs. The short cycle life of IAFLMBs lies in its thinner by-product layer, which may be incapable of piercing through polymer separator and incur battery short-circuit. For LMBs, although its life will be longer, the accumulated by-product layer on the surface of LMNE will be more serious than that in IAFLMBs, which may incur the short-circuit of LMBs and result in the abrupt failure of LMBs eventually. The present MPC protocol exhibits high potential of practical applications in terms of the charge time, maximum charge power and cycling performance (Supplementary Figs. 3, 4 and Supplementary Tables 6, 7). The present research does provide extensive evidence to prove the effectiveness of MPC for enhancing the cycling stability of IAFLMBs, which could enlighten a bright future for its practical applications.

The formation of porous Li metal negative electrode (LMNE) was captured to happen upon continuous conventional CC charge of LMNE, leading to a porous Li metal structure with a large surface area. Upon further cycling, LMBs charged through CC protocol suffer from low CE, thick by-products and short life eventually. Whereas, for the MPC protocol of LMBs, the SEI formed at the initial stage possesses high strength and is capable of protecting it from current surging, directing the densified Li deposition with a small surface area and dense packing. When an IAF Li metal coin cell is charged via the MPC protocol, it delivers high CEs, thin by-products and long cycle life. In addition, this protocol is applicable for preventing over-discharge and gradient charging of a large Li metal pouch cell with initially anode-free configuration (1.5 Ah (400 Wh kg-1)). This strategy provides both methodological and conceptual advancements for the development of high-performance LMBs, example of which could have a broad impact on not only liquid batteries, but also facilities such as safe high-energy solid-state batteries, portable devices and chemical or electrochemical reactions with limiting factors such as time, space and materials transfer.

Methods
Materials
Dehydrated alcohol solvent, N-methylpyrrolidone (NMP) solvent, fluoroethylene carbonate (FEC) and LiNO3 particles with analytical grade were purchased from Aladdin (Shanghai, China). The copper foil (thickness: ~10 μm), aluminum foil (thickness: ~20 μm), carbon black (Super P), carbon nanotubes (CNTs), polypropylene (PP, Celgard 2400) separator (thickness: ~20 μm), double ceramic (Al2O3)-coated PP membrane (with film thickness of 14 μm and coating thickness of 3 μm), polycrystalline LiNi0.6Mn0.2Co0.2O2 powder, single-crystalline LiNi0.8Mn0.1Co0.1O2 powder, 2032-type coin-cell cases, springs, and spacers and metallic foil (with diameter of 16 mm and thickness of 100 μm, Li content ≥99.9%) were purchased from Canrd Technology Co. Ltd. The electrolyte of 1 M lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in DOL/DME = 1/1 vol, 1 M lithium hexafluorophosphate (LiPF6) in EC/DEC (v/v, 1/1), and polyvinylidene difluoride (PVDF 5130, MW=1,300,000) were purchased from Dodo Chem. All solvents were stored over 4 Å molecular sieves for 48 h before use. All the electrolytes were prepared in a glove box filled with argon gas (H2O <0.1 ppm, O2 <0.1 ppm).

Preparation of negative electrodes, positive electrodes, and separators
To prepare Cu current collectors, commercial Cu foil was punched into slices 12 mm and 16 mm in diameter, respectively. Then the obtained Cu slices were immersed in anhydrous alcohol. After 30 min of ultrasonic washing, they were dried in a vacuum oven at 60 °C for 12 h. Afterwards, the Cu slices were transferred to a glovebox (H2O <0.1 ppm, O2 <0.1 ppm) for future usage.

The high loading LiNi0.6Mn0.2Co0.2O2 (NMC622, 28 mg cm-2) and single crystal LiNi0.8Mn0.1Co0.1O2 (SCNMC811, 26 mg cm-2) positive electrodes were prepared via the slurry-coating method. Typically, the pre-dried active material (NMC622 and SCNMC811), Super P and PVDF were mixed in a mass ratio of 8:1:1. After grinding in a mortar, stir mixing with NMP in a beaker for 6 h, the as-formed slurries were blade-coated on the Al foil. Upon evaporation of NMP in an oven at 80 °C, the Al supported positive electrodes were punched into slices 12 mm in diameter. Upon weighing and further drying in vacuum oven at 60 °C for 12 h, these slices were transferred to the glovebox. Before usage, the PP was punched into slices with diameter of 19 mm. After being washed with anhydrous alcohol and further dried in the vacuum oven at 60 °C for 12 h, it was transferred to the glovebox for future usage.

Assembly of coin cells
To evaluate the CEs, Cu foil (12 mm) was matched with Li foil to assemble CR2032 coin cells. The separator used here is PP, and the electrolyte for Li||Cu cells is 1 M LiTFSI in DOL/DME (v/v, 1/1) with 1 wt% LiNO3, if not stated otherwise. Initially anode-free (IAF) Li metal coin cells were fabricated by matching high loading positive electrodes (NMC622 or SCNMC811) with Cu foil (16 mm) directly. The electrolyte employed here is 1 M LiPF6 in EC/DEC (v/v, 1/1) with 10 wt% FEC. In this research, 60 μL of electrolyte were used for coin cell tests. To evaluate the cycling performances of Li metal cells (with N/P ratio of 0.6), the Cu@Li anodes were prepared first. Typically, two Li||Cu half cells with the electrolyte of 1 M LiPF6 in EC/DEC (v/v, 1/1) with 10 wt% FEC were assembled. After five cycles of activation at 0.05 mA cm-2 within the potential range of 0.01~1 V vs. Li+/Li, Li metal was plated on the Cu foil at 3 mAh cm-2 via CC current in both Li||Cu half cells. Then, the as-formed Cu@Li negative electrodes can be obtained by disassembling these two half cells.

Assembly of IAF Li metal pouch cells
The preparation of 1.8 Ah (370 Wh kg-1, ~18 g in total mass) IAF Li metal pouch cells was carried out in Guangdong Graphene Innovation Center. Typically, the dried NMC622 particles were mixed with PVDF, Super P and carbon nanotubes (CNTs) at a mass ratio of 95:3:1.8:0.2, respectively. After mixing with NMP to form a homogenous slurry, it was coated on the Al foil (16 μm) double-sided with an areal-loading of 30 mg cm-2. After drying, the coatings were sliced into NMC622 positive electrode (56 mm × 657 mm). The thickness of the Cu foil used in the present IAF Li metal pouch cell is 9 μm, with dimensions of 58 mm × 570 mm. Then the above electrodes were wound with a ceramic-coated PP membrane. The width of the rolling needle is 34 mm and the amount of rolling layer is 14. Upon assembled with Al-plastic film and injected with electrolyte (1 M LiPF6 in EC/DEC (1/1, v/v) with 10 wt% FEC, 3 g Ah-1), the un-activated IAF Li metal pouch cells were obtained. Before ex-factory test, these cells were first charged to 4.3 V at a current of 225 mA and then discharged to 3.0 V at the same current, as shown in Supplementary Fig. 43a.

For the preparation of 1.5 Ah (400 Wh kg-1, ~12 g in total mass) IAF Li metal pouch cells, the dried LiNi0.9Mn0.05Co0.05O2 (NMC90) particles (provided by Guangdong Graphene Innovation Center) were mixed with PVDF, Super P and carbon nanotubes (CNTs) at mass ratio of 95:3:1.8:0.2, respectively. After mixing with NMP to form a homogenous slurry, it was coated on the Al foil (10 μm) double-sided with areal loading of 22 mg cm-2. After drying, the coatings were sliced into NMC90 positive electrode (56 × 567 mm). The bare Cu foil (9 μm) was sliced into a negative electrode with dimensions of 59 × 475 mm. Then the above electrodes were wound with PP membrane. The number of rolling layers is 12. Upon assembled with Al-plastic film and injection with electrolyte (2 M LiDFOB and 1.4 M LiBF4 in FEC/DEC (v/v, 1/2)23, 2 g Ah-1), the un-activated IAF Li metal pouch cells were obtained. Before the ex-factory test, these cells were first charged to 4.5 V at a current of 225 mA and then discharged to 3.0 V at the same current, as shown in Supplementary Fig. 43b.

Characterization
X-ray photoelectron spectroscopy (XPS) was adopted to explore the chemical information of SEI and cycled electrodes. A PHI 5000 VersaProbe II XPS with Al Kα irradiation (1486.6 eV) was employed. SEM was utilized to characterize the morphologies of Li metal and the cycled electrode morphologies by using a cold field scanning electron microscope (SU8010, HITACHI) at 5 kV. AFM characterization was carried out to determine the surface fluctuation and Young’s modulus of SEI. Typically, the facility (Bruker, DIMENSION ICON) was placed in an Ar-filled glovebox (MBRAUN, H2O <0.1 ppm, O2 <0.1 ppm), and the AFM images were collected based on the PeakForce tapping mode. The modulus was obtained through the quantitative nanomechanics mode (QNM) and further fitting the curve using Derjaguin-Muller-Toropov (DMT) model. As an extension of the PeakForce tapping mode, the QNM can provide the modulus maps by analyzing the force at each scan point. It is worth noting that the preparation and ex-situ measurements of the electrode samples were carried out at a temperature range of 25 ± 1 °C. As to the electrochemical impedance spectrum (EIS) test, the Li||Cu cells were fabricated and cycled 5 times at 0.05 mA cm-2 within the potential of 0.01 V and 1 V firstly. Then, a fixed capacity of Li metal (0.25 mAh cm-2 or 3 mAh cm-2) was deposited on Cu foil through CC or MPC protocol, respectively. The Li||Cu@Li cells were kept under -20 °C, -10 °C, 0 °C, 10 °C, 20 °C, 30 °C to record the temperature-dependent EISs (with a frequency range from 100,000 Hz to 0.1 Hz and an amplitude of 5 mV (potentiostatic, Steps/Decade = 10, quasi-stationary potential)).

Electrochemical tests
All the Li||Cu half cells were cycled five times at 0.05 mA cm-2 within the potential between 0.01 V and 1 V before further test. For the Coulombic efficiency (CE) test, Li metal was deposited on Cu foil at 3 mAh cm-2 through each protocol and followed with stripping to 1 V at 1 mA cm-2. The plating current densities are listed in Supplementary Table 1. To test the average CEs, the Li||Cu cells were pre-cycled one time through CC-1 mA (6 h) and MPC-2 mA-3rd (6 h): 0.5 mA cm-2 (1 h)-1 mA cm-2 (1 h)-2 mA cm-2 (1 h)-1.5 mA cm-2 (1 h)-0.5 mA cm-2 (1 h)-0.5 mA cm-2 (1 h) protocols (both charged to 1 V at 1 mA cm-2), respectively. Then Li (QT) was deposited on Cu foil at 6 mAh cm-2 through CC-1 mA (6 h) and MPC-2 mA-3rd (6 h), followed by charge-discharge with a capacity of 3 mAh cm-2 (QC) for 11 cycles through CC (3 h) or MPC (3 h) protocols. Finally, the capacity when stripping to 1 V was measured (capacity: QS), and the average CEs can be calculated as: (11QC + QS)/(11QC + QT).

To compare the electrochemical performance of different charge protocols such as the pulsed current36,70, the asymmetrical bidirectional current38, the self-heat current40-9 mA cm-2, the seed current41-20 mA cm-2, the seed current42-50 mA cm-2 and the middle peak current in present research, Cu foil (12 mm) was matched with Li foil to assemble Li||Cu coin cells. Typically, the electrolyte here is 1 M LiPF6 in EC/DEC (1/1, v/v) with 10 wt% FEC, which is the same as the electrolyte for IAF Li metal coin cells. The test methods for these protocols are listed as follows: CC current, with continuous constant plating current of 1 mA cm-2; Asymmetric bidirectional charge protocol, with Li metal deposited at 1 mA cm-2 for 0.5 h and then it was followed by stripping Li metal at 1 mA cm-2 for 2 min (120 s), which was repeated 6 times and then followed by plating Li metal at 1 mA cm-2 for 12 min (720 s); Pulsed charge protocol, with Li metal deposited at 1 mA cm-2 for 0.5 h and then it was followed by remaining open circuit potential (OCP) for 2 min, which was repeated 6 times; Self heat-9 mA cm-2 charge protocol, with Li metal deposited at 9 mA cm-2; Seed current-20 mA cm-2 charge protocol (20 mA-1 mA), with Li metal deposited at 20 mA cm-2 for 3 min (180 s) firstly and then it was followed by plating Li metal at 1 mA cm-2; Seed current-50 mA cm-2 charge protocol (50 mA-1 mA), with Li metal deposited at 50 mA cm-2 for 4 s firstly and then it was followed by plating Li metal at 1 mA cm-2; MPC charge protocol, with Li metal deposited at 0.5 mA cm-2 for 0.5 h, 1 mA cm-2 for 0.5 h, 2 mA cm-2 for 0.5 h, 1.5 mA cm-2 for 0.5 h and 0.5 mA cm-2 for 1 h continuously. It is worth noting that for all these plating protocols, the total amount of Li metal deposited is 3 mAh cm-2 and the deposited Li metal was stripped at 1 mA cm-2 until the potential of Li||Cu half cells reach 1 V.

For the charge-discharge of IAF Li metal coin cells and Li metal coin cells, all the cells were charged for 3 hours with specified charge protocol and then discharged to 2.8 V (NMC622, SCNMC811) at 1 mA cm-2. For the 0.2 C charge-discharge of IAF Li metal coin cells (with NMC622 positive electrode) between 2.8 and 4.3 V (100 SoC) and under CC, the charge-discharge current was based on the theoretical capacity of 180 mAh g-1 for NMC622. For the 1.8 Ah IAF Li metal pouch cells, 5 hours gradient charge with Li capacity of 1.5 Ah, 1.2 Ah and 0.9 Ah were carried out sequentially. In addition, for the 1.5 Ah IAF Li metal pouch cells, 3 hours gradient charge with Li capacity of 1.2 Ah and 0.9 Ah were carried out sequentially. Details for pouch cell test are available in Supplementary Table 4. All the coin and pouch cells were cycled at the temperature range of 25 ± 1 oC.

Simulation
The simulation domain of electrolyte/separator is shown in Supplementary Fig. 14. The non-uniform SEI surface is mimicked by a cosine function with amplitude A (y=200+Acosωπx, where ω=1:3 and A=40 or 50 nm). The current density boundary condition and symmetric boundary are applied to the top boundary and the two side-boundaries, respectively.

The ternary current distribution, deformed geometry and solid mechanics modules of COMSOL multiphysics were used in simulation of the plating/stripping of Li and the mechanical response of SEI. Charge and species conservation laws govern the evolution of concentration and electrical potential with ion flux given by Nernst-Planck equation71:

Ji = -Di ∇ci - zi ui Fci ∇ϕ

where subscript i denotes ionic species i, Ji, Di, ci, zi, ui are the ion flux, diffusion coefficient, concentration, charge carried, and mobility of species ionic species i, respectively. F is the Faraday’s constant and ϕ is the electrical potential of electrolyte.

Bulter-Volmer equation was utilized to describe the electrochemical kinetics at interface:

iloc = i0 [exp(αa Fη/RT) - exp(-αc Fη/RT)]

where iloc is the local current density; i0 is the exchange current density; η is the reaction overpotential; αa and αc are the transfer coefficients for anodic and cathodic reactions, respectively; CR and C0 are the dimensionless concentration, respectively; R is the idea gas constant; and T is the absolute temperature.

The SEI was considered as an elastic material60. The thickness of Li deposition is calculated by the ternary current distribution and deformed geometry modules of COMSOL and is imposed as the prescribed normal displacement at the SEI-Li interface. No initial residual stress is considered in SEI. Stress distribution in the domain was solved by quasi-static assumption:

∇·σ=0

where σ is the Cauchy stress tensor.

The influence of deformed SEI on electrochemical kinetics is taken into account by introducing a factor term in the Butler-Volmer equation72,73:

B = exp(γΔμe/RT)

where the electrochemical potential change Δμe resulting from local strain is assumed to be proportional to the Young’s modulus of SEI. A form of B = exp(κ(ESEI - E0)) is adopted for illustrative purpose. If modulus of SEI is higher than the modulus E0, its effect on electrochemical potential change is included. Value of E0 is taken as 1 GPa and scaling parameter κ takes the value of -0.3. Other parameters used in the simulation are listed in Supplementary Table 3.

To obtain the maximum allowable current density (MACD) for the SEI with various modulus and SEI roughness, the first 0.25 mAh cm-2 of Li was deposited at 0.5 mA cm-2, then the following 0.5 mAh cm-2 of Li was further deposited at various current densities. The Von Mises criterion was employed for the determination of SEI failure61. Through continuous simulations at specific SEI modulus and amplitude, one could get the MACD for the following 0.5 mAh cm-2 of Li metal plating.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this work, the authors propose a “volcano-curved stepwise” (V) current protocol, wherein the Li plating current is small at the beginning, ramps up to a peak in the middle of the charge, and then ramps back down at the end of the charge. Their findings indicate that this novel charging regimen generates a dense and robust lithium deposit with a favorable solid-electrolyte interphase (SEI). They demonstrate stable anode-free coin cells (with high-loading cathodes up to ~28 mg cm^-2) and pouch cells (1.5–1.8 Ah) that run for extended cycles with high capacity retention.\nAs a reviewer, I feel that substantial work needs to be done to provide in-depth new knowledge and a comprehensive understanding of the problem to consolidate this work. I’d like to raise the following questions:\n1. The authors observe a Li₂O-dominant SEI with inward LiF distribution under volcano plating.\n– How does the presence of Li₂O (vs. LiF) at the outermost surface favor Li-ion transport and mechanical strength?\n– Could other inorganics (e.g., Li₃N in specialized electrolytes) further improve these mechanical/transport properties?\n2. The XPS depth profiles indicate a gradient of organic and inorganic species from surface to bulk.\n– How stable is this gradient under high-temperature cycling or repeated current surges?\n– Does the authors’ methodology address how the SEI might evolve past tens of cycles?\n3. AFM results show initial SEI moduli can range from 1–2 GPa at low current densities, and up to ~5 GPa after multi-step plating.\n– How were these AFM measurements controlled to ensure minimal damage to a soft Li substrate to get an accurate measurement?\n- Why the Young’s modulus will change? This is probably one of the most important questions that need to be answered in this research work such that we can understand the entire mechanism. Without the explanation, I am not convinced by all the optimized lithiation protocols.\n- The follow-up numerical simulation also uses the failure strain which actually is more important than Young’s modulus in mechanical failure. However, the tests cannot show the failure strain.\n4. Regarding COMSOL setups:\n– How sensitive are the results to assumptions about yield strength (taken as ~1% of Young’s modulus)?\n– Does localized variation in SEI thickness or roughness at the microscale alter these macroscale conclusions?\n5. The authors present significantly improved Coulombic efficiencies in Li‒Cu half-cells under V vs. constant current.\n– How might similar “V” profiles be adapted for faster charge/discharge rates (beyond 2–3 mA cm^-2)?\n– Could dynamic adjustments (e.g., real-time feedback from the voltage slope) further optimize the wave shape?\n6. Anode-free pouch cells were tested with partial states-of-charge (SoC).\n– In a fully charged scenario (100% SoC between 2.8 and 4.3 V for NMC), how do cycle lifetimes compare?\n– What is the trade-off between partial SoC operation and the practical demands for maximum energy?\n7. Over-Discharge Prevention: The study shows that, after rest or calendar aging, the “V” protocol can re-activate dead Li to some extent.\n– Are there additional protective measures to ensure this reactivation step is consistent across multiple modules in a large-scale battery?\n– Could similar approaches mitigate lithium plating issues in conventional graphite-anode cells at high rates?\n8. High Loading Cathodes: With ~28 mg cm^-2 cathodes, the volumes of plated Li can be large.\n– How do you track potential “hot spots” and localized Li depletion across the Cu surface over 100+ cycles?\n– What failure mechanisms appear first at the large format level: excessive SEI consumption, partial cell shorting, or cathode fatigue?\n9. The authors present cross-sectional SEM images of used electrodes and separators.\n– In the event of micro-cracks or short-circuits, does the volcano protocol fail abruptly or gradually?\n– Would in situ tomography (e.g., synchrotron X-ray or neutron imaging) capture these morphological changes more completely?", "reviewer_2": "The authors propose a potential-varying charge profile to alter and improve lithium metal deposition for anode-free lithium metal batteries. Specifically, their proposed current rates start small, peak in the middle of the charge step, and end small. They propose that the voltage-varying protocol leads to a higher strength SEI that is more rate capable. The results are interesting, but I have some critiques on the proposed mechanism and presented data.\nOverall, the manuscript was a bit difficult to parse because there are too many referenced supplementary figures, and I would recommend somehow highlighting or consolidating the most important figures that make the authors’ point. Even though I have both the SI and the main opened up at the same time, it takes awhile to go back and forth and view every single SI figure. There are many parameters explored, and some I am not sure have a big impact. For example, does a temperature difference of 1.5degC briefly at the beginning of the discharge step really have that big of an impact (SI Figure 37)?\nThe difference in measured modulus from AFM is one of the author’s main arguments for why they see performance improvements. However, the AFM only captures a very small section of the leectrode, and we have to assume that it is representative of the entire electrode. What is the variation in modulus across different parts of the electrode?\nWhile the authors show some reproducibility in Figure 1, it would be more compelling if the authors can show the spread of their results in Figure 5 and 6. It appears that in many of the cases in Figures 5-6, cell failure occurs rapidly and within just 1 or 2 cycles. This is often indicative of electrolyte dry out. On the other hand, the cells in Figure 1 show more gradual capacity fade, indicating gradual passivation and SEI growth.\nI was confused why the pouch cells in Fig 6 were cycled in a different protocol than the other cells. Why do subsequent cycles undergo less charge capacity (why is the discharge capacity decreased from 1.5 to 1.2 Ah and then to 0.9 Ah?)\nThe authors conclude that the “SEI rupture is captured to happen..” (line 339) but rupturing is not presented anywhere in the manuscript and there is no physical evidence of SEI rupturing.", "reviewer_3": "The authors discuss alternate Li plating protocols to achieve more dense and more uniform metallic Li-films.\nPlease consider to not call this a volcano like shape but rather V shaped protocol because a) it will be confusing for people from the field of catalysis and b) this is an inverted volcano ... a crater? => better call it V-shaped or crater shaped if you like. Actually looks like a excavator made crater.\nThere has been a lot of work on metallic anodes in liquid and solid state electrolytes and most of that work is not properly discussed and as such the manuscript lacks behind what it could offer as insight for the community.\nThere is great work from Axel Groß that discusses barrier height as a reason for dendrite growth in Li and Na but the absence in Mg and Ca. There is also work by the entire community of electroplaters that lead to the design of a pulsed protocol by Wolfgang Schuhmanns group that showed that it is possibile to exceed 6000 cycles for a metallic anode. There is also work on non-linear charging protocols by soem authors that show differences. As I understand growth of thin films we have an incoming ion energy (usually low here), surface diffusion and bulk diffusion. Initially the authors observe a very low potential vs. Li/Li+ and then a levelling off at lower potentials for the constant case. This looks to me that as long as there is no improper seed or if the seeds were destroyed the effect would be the same. Can the authors maybe perform an experiment of a constant current charging for like 0.3 mAh/cm2 then make a short same current reverse pulse of the same current density of 0.05 mA/cm2 and then continue charging normally? This would then allow a better discussion.\nThe morphology in some figures look a lot like for a thompson structure zone diagram. consider discussing it in this context.\nDendrite and island growth and so on depend on curvature which is not discussed.\nYoungs modulus will depend on defect density. This is not discussed.\nLithium is extremely soft and the stresses discussed would be enough for plastic deformation. Please add a discussion of curvature, surface diffusion in context to deposition rate.\nIn the introduction authors state that \"battery performance significantly varies with charging and discharging protocols\" I believe this warrants a bit of discussion. Some testing protocols are designed to measure performance but I think few tests are designed with degrading performance (except abusive tests) such that I think some additional discussion should be done here.\n\"generally in a 62 “stressed” state,\" I understand that this is referring to thin film stress but maybe explain a bit what this means to the not knowing audience. cosider adding the citations at the endo f the sentence as it loks like strange Sn and Cu isotopes.\nmonor rephrasing remarks:\nIn figure 1 and throughout the manuscript please consider rephrasing \"V current\" and \"C current\".\nthe previous abandoned choice -> should be rephrased"}, "author_response": "A point-by-point response to reviewer’s comments\nCOMMENTS TO THE AUTHOR:\nReviewer #1 (Remarks to the Author):\nIn this work, the authors propose a “volcano-curved stepwise” (V) current protocol,\nwherein the Li plating current is small at the beginning, ramps up to a peak in the\nmiddle of the charge, and then ramps back down at the end of the charge. Their findings\nindicate that this novel charging regimen generates a dense and robust lithium deposit\nwith a favorable solid-electrolyte interphase (SEI). They demonstrate stable anode-free\ncoin cells (with high-loading cathodes up to ~28 mg cm^-2) and pouch cells (1.5–1.8\nAh) that run for extended cycles with high capacity retention.\nAs a reviewer, I feel that substantial work needs to be done to provide in-depth new\nknowledge and a comprehensive understanding of the problem to consolidate this work.\nI’d like to raise the following questions:\nAuthor reply: We thank the reviewer for your effort in reviewing our manuscript.\nFollowing your constructive comments, we have carried out extensive new experiments\nto address your concerns and improve the quality of the revised manuscript. A point-\nby-point response is listed as follows:\n1. The authors observe a Li₂O-dominant SEI with inward LiF distribution under\nvolcano plating.\n– How does the presence of Li₂O (vs. LiF) at the outermost surface favor Li-ion\ntransport and mechanical strength?\n– Could other inorganics (e.g., Li₃N in specialized electrolytes) further improve these\nmechanical/transport properties?\nAuthor reply: Thank you for the insightful comments!\n1) Li O (vs. LiF) favored Li-ion transport.\ncompounds (mainly Li O), which is different from the constant current (CC) produced\n2\nion transport of MPC-SEI should result from its higher content of Li O, because the Li+\n2\nion conductivity of Li O is 10-9-10-6 S cm-1, which is significantly higher than that of\ninterface between Li metal and inorganic compounds such as Li O, LiPON, Li CO and\n2 2 3\nLiF is: Li/Li O > Li/LiPON > Li/Li CO > Li/LiF2. The more lithiophilic the interface\n2 2 3\n1\nis, the smoother the Li surface can be maintained during the stripping process of Li. In\naddition, the wetting behavior for Li/Li O can be termed as “lithiophilic”, while it is\n2\n“lithiophobic” for Li/LiF. And therefore, the Li O dominated MPC-SEI is more\n2\nfavorable for Li-ion transport than the CC-SEI.\n2) The improved mechanical strength of MPC-SEI compared with CC-SEI.\nFor the SEI on Li metal anode, the high modulus of SEI which formed at small current\ndensity should result from its high content of inorganic compounds3. In our middle peak\n(MPC) current, the initial and last current was much smaller than the peak current at\nthe middle step. Since the SEI formed at large current density is less stable than that\nformed at small current density, the final small current density is helpful in increasing\nthe mechanical strength of MPC-SEI. From the viewpoint of SEI composition, we think\nthat the surface Li O-rich structure is important for the high modulus of MPC-SEI,\n2\nwhile this may not be the only reason. Because the carbon content of the CC-SEI is also\nhigher than that of MPC-SEI, and the low content of organic species of MPC-SEI may\nalso contribute to its high mechanical strength.\n3) Influences of other inorganics (for example, Li N) on mechanical/transport\n3\nproperties.\nFollowing the reviewer’s comments, we have re-analyzed the N1s XPS depth profiles\nof CC-SEI and MPC-SEI, as shown in Figure R1. It can be clearly seen that the MPC-\nSEI delivered higher content (28.7%) of highly conductive Li N compounds than\ncompared to CC-SEI.\nAccording to the variation of atomic concentrations during the continuous CC (Figure\nR2) or MPC (Figure R3) plating process, the variation of element nitrogen is less\nsignificant than the variations of element carbon and oxygen. As shown in Figure R2,\nthere is a significant increase of carbon content whereas decrease of lithium content\nwhen the Li capacity increased from 0.75 mAh cm-2 (CC2) to 1.75 mAh cm-2 (CC3).\nThis is highly correlated with the formation of porous lithium metal anode, which\nresults in the increased solvent degradation and forming the organic-rich SEI. Such kind\nof organic-rich SEI will remain on the surface of lithium metal anode even after 3 mAh\ncm-2 of Li metal was deposited via constant current.\nBy contrast, there is no significant increase of the carbon or oxygen element for the SEI\nduring the stepwise deposition of MPC current (Figure R3). It is worth noting that there\nis also concentration increase of carbon element when the Li capacity increased from\n0.75 mAh cm-2 (MPC2) to 1.75 mAh cm-2 (MPC3). This may result from the peak\n2\ncurrent (here is 2 mA cm-2) of MPC protocol, which will induce the formation of\norganic-rich SEI. Nevertheless, since the time of peak current is short and the initially\nformed SEI at 0.5 mA cm-2 is strong enough, the as-deposited Li metal will always\nremain its densely packed structure. As a result, after the plating of final 0.5 mAh cm-2\nof Li metal at 0.5 mA cm-2, the MPC-SEI delivers an ultrahigh mechanical strength of\n5.3 GPa.\nUpon revision, Figure R1 has been added as Supplementary Fig. 23. The following\ncontents have also been added into our revised manuscript.\nFor the N1s XPS depth profiles of CC-SEI and MPC-SEI, the MPC-SEI delivered higher\ncontent (28.7%, Supplementary Fig. 23b) of highly conductive Li N compounds than\nion transport of MPC-SEI compared to CC-SEI.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nAgain, thank you for the insightful comments.\nFigure R1. N1s XPS depth profiles of a, CC6 sample; b, MPC6 sample, respectively.\nsample, respectively.\nFigure R3. Atomic concentrations for the XPS depth profiles on a-f, MPC1 to MPC6\nsample, respectively.\n4\n2. The XPS depth profiles indicate a gradient of organic and inorganic species from\nsurface to bulk.\n– How stable is this gradient under high-temperature cycling or repeated current surges?\n– Does the authors’ methodology address how the SEI might evolve past tens of cycles?\nAuthor reply: Thank you for the constructive comments!\nFollowing the reviewer’s suggestions, we have carried out the high temperature (60 oC)\ntests of Li | Cu cells with ether electrolyte (1M LiTFSI in DOL/DME (v/v, 1/1) with\n1wt% LiNO ), as shown in Figure R4. In addition, we have also conducted the XPS\n3\ncharacterizations on LMA after 20 cycles (i.e., the 21st plated LMA), as shown in Figure\nR5-R8.\nAs shown in Figure R4, the LMAs which were plated through MPC current showed\nhigher average CEs (ACE, 98.4% for cell 1 and 98.3% for cell 2) than that of LMAs\nwith CC current (96.9% for cell 1 and 96.7% for cell 2). The above results clearly\nshowed that our MPC current is also effective in stabilizing LMA under high\ntemperature cycling conditions.\nFor the SEI on the 21st plated LMA and at 25 oC, the CC-SEI is rich in organic -CF\nx\nspecies (Figure R5, R6) and LiN O species (Figure R7), while the MPC-SEI is\nx y\ndeficient of these two species. In addition, the CC-SEI is deficient in surface Li O\n2\ncompounds (Figure R8), while the MPC-SEI can retain its surface Li O-rich structure\n2\neven after 20 cycles. The organic rich (-CF species) and surface Li O deficient\nx 2\nstructure of CC-SEI will impede its Li-ion transport significantly, while this is not the\ncase of MPC-SEI which can still retain the surface Li O-rich structure even after 20\n2\ncycles.\nFor the SEI on the 21st plated LMA and at 60 oC, the formation of organic species has\nbeen largely suppressed, which agrees well with the reported research where increasing\nthe cycling temperature of LMA will effectively lower the content of organic species in\nSEI4. However, the content of organic species in CC-SEI is still larger than that of MPC-\nSEI (Figure R5, R6), which agrees well with the cycling results in Figure R4 where the\nexistence of relatively higher content of organic species may reduce the cycling stability\nof LMA which was plated via CC current. In addition, although the content of Li O at\n2\nthe inner layer of CC-SEI has been increased when the temperature was increased from\n25 oC to 60 oC, its surface is still lacking enough Li O content to achieve fast Li-ion\n2\ntransport, which is in contrast to the conditions of MPC-SEI where its surface Li O\n2\ncontent increased when the temperature increased from 25 oC to 60 oC.\n2\nwell retained even at high temperature and continuous cycling conditions, showing the\nadvantage of our MPC current in improving the cycling efficiency of LMA.\nUpon revision, Figure R4, R5, R6, R7 and R8 has been added as Supplementary Fig.\n2a, Supplementary Fig. 24, Supplementary Fig. 25, Supplementary Fig. 26 and\nSupplementary Fig. 27, respectively. The following contents have also been added to\nour revised manuscript.\nIn addition, the MPC protocol also demonstrates higher average CEs (Supplementary\nFig. 1) and better cycling stability at 60 oC (Supplementary Fig. 2a), and higher CEs\nunder an areal capacity of LMA of 0.3 mAh cm-2 (Supplementary Fig. 2b-d) or 6 mAh\ncm-2 (Supplementary Fig. 2e-g).\nPost-mortem analysis showed that the Li O-rich SEI can be well retained at elevated\n2\ntemperature and after repeated cycling (Supplementary Figs. 24-27)\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nAgain, thank you for the constructive comments.\nFigure R4. Coulombic efficiencies (CEs) of Li | Cu cells where the Li metal was\ndeposited at 60 oC and through CC and MPC protocols. Two duplicates for each\nprotocol were tested to minimize operational error.\nCC current at 25 oC; b, MPC current at 25 oC; c, CC current at 60 oC and d, MPC\ncurrent at 60 oC, respectively.\nFigure R6. F1s XPS depth profiles on the surface of 21st deposited Li metal through a,\nCC current at 25 oC; b, MPC current at 25 oC; c, CC current at 60 oC and d, MPC\ncurrent at 60 oC, respectively.\nFigure R7. N1s XPS depth profiles on the surface of 21st deposited Li metal through a,\nCC current at 25 oC; b, MPC current at 25 oC; c, CC current at 60 oC and d, MPC\ncurrent at 60 oC, respectively.\nCC current at 25 oC; b, MPC current at 25 oC; c, CC current at 60 oC and d, MPC\ncurrent at 60 oC, respectively.\n3. AFM results show initial SEI moduli can range from 1–2 GPa at low current densities,\nand up to ~5 GPa after multi-step plating.\n– How were these AFM measurements controlled to ensure minimal damage to a soft\nLi substrate to get an accurate measurement?\nAuthor reply: Thank you for the insightful comments! Your comments are important to\nsubstantiate our research.\nTo answer the reviewer’s questions, we have further characterized the modulus of SEI\nafter stripping all the deposited Li metal of CC1 and MPC1 samples. And therefore, the\ninfluence of soft Li metal substrate can be largely reduced. The modulus of SEI was\ntested at three positions to reduce the errors. As shown in Figure R9a, the modulus of\nSEI formed on MPC1 sample is also higher than that of CC1 sample, aligning well with\nthe tested modulus at the existence of soft Li metal substrate (Figure R21).\nUpon revision, Figure R9a and Figure R9b-g has been added as Supplementary Fig.\n11a and Supplementary Fig. 13a-f, respectively. The following contents have also been\nadded into our revised manuscript.\nTo reduce the accidental errors of modulus test which may be caused by the position\nvariations of electrodes, we have conducted the modulus tests at three positions of LMA\ntotally, as shown in Supplementary Fig. 11a.\nAlthough the modulus of SEI will change when the positions are varied, the averaged\nvalues of MPC1 sample (2.3 GPa) and MPC6 sample (4.9 GPa) are still significantly\nhigher than that of CC1 sample (1 GPa) and CC6 sample (2.5 GPa), respectively,\ndemonstrating the advantage of our MPC protocol in forming SEI with high mechanical\nstrength (Supplementary Fig. 11b and Supplementary Fig. 12). When the plated Li\n8\nmetal was fully stripped, the tested modulus of MPC1 sample is also higher than that\nof CC1 sample (Supplementary Fig. 13), aligning well with the above modulus analysis.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nAgain, thank you for the insightful comments.\nFigure R9. a, Schematic showing the positions of samples which were used to conduct\nAFM characterizations. b, c, d, Young’s modulus distribution maps (the inset number\nis the mean value of each sample) on the surface of Cu in Li | Cu cell, where lithium\nmetal was plated on Cu via CC current and then stripped to 1V vs. Li+/Li. e, f, g,\nYoung’s modulus distribution maps (the inset number is the mean value of each sample)\non the surface of Cu in Li | Cu cell, where lithium metal was plated on Cu via MPC\ncurrent and then stripped to 1V vs. Li+/Li.\n- Why the Young’s modulus will change? This is probably one of the most important\nquestions that need to be answered in this research work such that we can understand\nthe entire mechanism. Without the explanation, I am not convinced by all the\noptimized lithiation protocols.\nAuthor reply: Thank you for these insightful and important questions!\nGenerally, the SEI on LMA is a solid film, and it requires high mechanical strength,\nlow reactivity and low solubility simultaneously. However, the initially formed SEI is\nthin (<10 Å) and is incapable of suppressing electron tunneling, which will result in\nfurther electrochemical decomposition of electrolyte and thickening of SEI. Therefore,\nduring the long-term plating process of LMA, the as-deposited Li metal will react with\nliquid electrolyte to form SEI continuously. Only when the SEI thickness is beyond the\ntunneling threshold, the electron transfer between Li metal and electrolyte can be\nstopped, while it is difficult to realize because the Li metal plating process is\n9\ninhomogeneous. The continuous side-reactions between Li metal and electrolyte will\nchange the composition and structure of SEI, and result in the variations of SEI modulus\naccordingly. Therefore, the unsatisfied insulation of electrons of SEI will result in\nthe continuous side-reactions between Li metal and electrolyte, inducing\nvariations of SEI modulus during continuous Li metal plating process.\nTo show the unsatisfied electrical insulation for the SEI formed on LMA, we conducted\nthe PeakForce TUNA test of AFM characterizations to show the contact current of CC1,\nMPC1, CC6 and MPC6 samples, respectively, as shown in Figure R10. The results in\nFigure R10 a, b clearly show that the SEI formed on MPC1 sample has smaller\nelectrical conductivity than that of CC1 sample, which means that the SEI formed at\nsmall current density (0.5 mA cm-2, MPC1 sample) has better electrical insulation\nproperties than the SEI formed at large current density (1 mA cm-2, CC1 sample). Even\nafter 3 mAh cm-2 of Li metal was deposited, the SEI on CC6 sample (Figure R10c) still\ndelivers higher electrical conductivity compared to that for the SEI formed on MPC6\nsample (Figure R10d). The above results clearly show that there is a significant\ndifference for the SEI on LMA when varying the current density of plating. For the SEI\nformed via small current or MPC current, it has better electrical insulation properties,\nwhich is helpful in restraining the continuous side-reactions between Li metal and\nelectrolyte. By contrast, the SEI formed via large current or CC current is less effective\nto eliminate the side-reactions between Li metal and electrolyte, which may contribute\nto its inferior cycling performance.\nUpon revision, Figure R10 has been added as Supplementary Fig. 15. The following\ncontents have also been added into our revised manuscript.\nThe PeakForce TUNA test of AFM characterizations was conducted to show the contact\ncurrent of CC1, MPC1, CC6 and MPC6 samples, respectively, as shown in\nSupplementary Fig. 15. The results clearly showed that the SEI formed on MPC1\nsample has smaller electrical conductivity than that of CC1 sample, which means that\nthe SEI formed at small current density (0.5 mA cm-2, MPC1 sample) has better\nelectrical insulation properties than the SEI formed at large current density (1 mA cm-\n2, CC1 sample). Even after 3 mAh cm-2 of Li metal was deposited, the SEI on CC6\nsample still delivers higher electrical conductivity compared to that of the SEI formed\non MPC6 sample. The above AFM characterization results clearly show that the MPC\nprotocol can enable the formation of SEI with high modulus and low electrical\nconductivity, better suppressing the formation of porous LMA.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nAgain, thank you for the insightful and important comments.\nof AFM characterizations. a, CC1 sample, b, MPC1 sample, c, CC6 sample and d,\nMPC6 sample.\n- The follow-up numerical simulation also uses the failure strain which actually is more\nimportant than Young’s modulus in mechanical failure. However, the tests cannot show\nthe failure strain.\nAuthor reply: Thank you for the valuable comments!\nFirstly, we would like to clarify that it is really a great challenge to experimentally\ncharacterize the failure of SEI, because the SEI on LMA and LMA itself is very\nsensitive to the ambient conditions. Although it has been reported that the composition\nand structure of SEI can be obtained by using cryo-TEM5,6, the failure of SEI is difficult\nto be captured. Therefore, most of the reported research are using simulation techniques\nto get the failure strain of SEI7,8.\nSecondly, in our simulations, the SEI yield strength was defined as 1% of the modulus,\nand the Von Mises criterion was used for the determination of SEI failure. Therefore,\nthe yield strength of SEI was largely determined by its modulus. And further, the\nVon Mises criterion was only used to forecast whether the SEI will be cracked, and it\nis irrelevant to the failure strain. Our results clearly show that the SEI with modulus of\n11\nprocess, which is originating from the high modulus of the SEI formed at 0.5 mA cm-2.\nOur results align well with the reported simulations that the high mechanical strength\nof SEI is capable of suppressing dendritic Li metal deposition7,8.\nWe hope the above explanation can dispel the reviewer’s concerns.\n4. Regarding COMSOL setups:\n– How sensitive are the results to assumptions about yield strength (taken as ~1% of\nYoung’s modulus)?\nAuthor reply: Thank you for raising the mechanism related comments!\nIn our model, the yield strength has been consistently assumed to be 1% of the Young's\nmodulus of SEI which was formed at different conditions. This assumption aligns well\nwith the reported researches7 and ensures that the SEI layer with higher mechanical\nstrength (e.g., 2 GPa of MPC1 sample) exhibits proportionally higher yield strength,\nwhile maintaining a constant ratio between yield stress and Young's modulus.\nConsequently, for the same applied strain, SEI layers with different Young's moduli will\nexhibit identical yielding behavior, as the yield criterion is defined by this fixed ratio.\nThe superior performance of higher-modulus SEI layers arises from their reduced strain,\na phenomenon that remains independent of the specific yield stress-to-Young's modulus\nratio employed in the parameterization.\nWe hope the above explanations can address the reviewer’s concerns.\n– Does localized variation in SEI thickness or roughness at the microscale alter these\nmacroscale conclusions?\nAuthor reply: Thank you for the insightful comments!\nThe microscale localized variations in SEI thickness or roughness do not significantly\nimpact the macroscopic conclusions of our simulations. As reported by Shen et al., the\nvariation of the ratio between the depth of defect and SEI thickness won’t significantly\nchange the optimal modulus of SEI7, which showed that the localized variation of SEI\nthickness or roughness at the microscale won’t alter the optimal SEI modulus to\nsuppress the formation of porous Li metal. In our study, Fig. 4g also clearly showed\nthat the SEI layers with different thickness and different roughness values (40 nm vs.\n50 nm) produce distinct MACD-Young's modulus curves, while the trends of these\ncurves remain highly consistent across different SEI modulus.\n5. The authors present significantly improved Coulombic efficiencies in Li‒Cu half-\n12\ncells under V vs. constant current.\n– How might similar “V” profiles be adapted for faster charge/discharge rates (beyond\n2–3 mA cm^-2)?\n– Could dynamic adjustments (e.g., real-time feedback from the voltage slope) further\noptimize the wave shape?\nAuthor reply: Thank you for the meaningful comments!\n1) Higher peak current of MPC protocol.\nAccording to our COMSOL simulation results, when the SEI modulus on 0.25 mAh\ncm-2 of Li metal is around 10 GPa and with an amplitude of 40 nm, the maximum\nallowed current density for the following 0.5 mAh cm-2 of Li metal plating can be as\nhigh as ~3.8 mA cm-2.\nFollowing the reviewer’s comments, we have carried out the electrochemical test for\nthe Li | Cu cell through MPC-3mA-3rd current (0.5 mA cm-2 (0.5 h)-1 mA cm-2 (0.5 h)-\n3 mA cm-2 (0.5 h)-0.5 mA cm-2 (1.5 h)) where the peak current at the 3rd step was 3 mA\ncm-2, as shown in Figure R11a. The CEs for the Li | Cu cell which plating Li metal via\nMPC-3mA-3rd current (Figure R11c) are obviously higher and more stable than the\ncell which plating Li metal via CC current (Figure R11b), showing the effectiveness of\nMPC protocol in increasing the cycling efficiency of LMA.\nWhen the cycling condition changed to plating 6 mAh cm-2 within 3 hours, the cycling\nperformance for the Li | Cu cell which plating Li metal via MPC-4 mA-3rd (1 mA cm-2\n(0.5 h)-2 mA cm-2 (0.5 h)-4 mA cm-2 (0.5 h)-3 mA cm-2 (0.5 h)-1 mA cm-2 (1 h)) is still\nslightly better than the cell which plating Li metal via CC-2 mA cm-2. The reason for\nthis should originate from the relatively low mechanical strength of SEI which was\nformed at 1 mA cm-2 for the MPC-4 mA-3rd current, which can only partially sustain\nthe current surge at 4 mA cm-2. Therefore, there are strong correlations for the initial\ncurrent and the peak current of MPC protocol. On the one hand, for the initial small\ncurrent density, for example, 0.1 mA cm-2, if we want to charge LMB at the shortest\ntime, we must increase the peak current to reduce the total charge time. On the other\nhand, if we want to increase the peak current of MPC protocol, reducing the initial\ncurrent density to produce SEI with high mechanical strength is necessary. The\nmechanical strength of SEI is also highly correlated with the electrolyte compositions.\nAnd therefore, the electrolyte which can produce ultra-strong SEI is capable of enabling\nfast-charging LMBs9.\n2) Dynamic control to optimize the wave shape of MPC protocol.\nfeedback from the voltage slope) further optimize the wave shape?” is yes. In this work,\nour research focuses more on disclosing the fundamentals of MPC protocol in boosting\nthe cycling performance of LMA. Actually, Wang et al. also reported a kind of “soft”\nexponential continuous differential charging (CDC) profile to increase the fast-charging\nperformance of LIBs10. The current density is:\n𝑖(𝑡) = 𝑎𝑡∙𝑒−𝑏𝑡 +𝑖 ∙𝑒−𝑐𝑡\n0\nand optimized to obtain the actual charging curve with respect to different SOC ranges,\nambient temperatures and heat dissipation coefficients. Wang’s research had proposed\nthe topology and control strategy of the simplified direct current (DC) microgrid with\nenergy storage system (ESS) and constant power load (CPL), which let us believe that\nour research has high potential to be used in the future for the performance enhancement\nof LMBs.\nUpon revision, Figure R11d, e, f has been added as Supplementary Fig. 2e, f, g,\nrespectively, in our revised SI. The following contents have also been added into our\nrevised manuscript.\nIn addition, the MPC protocol also demonstrates higher average CEs (Supplementary\nFig. 1), better cycling stability at 60 oC (Supplementary Fig. 2a), and higher CEs under\nan areal capacity of LMA of 0.3 mAh cm-2 (Supplementary Fig. 2b-d) or 6 mAh cm-2\n(Supplementary Fig. 2e-g).\nWe hope the above explanations and revisions can address the reviewer’s concerns.\ncurrent with the largest current of 3 mA cm-2 (MPC-3 mA-3rd) and the current sequence\nis 0.5 mA cm-2 (0.5 h)-1 mA cm-2 (0.5 h)-3 mA cm-2 (0.5 h)-0.5 mA cm-2 (1.5 h). b, c,\nCoulombic efficiencies (CEs) of Li | Cu cells which plating Li metal via CC-1 mA and\nMPC-3 mA-3rd protocol (as shown in Figure R15a), respectively, and then stripping Li\nmetal at constant current of 1 mA cm-2. d, e, Voltage-time and current density-time\nprofiles for the constant current of 2 mA cm-2 (CC-2 mA), and MPC current with the\nlargest current of 4 mA cm-2 (MPC-4 mA-3rd) and the current sequence is 1 mA cm-2\n(0.5 h)-2 mA cm-2 (0.5 h)-4 mA cm-2 (0.5 h)-3 mA cm-2 (0.5 h)-0.5 mA cm-2 (1 h),\nrespectively. f, Coulombic efficiencies (CEs) of Li | Cu cells which plating Li metal via\nCC-2 mA or MPC-4 mA-3rd protocols, and stripping Li metal at constant current of 2\nmA cm-2.\n6. Anode-free pouch cells were tested with partial states-of-charge (SoC).\n– In a fully charged scenario (100% SoC between 2.8 and 4.3 V for NMC), how do cycle\nlifetimes compare?\n– What is the trade-off between partial SoC operation and the practical demands for\nmaximum energy?\nAuthor reply: Thank you for the insightful comments!\n1) Comparisons for the cycle life of NMC622 | Cu cell under 100% SoC.\nDue to the complicated design of electric circuit, dynamic adjusting the charge\n15\nprotocols for the MPC charged NMC622 | Cu full cell with 100% SoC is difficult to\nrealize in our lab. Instead, we designed a constant capacity-constant voltage charge for\nboth the CC and MPC protocols, as shown in Figure R12.\nSpecifically, for the CC charge protocol, the cell was charged at 1 mA cm-2 for a fixed\ntime of 100 minutes firstly, and then it was charged at 1 mA cm-2 until the cell voltage\nreaches 4.3 V (Figure R12a). While for the MPC charge protocol, the charge protocols\nfor the 1-20 cycle and the 21-40 cycle are not the same. Typically, for the 1-20 cycle\n(Figure R12b), the cell was charged at 0.5 mA cm-2 (30 min)-1 mA cm-2 (30 min)-2 mA\ncm-2 (30 min)-1.5 mA cm-2 (30 min)-0.5 mA cm-2 (30 min) continuously, and then it\nwas charged to 4.3 V at a current of 0.5 mA cm-2; for the 21-40 cycle (Figure R12c),\nthe cell was charged at 0.5 mA cm-2 (20 min)-1 mA cm-2 (20 min)-2 mA cm-2 (20 min)-\n1.5 mA cm-2 (20 min)-0.5 mA cm-2 (20 min) continuously, and then it was charged to\n4.3 V at a current of 0.5 mA cm-2. It is worth noting that both cells were discharged at\n1 mA cm-2 to 3.5 V11, and the charging time for both the CC and MPC protocols are\nalmost the same.\nAs shown in Figure R12d-f, the cell with MPC protocol delivers better capacity\nretention compared to the cell with CC protocol, showing the advantage of our MPC\nprotocol.\n2) Trade-off between partial SoC operation and the demands for maximum energy.\nWe totally agree with the reviewer that maximum the energy density of battery is\nimportant for the practical applications. However, apart from the energy density, the\ncycling life of battery is also important for the practical applications. For example, for\nthe most recently published 500 Wh kg-1 LMBs, it could be stably cycled 130 times and\nretained 91% of its energy density12. Therefore, the total output energy density of this\ncell is around 500 Wh kg-1*130 = 65000 Wh kg-1. However, for our AFLMBs with its\ntotal energy density of 400 Wh kg-1, it can be stably cycled over 298 cycles. Even\nthough its SoC is only 80%, its total output energy density can be as high as 400 Wh\nkg-1*80%*298 = 95360 Wh kg-1, showing the advantage of our MPC protocol in\nextending the cycling life of LMBs.\nUpon revision, Figure R12 was added as Supplementary Fig.34 in our revised SI. The\nfollowing contents have also been added into our revised manuscript.\nA constant capacity-constant voltage charge for both the CC and MPC protocols was\nalso designed to approximate the dynamic 100% SoC charge of NMC622 | Cu full cells,\nas shown in Supplementary Fig. 34. The cycling results clearly show that the MPC\ncharged cell delivered better capacity retention than the CC charged cell, showing the\nadvantage of MPC protocol.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nAgain, thank you for the insightful comments.\nFigure R12. a, Constant charge protocols from 1 to 40 cycle to enable NMC622 | Cu\ncells to be charged with 100% SoC. b, c, MPC charge protocols from 1 to 20 cycle and\nfrom 20 to 40 cycle, respectively, to enable NMC622 | Cu cells to be charged with 100%\nSoC. d, e, Voltage-time curves of NMC622 | Cu cells which were charged to 100% SoC\nthrough CC and MPC protocol, respectively. f, Discharge capacity comparisons for the\nNMC622 | Cu cells which were charged to 100% SoC through CC or MPC protocol.\n7. Over-Discharge Prevention: The study shows that, after rest or calendar aging, the\n“V” protocol can re-activate dead Li to some extent.\n– Are there additional protective measures to ensure this reactivation step is consistent\nacross multiple modules in a large-scale battery?\n– Could similar approaches mitigate lithium plating issues in conventional graphite-\nanode cells at high rates?\nAuthor reply: Thank you for the constructive comments!\n17\n1) Are there additional protective measures to ensure this reactivation step is consistent\nacross multiple modules in a large-scale battery?\nWe didn’t conduct additional protective measures to ensure this reactivation step is\nconsistent across multiple modules. Nevertheless, as shown in Figure R13, 14, for either\npolycrystalline NMC622 or single crystalline NMC811 cathode materials, the cells\nwhich was charged by MPC protocol and after 2 days of calendar aging at discharge\nstate delivered higher CEs than the former cycle, demonstrating the universality for the\nreactivation step enabled by the MPC protocol. In addition, since this reactivation\nprocess was carried out at the discharge state of LMBs, where the safety concerns of\nbattery have been largely decreased compared to the battery with high SoC13, it is easy\nto reactivate the dead Li across multiple modules in a large-scale battery and without\nthe need of other protection techniques.\n2) Could similar approaches mitigate lithium plating issues in conventional graphite-\nanode cells at high rates?\nThe answer to this question is yes!\nFollowing the reviewer’s suggestions, we have further tested the fast-charging\nperformance of Li | Cu@graphite cells where the graphite anode was lithiated via CC\ncurrent or MPC current and then delithiated via CC current.\nAs shown in Figure R15c-e, the graphite anode which was lithiated via CC current of\n1C cannot be fully delithiated after only 123 cycles, which may result from the micro\nshort circuit of Li | Cu@graphite cell and shows that lithium plating issues in the\ngraphite-anode which was lithiated via CC current is serious. This can also be testified\nby the SEM images for the cycled graphite anode. As shown in Figure R16, the\nexistence of large amount of lithium inventory can be clearly observed on the surface\nof CC cycled graphite at lithiated (Figure R16a, b) or delithiated (Figure R16c, d) states,\nshowing the serous lithium plating issues during the cycling process.\nBy contrast, for the graphite anode which was lithiated via MPC current of 0.5C-1C-\n2C-1.7C-0.5C continuously, it can be stably cycled over 300 cycles (Figure R15c, e).\nIn addition, less lithium inventory can be observed according to the SEM images for\nthe MPC current cycled graphite anode whenever the graphite anode is lithiated (Figure\nR16e, f) or delithiated (Figure R16g, h). The above results clearly show that our MPC\nprotocol can not only enhance the cycling efficiency of LMA, but also enhance the\ncycling performance of graphite anode under fast-charge conditions.\nUpon revision, Figure R13, Figure R14, Figure R15 and Figure R16 has been added as\nSupplementary Fig. 38, respectively, in our revised SI. The following contents have\nalso been added into our revised manuscript.\nIt is worth noting that for polycrystalline NMC622 (Supplementary Fig. 39a, b) or\nsingle crystalline NMC811 cathode materials (Supplementary Fig. 40a, b), the above\ncapacity-recovery performances of AFLMBs can be also achieved. In addition, since\nthis reactivation process was carried out at the discharge state of LMBs, where the\nsafety concerns of battery have been largely decreased compared to the battery with\nhigh SoC13. Therefore, it is easy to reactivate the dead Li across multiple modules in a\nlarge-scale battery without the need of other protection techniques.\nThe cycling stability of graphite anode under fast-charge conditions can also be\nsignificantly increased via MPC charge protocol (Supplementary Fig. 37). The\nexistence of lithium inventory at the lithiated and de-lithiated state of cycled graphite\nanode was significantly reduced (Supplementary Fig. 38).\nWe hope the above revisions and explanations can address the reviewer’s concerns.\ncharged through a, CC and b, MPC currents, respectively. c, e, Voltage-time profiles of\nNMC622 | Cu cells aging at discharge state which was charged through CC currents.\nd, f, Voltage-time profiles of NMC622 | Cu cells aging at discharge state which was\ncharged through MPC currents.\nFigure R14. Discharge capacity and Coulombic efficiency of SCNMC811 | Cu cells\ncharged through a, CC and b, MPC currents, respectively. c, e, Voltage-time profiles of\nSCNMC811 | Cu cells aging at discharge state which was charged through CC currents.\nd, f, Voltage-time profiles of SCNMC811 | Cu cells aging at discharge state which was\ncharged through MPC currents.\ntest the fast-charging performance of CC and MPC protocols, respectively. c, Discharge\ncapacity and Coulombic efficiency of Li | graphite cells which were lithiated through\nCC or MPC protocol and delithiated at 1 mA cm-2. d, e, Voltage-capacity curves of Li |\ngraphite cells which were lithiated through CC and MPC protocol, respectively.\nFigure R16. a, b, Scanning electron microscope (SEM) images of lithiated graphite\nanode which was lithiated through CC protocol and after 50 cycles. c, d, SEM images\nof delithiated graphite anode which was lithiated through CC protocol and after 50\ncycles. e, f, SEM images of lithiated graphite anode which was lithiated through MPC\nprotocol and after 50 cycles. g, h, SEM images of delithiated graphite anode which was\nlithiated through MPC protocol and after 50 cycles.\n21\n8. High Loading Cathodes: With ~28 mg cm^-2 cathodes, the volumes of plated Li can\nbe large.\n– How do you track potential “hot spots” and localized Li depletion across the Cu\nsurface over 100+ cycles?\n– What failure mechanisms appear first at the large format level: excessive SEI\nconsumption, partial cell shorting, or cathode fatigue?\nAuthor reply: Thank you for the forward-looking comments!\n1) How do you track potential “hot spots” and localized Li depletion across the Cu\nsurface over 100+ cycles?\nThe voltage-capacity profiles of AF Li metal cells are important tools to capture the\npotential “hot spots” and localized Li depletion across the Cu surface. As shown in\nFigure R17a-c, for the NMC622 | Cu cell with CC current, there is an obvious\ndownward trend of voltage during the continuous charging process at the 50th cycle.\nThis should result from the potential “hot spots” induced micro short circuit of cell and\nwill terminate the normal cycling of LMBs quickly, which can be testified by the\ncycling performance comparisons in Figure R17a, where there is almost no capacity\ncan be discharged. For the SCNMC811 | Cu cell which was charged through CC current,\nthe same kind of micro short circuit induced by the formation of hot spots can also be\ncaptured (Figure R17d, e). By contrast, for both the NMC622 | Cu and SCNMC811 |\nCu cells, the time for the occurrence of micro short circuit can be extended via MPC\ncurrent charge, demonstrating the effectiveness of our MPC protocol in preventing the\nformation of “hot spots” and localized Li depletion.\nCurrently, we cannot operando calibrate the detailed positions which occurred the “hot\nspots” and localized Li depletion. However, the digital photos for the cycled Cu foil\nclearly show that at low pressure (Figure R18a, b) or high pressure (Figure 18c, d)\nbetween the separator and anode electrode, the most significant “hot spots” should\nlocate in the center of the cycled electrodes, where the side reactions are the most\nsignificant. And therefore, for practical applications, we should take good care of the\nedges or the defected places of large-scale LMBs, because the side-reactions at these\nplaces would be significant and these places possess high possibility to initiate the\nthermal runaway of large-scale LMBs.\n2) What failure mechanisms appear first at the large format level: excessive SEI\nconsumption, partial cell shorting, or cathode fatigue?\nWe think that the excessive SEI consumption will appear first for the failure of AF Li\n22\nmetal pouch cells. It has been reported that the electrolyte amount is the main cause for\nthe failure of LMBs14. In our research, we have also observed that there is almost no\nexistence of liquid electrolyte for the AF Li metal pouch cell which were cycled under\nboth pressure-free and high-pressure conditions (Figure R19). Although our MPC\nprotocol can effectively reduce the side-reactions in AF Li metal pouch cells, there is\nalso obvious formation of by-product layer for the cell which was cycled via MPC\nprotocol and under high-pressure conditions (Figure R19j-l). Therefore, developing\nliquid electrolytes with low reactivity against Li metal should be the core for the\npractical application of large-scale LMBs.\nHowever, for the LMBs that have enough amount of Li metal and liquid electrolyte,\nthe partial cell shorting should occur first during its failure process. We will explain this\npoint in the next comment. Currently, the keys that limit the cycling stability should be\nthe poor cycling stability of LMA, especially for the LMBs using layered oxides\ncathodes. The cycling stability of commercial layered oxide cathodes is generally\nsuperior to that of LMA, the cathode fatigue may not appear first during the failure\nprocess of LMBs.\nFigure R17. a, Discharge capacities and Coulombic efficiencies of AF Li metal coin\ncells using different charging protocols with high loading NMC622 cathodes. b, c,\nVoltage-capacity profiles of AF Li metal coin cells with high loading NMC622 cathodes\nand charged through CC and MPC currents, respectively. d, Discharge capacities and\nCoulombic efficiencies of AF Li metal coin cells using different charging protocols\nwith high loading SCNMC811 cathodes. e, f, Voltage-capacity profiles of AF Li metal\ncoin cells with high loading SCNMC811 cathodes and charged through CC and MPC\n23\ncurrents, respectively.\nFigure R18. a, b, Digital photos of Cu electrode after 10 cycles which was protected\nby 200 μm PTFE in Li | Cu cell and through CC and MPC protocol, respectively. c, d,\nDigital photos of Cu electrode after 50 cycles in Li | Cu cell and through CC and MPC\nprotocol, respectively.\nseparator of the AF Li metal pouch cell tested at pressure-free condition and through\nCC charge protocol. d, e, f, Digital photos, front and cross-sectional SEM images for\nthe cycled separator of the AF Li metal pouch cell tested at pressure-free condition and\nthrough MPC charge protocol. g, h, i, Digital photos, front and cross-sectional SEM\nimages for the cycled separator of the AF Li metal pouch cell tested at high-pressure\ncondition and through CC charge protocol. j, k, l, Digital photos, front and cross-\nsectional SEM images for the cycled separator of the AF Li metal pouch cell tested at\nhigh-pressure condition and through MPC charge protocol.\n9. The authors present cross-sectional SEM images of used electrodes and separators.\n– In the event of micro-cracks or short-circuits, does the volcano protocol fail abruptly\nor gradually?\n– Would in situ tomography (e.g., synchrotron X-ray or neutron imaging) capture these\nmorphological changes more completely?\nAuthor reply: Thank you for the insightful comments!\n1) In the event of micro-cracks or short-circuits, does the volcano protocol fail abruptly\nor gradually?\nLMBs. As shown in Figure R20a-c, for both cycling protocols of CC or MPC, the cell\ncan still be operated continuously even though the terminated charge voltage of\nAFLMBs with NMC622 cathode has reached 5 V vs. Li+/Li. This clearly show that the\nAFLMBs will fail gradually during the continuous cycling process. However, for the\nLMBs with N/P ratio of ~0.5 (Figure R20d-f), the cell with CC protocol exhibited an\nabrupt failure after its terminated charge voltage reached 5 V vs. Li+/Li, while the cell\nthat was cycled via MPC protocol exhibited a gradual failure.\nThe reason for the difference of failure modes between AFLMBs and LMBs should\noriginate from the difference of Li metal capacity. For the low capacity of active Li\nmetal, the Li metal anode in AFLMBs will be corroded quickly, thus its cycling life will\nbe shorter than LMBs. The short cycle life of AFLMBs lies in its thinner by-product\nlayer, which may be incapable of piercing through polymer separator and incur battery\nshort-circuit. For LMBs, although its life will be longer, the accumulated by-product\nlayer on the surface of LMA will be more significant than that in AFLMBs, which may\nincur the short-circuit of LMBs and result in the abrupt failure of LMBs eventually.\n2) Would in situ tomography (e.g., synchrotron X-ray or neutron imaging) capture these\nmorphological changes more completely?\nThank you for the constructive comments! It has been reported that neutron imaging\ncan help capture the morphological changes of LMA more clearly15. Unfortunately, we\ncurrently do not have access to these techniques. Thus, we cannot provide the in-situ\ntomography results (e.g., synchrotron or neutron imaging) to show you more\nfundamental details about the advantages of our MPC protocol compared with C\nprotocol. Your suggestions are very valuable for us to develop in situ imaging\ntechniques to understand lithium plating/stripping in lithium metal batteries in the\nfuture.\nUpon revision, Figure R20b, c, e, f has been added as Supplementary Fig. 47a, b, c, d,\nrespectively in our revised SI. The following contents have also been added into our\nrevised manuscript.\nThe failure mechanism of AFLMBs and LMBs which was charged via CC current was\ndifferent. As shown in Supplementary Fig. 47a, b, for both cycling protocols of CC or\nMPC, the AFLMBs can still be operated continuously even though the terminated\ncharge voltage has reached 5 V vs. Li+/Li. This clearly show that the AFLMBs will fail\ngradually during the continuous cycling process. However, for the LMBs with N/P ratio\nof ~0.5 (Supplementary Fig. 47c, d), the cell with CC protocol exhibited an abrupt\nfailure after its terminated charge voltage reached 5 V vs. Li+/Li, while the LMB cell\nwith MPC protocol exhibited a gradual failure mechanism. The reason for the\ndifference of failure modes between CC charged AFLMBs and LMBs should originate\nfrom the difference of Li metal capacity. For the low capacity of active Li metal, the\nLMA in AFLMBs will be corroded quickly, thus its cycling life will be shorter than that\nof LMBs. The short cycle life of AFLMBs lies in its thinner by-product layer, which may\nbe incapable of piercing through polymer separator and incur battery short-circuit. For\nLMBs, although its life will be longer, the accumulated by-product layer on the surface\nof LMA will be more significant than that in AFLMBs, which may incur the short-circuit\nof LMBs and result in the abrupt failure of LMBs eventually.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nFigure R20. a, Discharge capacities and Coulombic efficiencies of NMC622 | Cu cells\nusing different charging protocols. b, c, Voltage-time curves of NMC622 | Cu cells\nwhich were charged through CC and MPC protocol, respectively. d, Discharge\ncapacities and Coulombic efficiencies of NMC622 | Li cells using different charging\nprotocols. e, f, Voltage-time curves of NMC622 | Li cells which were charged through\nCC and MPC protocol, respectively.\nThe authors propose a potential-varying charge profile to alter and improve lithium\nmetal deposition for anode-free lithium metal batteries. Specifically, their proposed\ncurrent rates start small, peak in the middle of the charge step, and end small. They\npropose that the voltage-varying protocol leads to a higher strength SEI that is more\nrate capable. The results are interesting, but I have some critiques on the proposed\nmechanism and presented data.\nAuthor reply: We thank the reviewer for your positive and constructive comments on\nour manuscript. Following your comments, we have made significant revisions on our\nmanuscript to improve its quality. A point-by-point response is listed as follows:\n1. Overall, the manuscript was a bit difficult to parse because there are too many\nreferenced supplementary figures, and I would recommend somehow highlighting or\nconsolidating the most important figures that make the authors’ point. Even though I\nhave both the SI and the main opened up at the same time, it takes a while to go back\nand forth and view every single SI figure. There are many parameters explored, and\nsome I am not sure have a big impact. For example, does a temperature difference of\n1.5degC briefly at the beginning of the discharge step really have that big of an impact\n(SI Figure 37)?\nAuthor reply: Thank you for the constructive comments!\n1) Highlighting or consolidating the most important figures.\nFollowing the reviewer’s comments, we have consolidated the most important figures\nin supplementary information to make our article more concise for the reviewers and\nreaders.\n2) Does a temperature difference of 1.5degC briefly at the beginning of the discharge\nstep really have that big of an impact (SI Figure 37)?\nWe would like to clarify that the temperature difference of 1.5 oC during the first\ndischarge process was captured on the AF Li metal pouch cell with capacity of 1.5 Ah\nonly. It has been reported that the large charge current16 or large discharge current17 of\nLIBs will produce more heat during of LIBs, while the heat phenomena during the\ndischarge process of LIBs which was induced by varying the charge current has\nbeen rarely reported. In our research, we captured that our MPC protocol will cause\na temperature rise of ~0.5 oC during the charge process of AF Li metal pouch cell\ncompared to the CC charged cell, while compared to the MPC charged cell, the cell\nwith CC protocol delivered a temperature rise of ~1.5 oC at the beginning of discharge\n28\nprocess. The above results clearly show that the MPC protocol charged AF Li metal\ncell has less side-reactions happened during the discharge process, which agrees well\nwith the SEM results obtained from Figure R19.\nTherefore, on the one hand, although the temperature difference of 1.5 oC seems small,\nit represents a unique and significant progress compared to the reported research. On\nthe other hand, the temperature difference of 1.5 oC was captured only on the first cycle\nof single AF Li metal pouch cell, and when it comes to the large-scale battery module,\nthe temperature difference will be larger and the accompanied safety concerns will be\nmore serious. Especially for the cycled AF Li metal pouch cells, where the accumulated\nby-product layer is very thick. In this occasion, even tiny temperature rise of cells may\nignite the combustible organic lithium compounds and cause the thermal runaway of\ncell eventually.\nWe hope the above explanations can address the reviewer’s concerns. Again, thank you\nfor the constructive comments.\n2. The difference in measured modulus from AFM is one of the author’s main arguments\nfor why they see performance improvements. However, the AFM only captures a very\nsmall section of the electrode, and we have to assume that it is representative of the\nentire electrode. What is the variation in modulus across different parts of the electrode?\nAuthor reply: Thank you for the insightful comments!\nWe totally agree with the reviewer’s points that our main arguments come from the\ndifference in measured modulus from AFM characterizations. To reduce the accidental\nerrors of modulus test which may be caused by the position variations of electrodes, we\nconducted the modulus tests at three positions of LMA totally, as shown in Figure R21a.\nThe detailed Young’s modulus distribution maps were shown in Figure R22 and the\nexact value of modulus of different samples and at different positions were compared\nin Figure R21b. It is worth noting that in our previous submission, our comparisons of\nmodulus and simulations were based on the modulus results obtained in the position 2\nof different samples, which is, 1.1 GPa for CC1 sample, 2.1 GPa for MPC1 sample, 2.8\nGPa for CC6 sample and 5.3 GPa for MPC6 sample, respectively.\nAlthough the modulus of SEI will change when the positions are varied, the averaged\nvalues of MPC1 sample (2.3 GPa) and MPC6 sample (4.9 GPa) are still significantly\nhigher than that of CC1 sample (1 GPa) and CC6 sample (2.5 GPa), respectively,\ndemonstrating the advantage of our MPC protocol in forming SEI with high mechanical\nstrength. One interesting thing is that the highest modulus of CC6 and MPC6 sample\nwere both captured at position 2, which shows that for the LMA which has high capacity,\nthe modulus test at the position 2 (i.e., the central area) of the electrode will better reflect\nthe real value of SEI on the surface of LMA.\nUpon revisions, Figure R21 and Figure R22 has been added as Supplementary Fig. 11\nand Supplementary Fig. 12, respectively, in our revised SI. The following contents have\nalso been added into our revised manuscript.\nTo reduce the accidental errors of modulus test which may be caused by the position\nvariations of electrodes, we have conducted the modulus tests at three positions of LMA\ntotally, as shown in Supplementary Fig. 11a. When we choose the test results at position\n2 (i.e., the central area of electrode) of different samples to make comparison, the\nYoung’s modulus of the initial SEI (with Li capacity of 0.25 mAh cm-2) at 1 mA cm-2 at\nCC1 (1.1 GPa, Fig. 2l) is lower than that formed at 0.5 mA cm-2 at MPC1 (2.1 GPa,\nFig. 2n).\nAlthough the modulus of SEI will change the positions are varied, the averaged values\nof MPC1 sample (2.3 GPa) and MPC6 sample (4.9 GPa) are still significantly higher\nthan that of CC1 sample (1 GPa) and CC6 sample (2.5 GPa), respectively,\ndemonstrating the advantage of our MPC protocol in forming SEI with high mechanical\nstrength (Supplementary Fig. 11b and Supplementary Fig. 12). When the plated Li\nmetal was fully stripped, the tested modulus of MPC1 sample is also higher than that\nof CC1 sample (Supplementary Fig. 13), aligns well with the above modulus analysis.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nFigure R21. a, Schematic showing the positions of samples which were used to conduct\nAFM characterizations. b, Comparisons for the Young’s modulus of SEI on different\nsamples.\nvalue of each sample) on the surface of CC1 sample. d, e, f, Young’s modulus\ndistribution maps (the inset number is the mean value of each sample) on the surface of\nMPC1 sample. g, h, i, Young’s modulus distribution maps (the inset number is the mean\nvalue of each sample) on the surface of CC6 sample. j, k, l, Young’s modulus\ndistribution maps (the inset number is the mean value of each sample) on the surface of\n3. While the authors show some reproducibility in Figure 1, it would be more\ncompelling if the authors can show the spread of their results in Figure 5 and 6. It\nappears that in many of the cases in Figures 5-6, cell failure occurs rapidly and within\njust 1 or 2 cycles. This is often indicative of electrolyte dry out. On the other hand, the\ncells in Figure 1 show more gradual capacity fade, indicating gradual passivation and\nSEI growth.\nAuthor reply: Thank you for the constructive comments!\n1) Spread of results in Figure 5 and Figure 6.\nWe totally agree with the reviewer that the spreading for the cycling performances of\nfull cells such as AF Li metal coin cells or AF Li metal pouch cells will be more\ncompelling than the spreading of Li | Cu half cells. As shown in Figures R13, R14, R23\nand R24, all the cycling performances of both the AF Li metal coin cells and AF Li\nmetal pouch cells that we have reported in our previous submission can be spread. In\nour previous submission, for the reason of consolidating our results, we didn’t present\nthe repeat test of AF Li metal coin cells and AF Li metal pouch cells. We hope the above\nresults can address the reviewer’s concerns.\n2) Comparison for the failure mechanism of AFLMBs and LMBs.\nThe failure mechanism of LMBs is highly correlated with the amount of Li metal\ncapacity in LMBs, i.e., the N/P ratio of LMBs. As shown in Figure R20a-c, for both\ncycling protocols of CC and MPC, the AFLMBs can still be operated continuously even\nthough the terminated charge voltage has reached 5 V vs. Li+/Li. This clearly show that\nthe AFLMBs will fail gradually during the continuous cycling process. However, for\nthe LMBs with N/P ratio of ~0.5 (Figure R20d-f), the cell with CC protocol exhibited\nan abrupt failure after its terminated charge voltage reached 5 V vs. Li+/Li, while the\nLMB cell with MPC protocol exhibited a gradual failure mechanism.\nThe reason for the difference of failure modes between the AFLMBs and the LMBs\nshould originate from the difference of Li metal capacity. For the low capacity of active\nLi metal, the Li metal anode in AFLMBs will be corroded quickly, thus its cycling life\nwill be shorter than LMBs. The short cycle life of AFLMBs lies in its thinner by-product\nlayer, which may be incapable of piercing through polymer separator and incur battery\nshort-circuit. For LMBs which was charged through CC protocol, although their life\nwill be longer, the accumulated by-product layer on the surface of LMA will be more\n32\nsignificant than that in AFLMBs, which may incur the short-circuit of LMBs and result\nin the abrupt failure of LMBs eventually.\nUpon revision, Figure R23a, Figure R23b, Figure R13, Figure R14, Figure R24 and\nFigure R20b, c, e, f has been added as Fig. 5c, Fig.5d, Supplementary Fig. 39,\nSupplementary Fig. 40, Fig. 6e and Supplementary Fig. 47a, b, c, d, respectively, in our\nrevised manuscript and SI. The following contents have also been added into the\ncontexts of our revised manuscript.\nIt is worth noting that for both polycrystalline NMC622 (Supplementary Fig. 39a, b) or\nsingle crystalline NMC811 cathode materials (Supplementary Fig. 40a, b), the above\ncapacity-recovery performances of AFLMBs can be also achieved. In addition, since\nthis reactivation process was carried out at the discharge state of LMBs, where the\nsafety concerns of battery have been largely decreased compared to the battery with\nhigh SoC13. Therefore, it is easy to reactivate the dead Li across multiple modules in a\nlarge-scale battery without the need of other protection techniques.\nThe failure mechanism of AFLMBs and LMBs which was charged via CC current was\ndifferent. As shown in Supplementary Fig. 47a, b, for both cycling protocols of CC or\nMPC, the AFLMBs can still be operated continuously even though the terminated\ncharge voltage has reached 5 V vs. Li+/Li. This clearly show that the AFLMBs will fail\ngradually during the continuous cycling process. However, for the LMBs with N/P ratio\nof ~0.5 (Supplementary Fig. 47c, d), the cell with CC protocol exhibited an abrupt\nfailure after its terminated charge voltage reached 5 V vs. Li+/Li, while the LMB cells\nwith MPC protocol exhibited a gradual failure mechanism. The reason for the\ndifference of failure modes between CC charged AFLMBs and LMBs should originate\nfrom the difference of Li metal capacity. For the low capacity of active Li metal, the\nLMA in AFLMBs will be corroded quickly, thus its cycling life will be shorter than that\nof LMBs. The short cycle life of AFLMBs lies in its thinner by-product layer, which may\nbe incapable of piercing through polymer separator and incur battery short-circuit. For\nLMBs, although their life will be longer, the accumulated by-product layer on the\nsurface of LMA will be more significant than that in AFLMBs, which may incur the\nshort-circuit of LMBs and result in the abrupt failure of LMBs eventually.\nusing different charging protocols with high loading a, NMC622 cathodes and b,\nSCNMC811 cathodes respectively.\nFigure R13. Discharge capacity and Coulombic efficiency of NMC622 | Cu cells\ncharged through a, CC and b, MPC currents, respectively. c, e, Voltage-time profiles of\nNMC622 | Cu cells aging at discharge state which was charged through CC currents.\nd, f, Voltage-time profiles of NMC622 | Cu cells aging at discharge state which was\ncharged through MPC currents.\ncharged through a, CC and b, MPC currents, respectively. c, e, Voltage-time profiles of\nSCNMC811 | Cu cells aging at discharge state which was charged through CC currents.\nd, f, Voltage-time profiles of SCNMC811 | Cu cells aging at discharge state which was\ncharged through MPC currents.\ncell tested under high-pressure conditions with CC and MPC protocols, the electrolyte\nhere is 2M LiDFOB and 1.4M LiBF in FEC/DEC (v/v, 1/2).\nusing different charging protocols. b, c, Voltage-time curves of NMC622 | Cu cells\nwhich were charged through CC and MPC protocol, respectively. d, Discharge\ncapacities and Coulombic efficiencies of NMC622 | Li cells using different charging\nprotocols. e, f, Voltage-time curves of NMC622 | Li cells which were charged through\nCC and MPC protocol, respectively.\n4. I was confused why the pouch cells in Fig 6 were cycled in a different protocol than\nthe other cells. Why do subsequent cycles undergo less charge capacity (why is the\ndischarge capacity decreased from 1.5 to 1.2 Ah and then to 0.9 Ah?)\nAuthor reply: Thank you for the insightful comments!\n1) Reasons for the decreased discharge capacity from 1.5 to 1.2 Ah and then to 0.9 Ah\nof our AF Li metal pouch cells.\nThe MPC protocol can vary by adjusting the charging time of each step, while we\ncannot charge LMBs with 100% SoC in every cycle, i.e., we cannot precisely adjust the\ncharge time of each step to realize the 100% SoC at the end of MPC charge of every\ncycle. One possible method to tackle this problem is to adjust the charge time of each\nstep before the charge step of next cycle and based on the discharge capacity of previous\ncycle, while this will sacrifice the charge convenience of LMBs significantly. Therefore,\n36\nwe proposed a gradient charge protocol (1.5 Ah-1.2 Ah-0.9 Ah) to implement the\npractical applications of MPC charge protocol in LMBs.\n2) Comparisons for the cycle life of NMC622 | Cu cell under 100% SoC.\nDue to the complicated design of electric circuit, dynamic adjusting the charge\nprotocols for the MPC charged NMC622 | Cu full cell with 100% SoC is hard to realize\nin our lab. Instead, we designed a constant capacity-constant voltage charge for both\nthe CC and MPC protocols, as shown in Figure R12.\nSpecifically, for the CC charge protocol, the cell was charged at 1 mA cm-2 for a fixed\ntime of 100 minutes firstly, and then it was charged at 1 mA cm-2 until the cell voltage\nreaches 4.3 V (Figure R12a). While for the MPC charge protocol, the charge protocols\nfor the 1-20 cycle and the 21-40 cycle are not the same. Typically, for the 1-20 cycle\n(Figure R12b), the cell was charged at 0.5 mA cm-2 (30 min)-1 mA cm-2 (30 min)-2 mA\ncm-2 (30 min)-1.5 mA cm-2 (30 min)-0.5 mA cm-2 (30 min) continuously, and then it\nwas charged to 4.3 V at a current of 0.5 mA cm-2; for the 21-40 cycle (Figure R12c),\nthe cell was charged at 0.5 mA cm-2 (20 min)-1 mA cm-2 (20 min)-2 mA cm-2 (20 min)-\n1.5 mA cm-2 (20 min)-0.5 mA cm-2 (20 min) continuously, and then it was charged to\n4.3 V at a current of 0.5 mA cm-2. It is worth noting that both cells were discharged at\n1 mA cm-2 to 3.5 V11, and the charging time for both the CC and MPC protocols are\nalmost the same.\nAs shown in Figure R12d-f, the cell with MPC protocol delivers better capacity\nretention and relatively higher Coulombic efficiency compared to the cell with CC\nprotocol, showing the advantage of our MPC protocol.\n3) Future development of V protocol.\nOur research focuses more on disclosing the fundamentals of MPC protocol in boosting\nthe cycling performance of LMA. Actually, Wang et al. also reported a kind of “soft”\nexponential continuous differential charging (CDC) profile to increase the fast-charging\nperformance of LIBs10. The current density is:\n𝑖(𝑡) = 𝑎𝑡∙𝑒−𝑏𝑡 +𝑖 ∙𝑒−𝑐𝑡\n0\nand optimized to obtain the actual charging curve with respect to different SOC ranges,\nambient temperatures and heat dissipation coefficients. Wang’s research had proposed\nthe topology and control strategy of the simplified direct current (DC) microgrid with\nenergy storage system (ESS) and constant power load (CPL), which let us believe that\nour research has high potential to be used in the future for the performance enhancement\nof LMBs.\nUpon revision, Figure R12 was added as Supplementary Fig.34 in our revised SI. The\nfollowing contents have also been added into our revised manuscript.\nA constant capacity-constant voltage charge for both the CC and MPC protocols were\nalso designed to approximate the dynamic 100% SoC charge of NMC622 | Cu full cells,\nas shown in Supplementary Fig. 34. The cycling results clearly show that the MPC\ncharged cell delivered better capacity retention than the CC charged cell, showing the\nadvantage of MPC protocol.\nWe hope the above revisions and explanations can address the reviewer’s concerns.\nAgain, thank you for the insightful comments.\nFigure R12. a, Constant charge protocols from 1 to 40 cycle to enable NMC622 | Cu\ncells to be charged with 100% SoC. b, c, MPC charge protocols from 1 to 20 cycle and\nfrom 20 to 40 cycle, respectively, to enable NMC622 | Cu cells to be charged with 100%\nSoC. d, e, Voltage-time curves of NMC622 | Cu cells which were charged to 100% SoC\nthrough CC and MPC protocol, respectively. f, Discharge capacity comparisons for the\nNMC622 | Cu cells which were charged to 100% SoC through CC or MPC protocol.\n38\n5. The authors conclude that the “SEI rupture is captured to happen..” (line 339) but\nrupturing is not presented anywhere in the manuscript and there is no physical evidence\nof SEI rupturing.\nAuthor reply: Thank you for these suggestive comments!\nUpon revision, the following contents have been added into our revised manuscript.\nThe formation of porous Li metal anode (LMA) was captured to happen upon\ncontinuous traditional constant (CC) current charge of LMA (Fig. 2a-d and\nSupplementary Fig. 7), leading to porous Li metal structure with large surface area.\nThe authors discuss alternate Li plating protocols to achieve more dense and more\nuniform metallic Li-films.\nPlease consider to not call this a volcano like shape but rather V shaped protocol\nbecause a) it will be confusing for people from the field of catalysis and b) this is an\ninverted volcano ... a crater? => better call it V-shaped or crater shaped if you like.\nActually looks like a excavator made crater.\nAuthor reply: We thank the reviewer for their constructive comments on our manuscript.\nFollowing your comments, we have carried out new experiments to address your\nconcerns. Upon revision, we have made significant revisions on our manuscript to\nimprove its quality. A point-by-point response is listed as follows:\nFirstly, we sincerely apologize for the errors that we made in the figures and contexts\nin our previous submission, and we also sincerely thank the kindly reminding from the\nreviewer!\nUpon revisions, we have changed the “Volcano-curved stepwise current” to be “Middle\npeaked current”, which is abbreviated as “MPC” (Figure R25c, d, f, h). In the meantime,\nthe “Constant current” was also abbreviated as “CC” (Figure R25a, b, e, g).\nWe hope the above revisions can address the reviewer’s concerns.\nFigure R25. a, c, Voltage-capacity and current density-capacity profiles for the\ntraditional constant (CC) and middle peak (MPC) plating mechanisms in Li | Cu cells,\nrespectively. b, d, Current density-time profiles for the CC and MPC plating\nmechanisms in Li | Cu cells, respectively. e, f, Charge-discharge voltage-time profiles\nof AF Li metal coin cells coupled with high loading NMC622 cathodes at the second\ncycle charged through CC and MPC protocols, respectively. g, h, The 1st cycle charge-\n40\ndischarge voltage-time profiles of 1.8 Ah AF Li metal pouch cells tested at high-\npressure conditions, which was charged through CC and MPC protocol, respectively,\nand then discharged with constant protocol at 0. 3A.\n1. There has been a lot of work on metallic anodes in liquid and solid state electrolytes\nand most of that work is not properly discussed and as such the manuscript lacks behind\nwhat it could offer as insight for the community.\nThere is great work from Axel Groß that discusses barrier height as a reason for\ndendrite growth in Li and Na but the absence in Mg and Ca. There is also work by the\nentire community of electroplaters that lead to the design of a pulsed protocol by\nWolfgang Schuhmanns group that showed that it is possibile to exceed 6000 cycles for\na metallic anode. There is also work on non-linear charging protocols by soem authors\nthat show differences. As I understand growth of thin films we have an incoming ion\nenergy (usually low here), surface diffusion and bulk diffusion. Initially the authors\nobserve a very low potential vs. Li/Li+ and then a levelling off at lower potentials for\nthe constant case. This looks to me that as long as there is no improper seed or if the\nseeds were destroyed the effect would be the same. Can the authors maybe perform an\nexperiment of a constant current charging for like 0.3 mAh/cm2 then make a short same\ncurrent reverse pulse of the same current density of 0.05 mA/cm2 and then continue\ncharging normally? This would then allow a better discussion.\nAuthor reply: Thank you for the constructive comments!\n1) In-depth discussion of related work on metallic anodes.\nWe sincerely apologize for missing the discussions for the self-diffusion height as\nreason for Li dendrite growth reported by Axel Groß et al.18, the formation of\nhomogeneous Li metal anode enabled by pulsed current which was reported by\nWolfgang Schuhmann et al.19 and the simulated non-linear potentiodynamic battery\ncharging protocols reported by Stein20. We have cited these references and added more\nrelevant discussions.\n2) MPC protocol enabled stable cycling of LMA with low capacity of 0.3 mAh cm-2.\nFollowing the reviewer’s suggestions, we have carried out the electrochemical tests of\nLi | Cu cells where the plating capacity of LMA is 0.3 mAh cm-2, the plating time is 3\nhours and the stripping current of LMA is 0.1 mA cm-2. For the CC plated LMA, a\ncontinuous current of 0.1 mA cm-2 was applied (Figure R26a). For the MPC plated\nLMA, a sequentially 0.05 mA cm-2 (0.5 h)-0.1 mA cm-2 (0.5 h)-0.2 mA cm-2 (0.5 h)-\n0.15 mA cm-2 (0.5 h)-0.05 mA cm-2 (1 h) current was applied to plate Li metal on Cu\n(Figure R26b). The cycling performances in Figure R26c, d show that the LMA with\nshowing its effectiveness in stabilizing LMA. It is worth noting that the LMA with CC\ncurrent can also demonstrate a high average Coulombic efficiency of 97.7% within 100\ncycles. The above results clearly show that even though both the plating capacity (0.3\nmAh cm-2) and plating current (0.1 mA cm-2) are already very small, reducing the\nstarting and ending current whereas increasing the middle current is still effective in\nproviding LMA with higher cycling efficiency.\n3) Li metal nucleation and Li ion diffusivity analysis.\nFor LMA, apart from the nucleation seeds, the Li ion diffusivity of SEI is also very\nimportant for uniform Li metal deposition. As reported by Biswal et al.21, a higher Li\nion diffusivity in SEI means faster 2D migration of Li ions, which promotes more\nspread-out/delocalized electrodeposition. Because of the fast reduction kinetics of Li-\nions at the electrode, a high Li ion diffusivity in SEI would also decrease the Li ion\nconcentration gradient in the SEI. Synergistically, high surface diffusivity and high\ninterfacial energy of SEI would facilitate planar electrodeposition. On the other hand,\nthe SEI lacking such interfacial advantages will form a 3D, bloblike nuclei that have a\nhigh probability of succumbing to the morphological instability leading to the growth\nof mossy/dendritic Li electrodeposition. We never doubt the functions of nucleation\nseeds for uniform Li metal deposition22-24. However, the dispersion of seeds is also very\nimportant for the following uniform Li metal plating, and the homogeneous dispersion\nof nucleation seeds necessitate the adoption of ultrahigh current, which may sacrifice\nthe practicability of LMBs (as shown in Supplementary Tab. 6 in our revised SI).\nTherefore, our focus is to adjust the current distribution of charge protocol within a\ncertain current limit without prolonging its charging time to realize the best LMBs.\nUpon revision, Figure R26a, b, d has been added as Supplementary Fig. 2b, c, d,\nrespectively, in our revised SI. The following contents have also been added into our\nrevised manuscript.\nHowever, for the high self-diffusion barriers of Li adatom to form Li nuclei18 and the\ninsufficient Li+ ion conductivities and mechanical strength of the solid electrolyte\ninterphase (SEI) on LMA1, the dendritic LMA will be formed during the charge process\nof LMBs.\nBesides, various charge protocols have been proposed to increase the cycling\nperformance of lithium battery, for example, the pulsed current19,25, the asymmetric\nbidirectional current 26, the two-step current27, the self-heat current28, the initially\n42\nultrahigh current seeded Li metal growth23,24 and the simulated non-linear\npotentiodynamic battery charging protocols20, and so on. Some of them have shown\nsuccess in industrial applications, while the underlying role of different charge\nprotocols for LMBs remain poorly understood.\nIn addition, the MPC protocol also demonstrates higher average CEs (Supplementary\nFig. 1), better cycling stability when the cycling temperature is 60 oC (Supplementary\nFig. 2a), and higher CEs whatever the capacity of LMA is 0.3 mAh cm-2 (Supplementary\nFig. 2b-d) or 6 mAh cm-2 (Supplementary Fig. 2e-g).\nWe hope the above revisions can address the reviewer’s concerns.\nFigure R26. a, b, Voltage-time and current density-time profiles for the CC current of\n0.1 mA cm-2 (CC-0.1 mA), and MPC plating current with the largest current of 0.2 mA\ncm-2 (MPC-0.2 mA-3rd) and the current sequence is 0.05 mA cm-2 (0.5 h)-0.1 mA cm-\n2 (0.5 h)-0.2 mA cm-2 (0.5 h)-0.15 mA cm-2 (0.5 h)-0.05 mA cm-2 (1 h), respectively. c,\nd, Coulombic efficiencies (CEs) of Li | Cu cells which plating Li metal via CC-0.1 mA\nor MPC-0.2 mA-3rd protocols, and stripping Li metal at constant current of 0.1 mA cm-\n2.\n2. The morphology in some figures look a lot like for a thompson structure zone diagram.\nconsider discussing it in this context.\nAuthor reply: Thank you for the suggestive comments!\nFollowing the reviewer’s suggestions, we have carried out a literature survey to learn\nthe Thompson structure zone diagram. And we found that there are some similarities\nbetween the Li metal morphologies that we have captured and the Thompson structure.\nTypically, as reported by Thornton29, the film coatings can be represented as a function\n43\nof T/T in terms of the three zones. As shown in Figure R27, the “Zone 1” (T/T <0.3)\nm m\nconsists of tapered crystals with domed tops which are separated by voided boundaries.\nThe “Zone 2” (0.3<T/T <0.5) consists of columnar grains separated by distinct dense,\nm\nintercrystalline boundaries, and its surface has a smooth and mat appearance. The\n“Zone 3” (0.5<T/T <1) consists of equiaxed grains with a bright surface. Generally, it\nm\nis highly preferred to form a dense barrier layer coating. And therefore, the “Zone 3”\nstructure is highly favored for the thin film growth, while growth of Zone 1 structures\nshould be suppressed as much as possible.\nUpon revision, the following discussions have been added into our revised manuscript.\nWhen the Li capacity increases to 3 mAh cm-2 (theoretical thickness of ~12.9 μm),\nthe\nLi metal deposited through CC protocol exhibits a porous “Zone 1” like structure (Fig.\n2c) and delivers a thickness of 16.7 μm (Fig. 2d), which corresponds to a porosity of\n22.9% and should be avoided for film growth29. Conversely, for the 3 mAh cm-2 of Li\nmetal which was formed by MPC protocol, it exhibits much dense “Zone 3” like\nstructure (Fig. 2g) with a thickness of only 13.6 μm (Fig. 2h), which corresponds to a\nporosity of 5.4% only.\nFigure Redacted\nFigure R27. Structure zone diagram proposed by Thornton29.\n3. Dendrite and island growth and so on depend on curvature which is not discussed.\nYoungs modulus will depend on defect density. This is not discussed.\ndeformation. Please add a discussion of curvature, surface diffusion in context to\ndeposition rate.\nAuthor reply: Thank you for the insightful comments!\nFollowing the reviewer’s suggestions, we have added relevant discussions of curvature\nand surface diffusion (ionic conductivity of SEI) in context to deposition rate in our\nrevised manuscript.\nUpon revision, the following contents have been added into our revised manuscript.\nHowever, for the high self-diffusion barriers of Li adatom to form Li nuclei18 and the\ninsufficient Li+ ion conductivities and mechanical strength of the solid electrolyte\ninterphase (SEI) on LMA1, the dendritic LMA will be formed during the charge process\nof LMBs. The irregular surface curvature of LMA will also boost the formation of Li\ndendrites and the high charge current will accelerate this process30.\n4. In the introduction authors state that \"battery performance significantly varies with\ncharging and discharging protocols\" I believe this warrants a bit of discussion. Some\ntesting protocols are designed to measure performance but I think few tests are designed\nwith degrading performance (except abusive tests) such that I think some additional\ndiscussion should be done here.\nAuthor reply: Thank you for your suggestion!\nFollowing the reviewer’s comments, we have rephrased this sentence to a new sentence\nwhich can better represent the works which have been carried out by other scientists.\nUpon revision, the following contents have been added to replace the sentence “battery\nperformance significantly varies with charging and discharging protocols”.\nThe cycling performance of traditional LIBs can be increased by using many advanced\ncycling protocols, especially under the fast-charging conditions10,31,32. For LMBs, the\ncharge/discharge current represent the plating/dissolution rate of LMA, respectively. It\nhas been reported that the small charge current is helpful in boosting the reversibility\nof LMA33,34, the small discharge current of LMBs can boost the void-free Li metal\ndissolution35, and their relative values will also influence the cycling performances of\nLMBs36.\nBesides, various charge protocols have been proposed to increase the cycling\nperformance of lithium battery, for example, the pulsed current19,25, the asymmetric\nbidirectional current 26, the two-step current27, the self-heat current28, the initially\n45\nultrahigh current seeded Li metal growth23,24 and the simulated non-linear\npotentiodynamic battery charging protocols20, and so on. Some of them have shown\nsuccess in industrial applications, while the underlying role of different charge\nprotocols for LMBs remain poorly understood.\n4. \"generally in a 62 “stressed” state,\" I understand that this is referring to thin film\nstress but maybe explain a bit what this means to the not knowing audience. Consider\nadding the citations at the end of the sentence as it looks like strange Sn and Cu isotopes.\nAuthor reply: Thank you for the suggestive and important comments!\nFollowing the reviewer’s suggestions, we have changed the positions of the citations to\navoid the potential misunderstandings from both the reviewers and readers.\nUpon revision, the following sentence have been added in our revised manuscript to\nbetter describe the wide-spread existence of stress in thin films.\nThe electrochemical deposition of thin films on the substrates are generally in a\n“stressed” state, for example, Sn and Cu thin films37,38.\n5. minor rephrasing remarks:\nIn figure 1 and throughout the manuscript please consider rephrasing \"V current\"\nand \"C current\".\nthe previous abandoned choice -> should be rephrased\nAuthor reply: Thank you for the nice suggestions!\n1) Rephrasing “V current” and “C current”.\nWe sincerely thank the kindly reminding from the reviewer! We have changed the\n“Volcano-curved stepwise current” to be “Middle peaked current”, which is abbreviated\nas “MPC”. In the meantime, the “Constant current” was also abbreviated as “CC”. We\nhope the above revisions can address the reviewer’s concerns.\n2) Rephrasing “the previous abandoned choice”\nTo avoid this mistake, we have deleted this phrase and the same sentence has been re-\nwritten as follows:\nTherefore, Li metal batteries (LMBs) with lithium metal anode (LMA, 3860 mAh g-1)\nhas been reconsidered for future applications39.\n1. Wu, H. et al. Recent progress in understanding solid electrolyte interphase\non lithium metal anodes. Adv. Energy Mater. 11, 2003092 (2021).\n2. Yang, C.-T. & Qi, Y. Maintaining a flat Li surface during the Li stripping\nprocess via interface design. Chem. Mater. 33, 2814-2823 (2021).\n3. Wang, S. et al. 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Breaking the molecular symmetricity of sulfonimide anions for\nhigh-performance lithium metal batteries under extreme cycling conditions. Nat.\nEnergy 10, 191-204 (2025).\n10. Wang, S. et al. A model-based continuous differentiable current charging\napproach for electric vehicles in direct current microgrids. J. Power Sources\n482, 229019 (2021).\n11. Weber, R. et al. Long cycle life and dendrite-free lithium morphology in\nanode-free lithium pouch cells enabled by a dual-salt liquid electrolyte. Nat.\nEnergy 4, 683-689 (2019).\n12. Jie, Y. et al. Towards long-life 500 Wh kg−1 lithium metal pouch cells via\ncompact ion-pair aggregate electrolytes. Nat. Energy 9, 987-998 (2024).\n13. Joshi, T. et al. Safety of lithium-ion cells and batteries at different\nstates-of-charge. J. Electrochem. Soc. 167, 140547 (2020).\n14. Jo, Y. et al. Structural and chemical evolutions of Li/electrolyte interfaces\nin Li-metal batteries: tracing compositional changes of electrolytes under\npractical conditions. Adv. Sci. 10, 2204812 (2023).\n15. Wang, Q. et al. Interface chemistry of an amide electrolyte for highly\nreversible lithium metal batteries. Nat. Commun. 11, 4188 (2020).\n16. Kim, U. S. et al. Modelling the thermal behaviour of a lithium-ion battery\nduring charge. J. Power Sources 196, 5115-5121 (2011).\n17. Seong Kim, U. et al. Modeling the dependence of the discharge behavior of a\nlithium-ion battery on the environmental temperature. J. Electrochem. Soc. 158,\nA611 (2011).\n18. Jäckle, M. et al. Self-diffusion barriers: possible descriptors for dendrite\ngrowth in batteries? Energy Environ. Sci. 11, 3400-3407 (2018).\n19. GarcC-a, G. et al. Exceeding 6500 cycles for LiFePO/Li metal batteries\n4\nthrough understanding pulsed charging protocols. J. Mater. Chem. A 6, 4746-4751\n(2018).\n20. Stein, H. S. C. r. Nonlinear potentiodynamic battery charging protocols for\nfun, education, and application. ACS Eng. Au 4, 345-350 (2024).\n21. Biswal, P. et al. Nucleation and early stage growth of Li electrodeposits.\nNano Lett. 19, 8191-8200 (2019).\n22. Pei, A. et al. Nanoscale nucleation and growth of electrodeposited lithium\nmetal. Nano Lett. 17, 1132-1139 (2017).\n23. Yuan, X. et al. Ultrafast deposition of faceted lithium polyhedra by outpacing\nSEI formation. Nature 620, 86-91 (2023).\n24. Huang, Z. et al. Seeding lithium seeds towards uniform lithium deposition\nfor stable lithium metal anodes. Nano Energy 61, 47-53 (2019).\n25. Mayers, M. Z. et al. Suppression of dendrite formation via pulse charging in\nrechargeable lithium metal batteries. J. Phys. Chem. C 116, 26214-26221 (2012).\n26. Wang, D. et al. Synchronous healing of Li metal anode via asymmetrical\nbidirectional current. iScience, 100781 (2019).\n27. Park, S. H. & Lee, Y. J. Morphological control of electrodeposited lithium\nmetal via seeded growth: stepwise spherical to fibrous lithium growth. J. Mater.\nChem. A 9, 1803-1811 (2021).\n28. Li, L. et al. Self-heating–induced healing of lithium dendrites. Science\n359, 1513-1516 (2018).\n29. Thornton, J. A. High rate thick film growth. Annu. rev. mater. sci. 7, 239-\n260 (1977).\n30. Yoon, G. et al. Deposition and stripping behavior of lithium metal in\nelectrochemical system: continuum mechanics study. Chem. Mater. 30, 6769-6776\n(2018).\n31. Guo, Z. et al. Optimal charging method for lithium ion batteries using a\nuniversal voltage protocol accommodating aging. J. Power Sources 274, 957-964\n(2015).\n32. Yin, Y. et al. New fast charging method of lithium-ion batteries based on a\nreduced order electrochemical model considering side reaction. J. Power Sources\n423, 367-379 (2019).\n33. Aurbach, D. et al. Factors which limit the cycle life of rechargeable lithium\n(metal) batteries. J. Electrochem. Soc. 147, 1274 (2000).\n34. Lu, D. et al. Failure mechanism for fast-charged lithium metal batteries\nwith liquid electrolytes. Adv. Energy Mater. 5, 1400993 (2015).\n35. Shi, F. et al. Lithium metal stripping beneath the solid electrolyte\ninterphase. Proc. Natl. Acad. Sci. 115, 8529 (2018).\n36. Louli, A. J. et al. Optimizing cycling conditions for anode-free lithium\nmetal cells. J. Electrochem. Soc. 168, 020515 (2021).\n37. Shin, J. W. & Chason, E. Compressive stress generation in Sn thin films and\nthe role of grain boundary diffusion. Phys. Rev. Lett. 103, 056102 (2009).\n38. Chason, E. et al. Understanding residual stress in electrodeposited Cu thin\nfilms. J. Electrochem. Soc. 160, D3285 (2013).\n39. Bruce, P. G. et al. Li-O and Li-S batteries with high energy storage. Nat.\n49"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors made substaintial efforts to imporve the manuscripts and all the questions are satisfactorily answered. I recommend for the publication of this manuscript.", "reviewer_2": "The authors have addressed all my prior comments, and I recommend the manuscript for publication in Nature Communications. The results are interesting and noteworthy, the methods are sound and meet the expectations for the journal."}, "author_response": ""}]

Decision letter