Na Metal Anode Research Articles

Conformal Sodium Deposition Facilitated by Ion Adsorption‐Intercalation Process within Hetero‐Interface for Stable Sodium Metal Batteries

AbstractSodium (Na) metal battery is regarded as one of the most promising candidates for large‐scale energy storage devices, benefiting from the abundant sodium reserves and low cost. However, its practical application is hindered by the dendrite growth and unstable electrode‐electrolyte interface. Herein, a 3D sodiophilic structure composed of a carbon matrix overlaid with g‐C3N4 coating layers (g‐C3N4/3D‐C) is designed to stabilize the Na plating/stripping behavior. The sodiophilicity is endowed by a highly reversible adsorption‐intercalation process at the hetero‐interface, which can guide conformal Na deposition and induce the formation of inorganic‐rich solid‐electrolyte interphases with high structural stability and fast Na‐ion transport. Meanwhile, the 3D scaffold can effectively accommodate Na deposition during Na plating/stripping and depress the dendrite formation. As a result, the half cell assembled with g‐C3N4/3D‐C electrode delivers long‐term cycling performance at 1.0 mA cm−2 with a high Coulombic efficiency of 99.92% for over 2000 cycles and of 99.94% even at 5 mA cm−2, 10 mAh cm−2. The practical feasibility of the g‐C3N4/3D‐C is verified with full cells, which shows favorable rate capability and long‐cycle performance. The sodiophilic hetero‐interface construction strategy proposed in this work sparks new insights for designing high‐performance Na metal anodes.

A Multifunctional NaxBi/NaCl Flexible Interface Layer for Solid‐State Na Metal Batteries

AbstractNa3Zr2Si2PO12 (NZSP) electrolyte with excellent air stability and acceptable ionic conductivity demonstrates a significant potential for application in solid‐state Na metal batteries. However, the poor interfacial contact between NZSP and Na anode has severely hindered its practical application. Herein, a BiCl3/polytetrafluoroethylene flexible interface layer is constructed between NZSP and Na metal anode. BiCl3 can react with Na metal to form a multifunctional NaxBi/NaCl‐rich flexible interface layer during the cycling process, which can effectively enhance the interfacial contact, avoid the formation of voids and reduce the interfacial resistance. NaxBi with low energy barrier can provide fast Na+ diffusion path, and NaCl with a wide band gap can inhibit electron injection and suppress Na dendrite growth. Owing to the multifunctional NaxBi/NaCl flexible interface layer, the Na/BiCl3@NZSP/Na symmetric cell exhibits a reduced interfacial resistance from 1252.1 to 67.6 Ω and achieves a high critical current density of 2 mA cm⁻2 at 25 °C. At 0.1 mA cm⁻2/0.1 mAh cm⁻2 and 0.3 mA cm⁻2/0.3 mAh cm⁻2, the symmetric cell can stably cycle for 3000 and 1100 h. Additionally, the Na3V2(PO4)3/BiCl3@NZSP/Na full cell can retain 96.7% of initial capacity (≈111 mAh g−1) after 300 cycles at 0.5 C and excellent rate capability.

Highly Stable Sodium Metal Batteries Enabled by Manipulating the Fluorinated Organic Components of Solid‐Electrolyte‐Interphase

AbstractNa metal batteries (NMBs) stand at the forefront of advancing energy storage technologies, but are severely hampered by Na dendrite issues, especially when using carbonate electrolytes. Suppressing the growth of Na dendrites through constructing NaF‐rich solid‐electrolyte‐interphase (SEI) is a commonly‐used strategy to prolong the lifespan of NMBs. In contrast, fluorinated organic SEI components are often underutilized. Inspired by unveiling the adsorption configuration of fluorinated organic compounds on the surface of Na metal, an optimized SEI architecture for stabilizing NMBs is proposed by investigating the C4H9SO2F‐/C4F9SO2F‐treated Na metal anodes. It is revealed that the SEI built on a fluorinated inorganic/organic hybrid layer exhibit favorable Na passivation capability, significantly improving Na deposition behavior. As a result, the NMB with a high‐loading cathode (15 mg cm−2) and a negative/positive capacity ratio (N/P) ratio of 4 shows a long‐term life span over 1000 cycles with 92.8% capacity retention at 2 C. This work opens a new pathway for developing robust and high‐energy‐density NMBs.

Promoting Cathodic Kinetics and Anodic Stability in Practical Room-Temperature Sodium-Sulfur Batteries with Bifunctional Electrolytes.

The development of room-temperature (RT) sodium-sulfur (Na-S) batteries is severely hindered due to the slow kinetics of the S cathode and the instability of the Na-metal anode. To overcome this, we introduced a dual-functional electrolyte cosolvent, trifluoromethanesulfonamide (TFMSA). Short-chain Na2Sx (1 ≤ x ≤ 2) can be effectively dissolved due to the strong H-S bond interaction between TFMSA and sulfides, which changes the S conversion process, thereby effectively enhancing the conversion kinetics of the cathode. Meanwhile, TFMSA can generate a stable solid electrolyte interphase on the Na-metal surface to protect it from soluble polysulfide attack. Therefore, the RT Na-S batteries using the ether electrolyte show a high initial discharge capacity of 896.6 mAh g-1 and a capacity retention rate of 73% after 150 cycles at 0.2C, and the pouch cell also demonstrates its practical performance. This work proposes a dual-functional electrolyte cosolvent selection principle to inspire the practical application of high-performance RT Na-S batteries.

(Invited) Overcoming Electro-Chemo-Mechanical Limitations of Solid-State Battery Li-Metal and Na-Metal Anodes through 3D Architecture and Tailored Materials/Interfaces

Electro-chemo-mechanical expansion at metal/electrolyte interfaces is a rate limiting factor in solid-state lithium (SSLiBs) and sodium (SSNaBs) batteries. In this presentation we will explain the roles of composition, structure, and interfaces in achieving extremely high current densities for SSNaBs and SSLiBs of 30 mA/cm2 and 100 mA/cm2, respectively, without dendrites at room temperature and no applied pressure.

Liquid Metal Interlayer for Ultrastable Solid-State Sodium Metal Battery.

Solid-state sodium metal batteries have attracted wide attention due to their high energy density, remarkable safety, and abundant sodium resources. However, the growth of Na dendrites and poor interfacial contact between Na metal anode and Na3Zr2Si2PO12 (NZSP) solid-state electrolytes severely limit their practical application. Herein, a wettable liquid metal (GaIn) interlayer significantly reduces the interfacial resistance and avoids the formation of voids at the Na/NZSP interface. Moreover, the Ga4Na and NaIn alloys at the interface caused by the spontaneous reaction of GaIn with Na metal enhance the bond of NZSP with Na anode, which provides a continuous Na+ diffusion pathway and homogeneous Na+ flux to suppress Na dendrite growth. The symmetric cell can cycle stably for over 6500h at 0.05mA cm-2 and over 3000h at 0.1mA cm-2, with a critical current density of 0.8mA cm-2 at 25°C, and the interfacial resistance is significantly reduced to 21.6 Ω from 1095.1 Ω. The full cell coupled with NaNi1/3Fe1/3Mn1/3O2 also shows outstanding cycling performance, maintaining 85.1% capacity after 100 cycles at 0.5 C. This work demonstrates that the liquid metal interlayer has a large potential for the practical application of solid-state metal batteries.

A ZIF-8-enhanced PVDF/PEO blending polymer gel membrane for quasi-solid-state Na-S batteries with long cycling lifespan

Ambient-temperature sodium-sulfur (Na-S) battery with high energy density and low cost has been considered as the promising energy density system. However, its commercial application is limited by the rapid capacity decay of the sulfur electrode and the instability of sodium dendrites with the safety issues. Herein, a ZIF-8 enhanced PVDF/PEO blending polymer gel membrane (PPZ) is reported for stable and safe quasi-solid-state Na-S battery with sulfurized polyacrylonitrile (SPAN) cathode and Na metal anode. The optimized gel polymer membrane with the dense framework exhibited the rapid Na+ migration, superior mechanical property with the tensile strength of 16.5 MPa and the elongation-at-break of 171 %, which is conductive to regulate the Na+ ion flux with the uniform Na plating and prevent the dendritic growth. The assembled symmetric Na/PPZ-GPE/Na cell delivered the stable cycling for 250 h with almost constant voltage hysteresis of 150 mV. Benefited from the superior interfacial stability between PPZ-GPE and Na as well as PPZ-GPE and SPAN, the SPAN/PPZ-GPE/Na cell exhibited the high capacity of 1585.4 mA h g−1 with the capacity retain of 97 % of third cycle after 465 cycles. This work offers exemplary electrolyte design that concurrently and effectively tackles the problems in Na-S battery and presents an excellent quasi-solid sodium-sulfur battery with the high capacity and long cycling.

Synergetic Dual-Additive Electrolyte Enables Highly Stable Performance in Sodium Metal Batteries.

Sodium (Na)-metal batteries (SMBs) are considered one of the most promising candidates for the large-scale energy storage market owing to their high theoretical capacity (1,166 mAh g-1) and the abundance of Na raw material. However, the limited stability of electrolytes still hindered the application of SMBs. Herein, sulfolane (Sul) and vinylene carbonate (VC) are identified as effective dual additives that can largely stabilize propylene carbonate (PC)-based electrolytes, prevent dendrite growth, and extend the cycle life of SMBs. The cycling stability of the Na/NaNi0.68Mn0.22Co0.1O2 (NaNMC) cell with this dual-additive electrolyte is remarkably enhanced, with a capacity retention of 94% and a Coulombic efficiency (CE) of 99.9% over 600 cycles at a 5 C (750mA g-1) rate. The superior cycling performance of the cells can be attributed to the homogenous, dense, and thin hybrid solid electrolyte interphase consisting of F- and S-containing species on the surface of both the Na metal anode and the NaNMC cathode by adding dual additives. Such unique interphases can effectively facilitate Na-ion transport kinetics and avoid electrolyte depletion during repeated cycling at a very high rate of 5 C. This electrolyte design is believed to result in further improvements in the performance of SMBs.

Stable room-temperature sodium-sulfur battery enabled by pre-sodium activated carbon cloth anode and nonflammable localized high-concentration electrolyte

Room-temperature (RT) sodium-sulfur (Na–S) battery is a promising energy storage technology with low-cost, high-energy-density and environmental-friendliness. However, the current RT Na–S battery suffers from various problems, such as poor cycling stability and poor electrolyte-electrode compatibility caused by polysulfide shuttling and active Na-metal anode. Here, a nonflammable localized high-concentration electrolyte (LHCE) (sodium bis(trifluoromethanesulfonyl)imide salt, sulfolane solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether diluent in a molar ratio of 1:2:2), and a pre-sodium activated carbon cloth (NaACC) anode, are combined to enable stable and high-safety RT Na–S battery. In LHCE, the shuttle effect of polysulfide is greatly alleviated, a stable anions-derived NaF-rich cathode electrolyte interphase is formed, and a solid-solid conversion mechanism of a solid S8-solid Na2Sn (1 ≤ n ≤ 3) is achieved. Meanwhile, the Na dendrites and side reactions between electrolyte and anode are effectively inhibited by using NaACC anode. Therefore, under the synergistic effect of electrolyte regulation and negative electrode structure optimization, although using a low N/P ratio of 1.7, the RT Na–S battery also delivers a high initial capacity of 1220.8 mAh g−1, good rate capability and stable cycling performance with a high average Coulombic efficiency of 99.1 %. The capacity still remains at 704.5 mAh g−1 after 100 cycles. This innovative combination of LHCE and NaACC anode in Na–S batteries provides a new idea for further achieving stable RT Na–S batteries with long-cycle-life and high-safety.

A Critical Review on Room-Temperature Sodium-Sulfur Batteries: From Research Advances to Practical Perspectives.

Room-temperature sodium-sulfur (RT-Na/S) batteries are promising alternatives for next-generation energy storage systems with high energy density and high power density. However, some notorious issues are hampering the practical application of RT-Na/S batteries. Besides, the working mechanism of RT-Na/S batteries under practical conditions such as high sulfur loading, lean electrolyte, and low capacity ratio between the negative and positive electrode (N/P ratio), is of essential importance for practical applications, yet the significance of these parameters has long been disregarded. Herein, it is comprehensively reviewed recent advances on Na metal anode, S cathode, electrolyte, and separator engineering for RT-Na/S batteries. The discrepancies between laboratory research and practical conditions are elaborately discussed, endeavors toward practical applications are highlighted, and suggestions for the practical values of the crucial parameters are rationally proposed. Furthermore, an empirical equation to estimate the actual energy density of RT-Na/S pouch cells under practical conditions is rationally proposed for the first time, making it possible to evaluate the gravimetric energy density of the cells under practical conditions. This review aims to reemphasize the vital importance of the crucial parameters for RT-Na/S batteries to bridge the gaps between laboratory research and practical applications.

Durable sodium iodide interphase stabilizing sodium metal anodes

The implementation of sodium metal batteries (SMBs) is known for their low cost and high energy density. However, a major concern in SMBs is the formation of dendrites on the Na metal anode, which can potentially cause short circuits and compromise safety. Herein, to address this issue, we propose a novel approach to create a protective layer by decorating Na surface with NaI particles. This protective layer exhibits a high Young’s modulus and excellent sodium ion transference ability. As a result, the lifespan of the Na/NaI||Na/NaI cell is significantly extended to 850 h at 0.5 mA cm−2/1 mAh cm−2. Furthermore, when the Na/NaI anode is combined with a Na3V2(PO4)3 (NVP) cathode, the full cell retains 83 mAh g−1 (approximately 94% of its initial capacity) even after 1500 cycles at 5 C. Overall, this work presents a simple and effective method for establishing a protective layer on the Na surface, thereby enabling the realization of long lifespan and stable SMBs.

Cobalt nanoparticles embedded in nitrogen-doped carbon nanofibers to enhance redox kinetics for long-cycling sodium–sulfur batteries

The shuttle effect resulting from severe volume expansion and polysulfide dissolution imposes limitations to the application of sodium–sulfur (Na–S) batteries. Herein, a three-dimensional self-supported electrode comprised of cobalt nanoparticles embedded in nitrogen-doped carbon nanofibers (CoNCNFs) is constructed to accommodate sulfur as the cathode for Na–S batteries. The carbon fiber framework facilitates direct electrons transmission and reduces the overall contact impedance of the electrode. The abundant pore structure not only promotes electrolyte infiltration but also ensures high loading of sulfur and provides space for volume expansion during charging and discharging. Most significantly, the CoNCNF carrier accelerates the conversion rate of sodium polysulfides into Na2S and guide Na2S deposition on its surface in a three-dimensional progressive nucleation (3DP) mode, resulting in a high Na2S deposition capacity and outstanding long-term cycling performance. When coupled with a Na-metal anode, the CoNCNF/S composite cathode exhibits stable electrochemical properties with a capacity up to 1030.2 mA h/g after 300 cycles at 0.2 C and excellent rate performance.

An Ultrastable Low-Temperature Na Metal Battery Enabled by Synergy between Weakly Solvating Solvents.

The low ionic conductivity and high desolvation barrier are the main challenges for organic electrolytes in rechargeable metal batteries, especially at low temperatures. The general strategy is to couple strong-solvation and weak-solvation solvents to give balanced physicochemical properties. However, the two challenges described above cannot be overcome at the same time. Herein, we combine two different kinds of weakly solvating solvents with a very low desolvation energy. Interestingly, the synergy between the weak-solvation solvents can break the locally ordered structure at a low temperature to enable higher ionic conductivity compared to those with individual solvents. Thus, facile desolvation and high ionic conductivity are achieved simultaneously, significantly improving the reversibility of electrode reactions at low temperatures. The Na metal anode can be stably cycled at 2 mA cm-2 at -40 °C for 1000 h. The Na||Na3V2(PO4)3 cell shows the reversible capacity of 64 mAh g-1 at 0.3 C after 300 cycles at -40 °C, and the capacity retention is 86%. This strategy is applicable to other sets of weak-solvation solvents, providing guidance for the development of electrolytes for low-temperature rechargeable metal batteries.

Ultra-stable dendrite-free Na and Li metal anodes enabled by tin selenide host material

Lithium/sodium metal anodes are considered promising candidates to realize high-energy–density batteries because of their high theoretical specific capacity and low potential. However, their cycling stability are hindered by uncontrolled dendrites growth. Herein, SnSe nanoparticles are tightly anchored on the fiber of carbon cloth (CC) to construct SnSe@CC host material in order to control Li/Na nucleation behavior and restrain dendrites growth. It is demonstrated that the alloying product of Li15Sn4/Na15Sn4 with strong metal affinity can provide abundant active nucleation sites, and three-dimensional structure of CC host can significantly decrease the local electric current, thereby guiding homogeneous metal deposition without Li and Na dendrites. Meanwhile, the conversion product of Li2Se/Na2Se will uniformly cover on the surface of metal to serve as ultra-stable solid state interface film. As a result, high-capacity Li metal anode (20 mAh·cm−2) and Na metal anode (10 mAh·cm−2) can work steadily with ultra-long lifespans over 5000 and 6000 h with low overpotentials of 7 mV and 141 mV, respectively. Moreover, the assembled Li and Na metal full batteries exhibit superior electrochemical performances, confirming the practicability of metal anode confined in composite host. Such a strategy of conversion-alloying-type materials as hosts opens up a new path for dendrite-free metal anode electrode.

Constructing sodiophilic interconnected ion-transport channels towards a stable Na-metal anode

Tuning the electrochemical behaviors of Na metal anodes via building Na+-conducting channels through a facile rolling and folding method.

A Glass-Interphase for Highly Reversible and Stable RT-Na/S Batteries

Owing to the high theoretical specific capacity (1165 mA h g-1), high natural abundance, and low redox potential (-2.71 V vs standard hydrogen electrode), sodium metal is considered as an ideal anode material for the next-generation high-energy batteries. Though, a high-temperature variant of the sodium-sulfur batteries has already been commercialized, its compromised safety (due to high-temperature operation, 250 – 300 ⁰C) has triggered the research interest in developing its room-temperature analogue. At room-temperature, the thermodynamic instability of Na metal with the liquid electrolytes often leads to develop a thick and chemically unstable interphase, often called the solid electrolyte interphase (SEI). Upon Na plating/stripping, the SEI grows and dissolves repeatedly, results in consuming both the Na anode and the electrolyte inventory. The Na dendrites, the primary unknown risk associated with Na metal-based batteries, are inclined to develop from the fractured sites of the SEI. The SEI exfoliation can be attributed to weak chemical adhesion between the SEI and the Na metal anode. Functional additives, engineered solvents, and the high concentration electrolytes have often been used to alter the mechanical and electrochemical properties of the SEI. It is apparent that, a stable and durable SEI is the key to creating a secure, dendrite-free, and long-lasting RT-Na/S batteries.More recently, the idea of glass-electrolytes to stabilize the metal anodes is disclosed by the Nobel laureate Prof. J. Goodenough. The glass-electrolyte is used to suppress the dendrite growth and ensured improved safety of the high-energy metal-sulfur batteries. However, the cell experiences a huge interfacial resistance due to metal anode/glass-electrolyte interface.The present work relates to the development of a glass-interphase for RT-Na/S batteries. The interphase is grown directly over the sodium metal anode through a simple and scalable approach. To growth the interphase, a novel organic molecule is used to facilitate the formation of the glass-interphase, and called as “glass-interphase forming additive (GIFA). In general, GIFAs contains the hydrolysable group, which is commonly an amine, acyloxy, alkoxy, or halogen on one side, and one Si atom. It contains organo-functional group, such as epoxide, on other side. The presence of oxide or hydroxide is essential in realizing interaction of GIFA with the sodium metal surface.

Electrochemical Strategies to Control Dendritic Growth in Sodium-Metal Batteries

Sustainable development can be pursued through electrification in all sectors, and energy storage devices -mainly batteries- play a crucial role in this process. This leads to an ever-increasing demand for rechargeable batteries. However, the current generation of the rechargeable batteries, namely lithium-ion batteries, is produced using elements such as Li, Ni, and Co which have limited resources. Sodium-ion batteries (SIBs) on the other hand are considered as a good alternative due to the abundance of Na resources and fundamental similarities of Na and Li. While the cathode material for SIBs has reached a commercial level of reliability, the identification of a high energy anode material still remains a challenge. Although Na metal as an anode material offers high energy density, the main issue is that Na metal has a tendency for dendritic growth during electrodeposition.In this work, different electrochemical strategies are used to mitigate dendritic Na growth. High overpotential nucleation pulses during stripping and/or plating steps are applied in order to induce two-dimensional growth. The impact of these strategies is studied using three-electrode symmetrical cells with Na metal as the working, counter, and reference electrodes, in an electrolyte composed of NaPF6 in EC/PC with FEC as an additive. Chronopotentiograms recorded during extended cycling (with and without Na pre-nucleation) are examined with special attention being paid to the overpotentials occurring on each cycle. Ex-situ SEM images are used to relate the different potential profiles during extended galvanostatic cycling to the different surface morphologies.The results show that a combination of oxidative (stripping) and reductive (plating) pulses has an obvious effect on inhibiting dendritic growth during electrodeposition of Na metal. The results encourage the deployment of electrochemical strategies to prevent dendritic growth in Na metal anodes and paves the way for experiments with new electrolyte compositions to further help overcoming the challenges associated with Na deposition.

Highly Fluorinated and Boron Containing Anion Derived Stable Anode and Cathode Interfaces for Long Cycle and High Voltage Sodium Metal Batteries

Sodium metal is a propitious anode for the development of next generation metal batteries owing to its low reduction potential (-2.71 V) and high theoretical capacity (1165 mAh g-1)1. Among various electrolytes, carbonate solvents can be useful to develop high voltage metal batteries with wide temperature range2. However, the aggressive reactivity of sodium metal in carbonate electrolytes lead to the formation of unstable solid electrolyte interface on the metal anode which renders poor long cycling performance to the battery3. In this work, we have fabricated thin and inorganic components (F and B rich) rich solid electrolyte interface (SEI) on Na metal anode and cathode electrolyte interface (CEI) on oxide-based cathode to improve long cycling stability of sodium metal battery. Here, fluorine (F) and boron (B) containing anion is compared with conventional hexafluorophosphate anion (PF6-) in binary carbonate solvent system (EC:EMC). The stable stripping/plating behaviour of both symmetric (Na/Na) and asymmetric cell (Al/Na) in case of F and B containing anion is found compared to the PF6 - anion.The excellent long-term cycling stability of full cell (Na/Na0.67Fe0.5Mn0.5O2) is further attributed to the improved electrochemical stability window and better aluminium passivation on employing F and B containing anion in the electrolyte system as compared to PF6 - anion. The dual role of F and B containing anion to form stable interfaces on both the anode and cathode side provides a pathway in the development of fluorinated electrolytes for high voltage sodium metal batteries.

Review of Separator Modification Strategies: Targeting Undesired Anion Transport in Room Temperature Sodium–Sulfur/Selenium/Iodine Batteries

AbstractRechargeable sodium–sulfur/selenium/iodine (Na–S/Se/I2) batteries are regarded as promising candidates for large‐scale energy storage systems, with the advantages of high energy density, low cost, and environmental friendliness. However, the electrochemical performances of Na–S/Se/I2 batteries are still restricted by several inherent issues, including the “shuttle effect” of polysulfides/polyselenides/polyiodides (PSs/PSes/PIs), sluggish kinetics of the conversion reactions at the cathodes, and Na dendrite growth at the anodes. Among these challenges, uncontrolled “shuttle effect” of PSs/PSes/PIs is a major contributing factor for the irreversible loss of active cathode materials and severe side reactions on Na metal anodes, leading to rapid failure of the batteries. Separator modification has been demonstrated to be an effective strategy to suppress the shuttling of PSs/PSes/PIs. Herein, the latest achievement in modifying separators for high‐performance Na–S/Se/I2 batteries is comprehensively reviewed. The reaction mechanisms of each battery system are first discussed. Then, strategies of separator modification based on the different functions for regulating the transportation of PSs/PSes/PIs are summarized, including applying electrostatic repulsive interaction, introducing conductive layers, improving sieving effects, enhancing chemisorption capability, and adding efficient electrocatalysts. Finally, future perspectives on the practical application of modified separators in high‐energy rechargeable batteries are provided.

Influence of Interfacial Voids and Grain Boundary Conductivity on Depletion Kinetics of Sodium Metal Anodes in All-Solid-State Batteries

An electrochemical micro-scale phase-field model is developed to simulate the stripping and plating kinetics of a Na-metal anode in all-solid-state Na-ion batteries. In this model, in addition to the metallic anode and ceramic separator regions, a highly conductive but Na-poor region representing the free space is assumed to simulate the shrinking of the Na-anode during electro-stripping and its growth during plating. For a perfect anode/separator interface, we find that the growth and depletion kinetics are linear. However, the presence of multiple interfacial voids at the anode/separator interface causes deviation from this linear behaviour. Finally, we show that depletion kinetics is also proportional to the ratio of the grain boundary conductivity to that of the grain conductivity (σgb/σg) in the separator phase, either with or without interfacial voids.