David Mitlin

NASICON Sodium Metal All Solid-State Electrolyte An electric float plane landed on a remote lake in Katmai National Park and is being fueled for the return trip using a standalone solar-powered charging station. The solid-state sodium batteries inside the plane are based on an advanced NASICON-type electrolyte, which is both durable and low cost. The environmentalist who traveled to this location to live among the bears is proud of his low CO2 footprint, which may soon go to net zero. More details can be found in the Research Article by Callum J. Campbell, David Mitlin, and co-workers (DOI: 10.1002/adma.202512961).

Thin Lithium Metal Battery Anode Fabrication In their Review (DOI: 10.1002/adma.202511817), Wei Liu, David Mitlin and his co-workers discuss the fundamental science underlying the processing of thin lithium-metal anodes. They examine emerging strategies aimed at enabling the lithium-thinning process and the associated structural evolutions. Critical challenges and future prospects are proposed to guide innovative roll-to-roll battery manufacturing, drawing parallels to the classic printing industry.

Fluoroethylene carbonate (FEC) has garnered widespread recognition for its beneficial role in improving the electrochemical performance of lithium (Li)-metal batteries; however, its role in alleviating interface instability of sodium (Na)-metal electrodes remains poorly understood. In this work, we show that, instead of stabilizing the Na electrode, in a conventional porous glass fiber separator-based cell, FEC induces spatial and chemical heterogeneities in the solid electrolyte interphase (SEI), resulting in nonuniform morphological growth at the anode interface. These heterogeneities lead to severe morphological instability and interfacial degradation, with stable cycling limited to less than 30 h, even at low current densities, highlighting the unresolved challenges of FEC utilization in standard separator conditions. Mesoscale modeling further describes how spatial heterogeneity of the SEI, compounded by localized chemical variations due to FEC, promotes nonuniform Na deposition and drives localized hotspots for nucleation and growth. To further interrogate the role of heterogeneity, we show that incorporating well-controlled anodized aluminum oxide separators facilitates uniform SEI formation. This approach mitigates the transport heterogeneity, leading to a more uniform plating/stripping morphology, and maintains a continuous operation for over 600 h with minimal overpotential fluctuation. This study reveals that long-term Na-metal stability in a carbonate electrolyte is governed not only by additive chemistry but also critically by the spatial and chemical homogeneity of the interface enabled through separator architecture.

ABSTRACT The rapid growth of lithium‐ion batteries (LIBs) applications drives the need for fast‐charging solutions ensuring speed, safety, durability, and performance. Such charging protocol design needs to be guided by mechanistic understanding of degradation pathways, ionic transport limitations, and thermal constraints. However, in practice, many charging protocols used in commercial electronics and electric vehicles (EVs) have limited mechanistic transparency. In this review, we adopt a reverse perspective by extracting mechanistic insights from practical charging protocols to inform future design. To this end, standardized fast‐charging protocols and those implemented in real‐world applications such as smartphones and EVs are analyzed to examine how their voltage–current profiles evolve with state‐of‐charge (SOC) and to reflect distinct design rationales. These features are further examined in terms of SOC‐dependent physical and chemical transformations in electrode materials, kinetic limitations such as polarization and reaction heterogeneity influenced by charging protocol design, and distinct heat generation patterns governed by protocol characteristics. Advanced characterization techniques are then highlighted for providing real‐time insights into structural transitions, diffusion kinetics, and heat evolution during fast charging. Finally, future protocol design may be informed by multiscale material modelling, real‐time sensing for adaptive control, and data‐driven optimization to support the development of advanced fast‐charging systems.

Electrochemical stability of anode-free all solid-state battery (AF-ASSB) based on argyrodite Li 6 PS 5 Cl (LPSCl) requires control of two distinct solid electrolyte interphases, SEI-1 and SEI-2. With an "empty" current collector used in AF-ASSB there are three active interfaces; lithium metal - SE interphase (SEI-1), lithium - current collector interface, and collector - SE interphase (SEI-2) where copper sulfides are formed even without external current. Bilayer of 140nm magnesium / 30nm tungsten (Mg/W-Cu) controls these and allows for state-of-the-art electrochemical performance in half-cells and full cells. AF-ASSB with NMC811 cathode achieves 150 cycles with Coulombic efficiency (CE) above 99.8%. With high mass-loading cathode (8.6 mAh cm -2 ), AF-ASSB retains 86.5% capacity after 45 cycles at 0.2C. During electrodeposition of Li, gradient Li-Mg solid solution is formed, which reverses upon electrodissolution. This promotes conformal wetting/dewetting by Li and stabilizes SEI-1 by lowering thermodynamic driving force for SE reduction. Inert refractory W underlayer is required to prevent ongoing formation of SEI-2, which also drives electrochemical degradation. Inert Mo and Nb layers likewise protect Cu, while Li-active layers (Mg, Sn) do not due to pulverization. Mechanistic explanation for observed Li segregation within alloying Li x Mg layer is provided through mesoscale modelling, considering diffusivity and stress. Front Cover: Control of Two Solid Electrolyte Interphases at the Negative Electrode of an Anode ‐ Free All Solid ‐ State Battery based on Argyrodite Electrolyte. Advanced Materials. 2025 Jan 6:2410948.

Sodium ion batteries (SIBs) and sodium metal batteries (SMBs) are promising options in next-generation energy storage technology. For anode-free SMBs (AF-SMBs), where the cathode is the only ion reservoir, the challenge is to achieve stable electrodeposition/dissolution onto an "empty" current collector, rather than onto pre-existing sodium metal. Despite recent advances, the heterogeneous nature of the reactive growing/shrinking metal - electrolyte interphase remains not fully understood. This study examines how current collector support chemistry (sodiophilic intermetallic Na 2 Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm -2 , 0.5-3 mA cm -2 ) representative of commercially relevant mass loading in anode-free sodium metal battery (AF-SMBs) are analyzed. Synchrotron X-ray nanotomography and grazing-incidence wide-angle X-ray scattering (GIWAXS) are combined with cryogenic focused ion beam (cryo-FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te-Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modelling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability. Front Cover: Lo CA, Wang Y, Kankanallu VR, Singla A, Yen D, Zheng X, Naik KG, Vishnugopi BS, Campbell C, Raj V, Zhao C. Interdependence of Support Wettability‐Electrodeposition Rate‐Sodium Metal Anode and SEI Microstructure. Angewandte Chemie. 2024 Nov 12:e202412550.

Anode-free all-solid-state batteries (AF-ASSBs) offer a promising pathway toward high-energy-density storage by eliminating excess lithium, relying instead on lithium sourced from the cathode. [1-2] This architecture has the potential to achieve over 50% higher volumetric energy density than conventional Li metal. Among various solid-state electrolytes (SSEs), argyrodite-type Li 6 PS 5 Cl (LPSCl) stands out due to its high ionic conductivity (>10 -3 S cm -1 at room temperature) and mechanical compliance, which enhances interfacial contact with both electrodes. However, long-term electrochemical stability remains a critical challenge, particularly at the interfaces. In this presentation, I will explore the design principles for current collectors that promote stable cycling in AF-ASSBs employing LPSCl SSE. Key factors such as metal wetting behavior, interfacial stability between the electrolyte and both the current collector and electrodeposited lithium will be discussed. Advanced characterization techniques, including cryogenic electron microscopy (Cryo-EM) and multiscale modeling, provide valuable insights into the composition and evolution of these interfaces. By leveraging these findings, I will highlight strategies to mitigate degradation and enhance AF-ASSB performance, paving the way for practical implementation. [1] Y. Wang, Y. Liu, M. Nguyen, J. Cho, N. Katyal, B. S. Vishnugopi, H. Hao, R. Fang, N. Wu, P. Liu, P. P. Mukherjee, J. Nanda, G. Henkelman, J. Watt, D. Mitlin, Adv. Mater. 2023 , 35, e2206762. [2] Y. Wang, V. Raj, K. G. Naik, B. S. Vishnugopi, J. Cho, M. Nguyen, E. A. Recker, Y. Su, H. Celio, A. Dolocan, Z. A. Page, J. Watt, G. Henkelman, Q. H. Tu, P. P. Mukherjee, D. Mitlin, Adv. Mater. 2025 , 37, e2410948.

Microstructure of argyrodite solid-state electrolyte (SSE) critically affects lithium metal electrodeposition/dissolution. While the stability of unmodified SSE is mediocre, once optimized state-of-the-art electrochemical performance is achieved (symmetric cells, full cells with NMC811) without secondary interlayers or functionalized current collectors. Planetary mechanical milling in wet media (m-xylene) is employed to alter commercial Li 6 PS 5 Cl (LPSCl) powder. Quantitative stereology demonstrates how milling progressively refines grain and pore size/distribution in the SSE compact, increases its density, and geometrically smoothens the SSE-Li interface. Mechanical indentation demonstrates that these changes lead to reduced site-to-site variation in the compact's hardness. Milled microstructures promote uniform early-stage electrodeposition on foil collectors and stabilize solid electrolyte interphase (SEI) reactivity. Analysis of half-cells with bilayer electrolytes demonstrates the importance of microstructure directly contacting current collector, with interface roughness due to pore and grain size distribution being key. For the first time, short-circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter "mini" symmetrical cell and cryogenic focused ion beam (cryo-FIB) electron microscopy. The branching sheet-like dendrite traverses intergranularly, filling the interparticle voids and forming an SEI around it. Mesoscale modeling reveals the relationship between Li-SSE interface morphology and the onset of electrochemical instability, based on underlying reaction current distribution. Wang Y, Hao H, Naik KG, Vishnugopi BS, Fincher CD, Yan Q, Raj V, Celio H, Yang G, Fang H, Chiang YM. Mechanical Milling–Induced Microstructure Changes in Argyrodite LPSCl Solid‐State Electrolyte Critically Affect Electrochemical Stability. Advanced Energy Materials . 2024 Apr 13:2304530.

Abstract Reactive carbide precursor‐based synthesis of NASICON‐type NZSP (Na 1+x Zr 2 Si x P 3‐x O 12 ) solid‐state electrolyte (SSE) is demonstrated, in contrast to the established oxide‐based approach. Exothermic decomposition of ZrC and SiC in air homogenizes microstructure, yielding 98% compact density after conventional sintering at 1200 °C. Quantitative stereology demonstrates that significant microstructural differences are present. Compacts of carbide‐derived Carb‐NZSP are 98% dense with a secondary zirconium oxide (ZrO 2 ) volume fraction of 0.2% ± 0.3%, versus 93% dense and 3% ± 1% for oxide‐derived baseline. For Carb‐NZSP, the secondary glassy phosphate phase is agglomerated, while for baseline, it is dispersed and percolated. Electrochemical testing combined with post‐mortem analysis demonstrates how microstructural control of secondary phases is critical for dendrite suppression: Carb‐NZSP critical current density (CCD) is 3.1 ± 0.8 mA cm − 2 at 0.1 mAh cm − 2 , versus 1.0 ± 0.7 mA cm −2 at 0.1 mAh cm −2 . Cryogenic focused ion beam (cryo‐FIB) analysis demonstrates that in both materials, the porous 2D sheet‐like sodium metal dendrites propagate around and subsume NZSP grains, likely following a path enriched with glassy phase and with porosity. Dendrites also flow around isolated zirconia particles. Phase field simulation reveals deflection of dendrites by mechanically tough zirconia, while brittle glassy phase accelerates dendrite growth, especially when finely distributed.

While lithium metal foils used for research may be upward of 250 µm in thickness, anodes for viable lithium metal batteries (LMBs) must be at least one order of magnitude thinner. This review focuses on fabrication approaches that promise to bridge this divide, highlighting the known/unknown processing - microstructure - electrochemical properties interrelations. Four general methodologies are discussed, starting with metallurgical ingot extrusion and rolling, followed by solidification casting, solution-based wet methods, and physical vapor deposition (PVD). Each section begins with an outline of the underlying principles of the approach and how this limits the minimal thickness, morphology, bulk microstructure, and surface chemistry of the resultant anodes. The discussion then moves to specific case studies that illustrate how various state-of-the-art research efforts have overcome these limitations by employing a range of strategies that include alloy and composite metallurgies, functionalized current collector coatings, and liquid-phase additives. It is highlighted that methodologies resulting in planar and conformal lithium films, and subsequently improving electrochemical performance, are fairly consistent across all four fabrication classes. Each section concludes with a critical discussion of the research necessary to advance the field, identifying key outstanding scientific questions and "unknowns."

Sonar-based identification of underwater unexploded ordinance (UXO) is a potentially powerful technique for aiding in clean-up of former military sites, in which recovery of munitions is essential for public safety. We hypothesize that as UXO age for long periods of time in the underwater environment, accumulated effects of corrosion and material loss lead to increasingly larger deviation of the acoustic scattering signature from the pristine state, thus potentially confounding sonar-based target classification algorithm performance. To investigate this, a set of World-War-II-era miniature practice bombs (model AN-Mk 23), recovered from a brackish pond after about 80 years exposure, were obtained. Free-field acoustic color measurements were conducted on the samples, which exhibited a range of corrosion-erosion damage, in addition to clean, uncorroded samples and clutter objects for comparison. Analysis was conducted to isolate various corrosion effects on the acoustic signature. Additionally, we investigated impacts of corrosion on the performance of select classification algorithms. [Work sponsored by SERDP and DOD SMART Scholarship.]

Abstract The micromorphology of composite cathodes is known to play a vital role in determining all‐solid‐state battery (ASSB) performance. However, much of our current understanding is derived from empirical observations, lacking a deeper mechanistic foundation. The “rocking chair” concept of battery chemistry requires maintaining charge neutrality, emphasizing the necessity of examining electrode micromorphology from the perspective of conductive networks. This study systematically investigates the microscopic electrochemical impacts of conductive network micromorphology by varying the Li + ‐to‐e − channel ratio in cathodes comprising LiNbO 3 ‐coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 , Li 6 PS 5 Cl, and carbon fibers. Utilizing multiscale synchrotron‐based spectro‐microscopy, we unravel that unbalanced Li + and e − conducting channels intensify charge polarization within active cathode particles and accelerate their degradation. A further model system with X‐ray nano‐tomography resolved e − and Li + channels indicates that spatially uniform and well‐paired Li + and e − conducting channels are highly desirable as they could promote more uniform lithiation/delithiation, mitigating microscopic electrochemical polarization. Electrode‐scale X‐ray holotomography analysis reveals that the impact of conductive networks is particle‐size‐dependent, with smaller cathode particles being more significantly affected. These findings provide mechanistic insights into the interplay between conductive networks and all‐solid‐state battery operation, laying the groundwork for rational design and optimization of cathode architectures in future solid‐state battery technologies.

Abstract The micromorphology of composite cathodes is known to play a vital role in determining all‐solid‐state battery (ASSB) performance. However, much of our current understanding is derived from empirical observations, lacking a deeper mechanistic foundation. The “rocking chair” concept of battery chemistry requires maintaining charge neutrality, emphasizing the necessity of examining electrode micromorphology from the perspective of conductive networks. This study systematically investigates the microscopic electrochemical impacts of conductive network micromorphology by varying the Li + ‐to‐e − channel ratio in cathodes comprising LiNbO 3 ‐coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 , Li 6 PS 5 Cl, and carbon fibers. Utilizing multiscale synchrotron‐based spectro‐microscopy, we unravel that unbalanced Li + and e − conducting channels intensify charge polarization within active cathode particles and accelerate their degradation. A further model system with X‐ray nano‐tomography resolved e − and Li + channels indicates that spatially uniform and well‐paired Li + and e − conducting channels are highly desirable as they could promote more uniform lithiation/delithiation, mitigating microscopic electrochemical polarization. Electrode‐scale X‐ray holotomography analysis reveals that the impact of conductive networks is particle‐size‐dependent, with smaller cathode particles being more significantly affected. These findings provide mechanistic insights into the interplay between conductive networks and all‐solid‐state battery operation, laying the groundwork for rational design and optimization of cathode architectures in future solid‐state battery technologies.

Abstract This work elucidates the mechanism by which lithium borohydride (LiBH 4 ) doping into argyrodite‐type Li 6 PS 5 Cl (LBH‐LPSCl) solid‐state electrolyte (SSE) enhances electrochemical stability. State‐of‐the‐art electrochemical performance is achieved with 5 wt% borohydride. Symmetric cells achieve critical current density (CCD) of 7.3 mA cm −2 , versus 2.6 mA cm −2 for baseline‐LPSCl. All solid‐state batteries (ASSBs) employing lithium metal and NMC811 cathode are stable over 400 cycles at 0.5C, with capacity retention of 83%. An anode‐free ASSB (AF‐ASSB) is stable over 600 cycles, with capacity loss of 0.04% per cycle. 5LBH‐LPSCl allows for enhanced low temperature operation, down to −14 °C. Yet the difference in electrolytes’ bulk microstructures and hardnesses are minimal, while ionic conductivity is incrementally improved (≈50%). Theoretical modeling indicates limited effect of substitution on thermodynamic stability of PS 4 3− units, which decompose when contacting Li. Instead, enhanced electrochemical stability is site‐specific kinetic effect: In situ electrodeposition experiments using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) reveal tri‐layer SEI based predominately on Li 3 P/LiBH 4 /Li 2 S that blocks electrons while facilitating ion transport. This SEI manifests reduced interface resistance and accelerated nucleation and growth of metallic Li. With baseline‐LPSCl the SEI based on Li 3 P/Li 2 S is substantially thicker, generating localized stresses that promote interfacial cracking while cycling.

Sodium (Na) anodes hold significant potential to meet the growing demand for high-energy-density electrochemical energy storage and an alternative to lithium metals. Achieving long-lasting stability at the metal-electrolyte interface is crucial for the development of emerging sodium metal-based electrochemical energy storage technologies. Currently, fundamental knowledges about the deposition and stripping processes of Na metal anodes remain lacking. These processes typically involve uncontrolled dendritic growth and the formation of a solid electrolyte interphase (SEI) that does not effectively protect the metal from the electrolyte. To better understand the relationship between Na deposits and SEI, we employed advanced synchrotron X-ray characterization techniques, including X-ray nanotomography, grazing-incidence wide-angle X-ray scattering (GIWAXS), and soft X-ray spectroscopy (sXAS). These techniques are complementary: X-ray nanotomography reveals morphological changes, GIWAXS provides insights into crystal structures, and sXAS offers detailed chemical information. Together, they enable a comprehensive understanding of the underlying mechanisms. Additionally, operando GIWAXS was used to monitor the evolution of Na deposits and their SEI in real time. Our results indicate that the wettability of current collectors (Te-Cu: sodiophilic vs. Cu: sodiophobic) significantly influences both the crystallographic orientation of Na deposits, affecting film morphology and internal porosity, and the distribution of SEI components. Specifically, sodium fluoride (NaF) is more prevalent in the SEI formed on Te−Cu collectors, while sodium hydride (NaH) and sodium hydroxide (NaOH) dominate on baseline Cu collectors[1]. Overall, this multimodal approach provides valuable insights into the mechanisms of Na deposition and dissolution, offering a pathway to control the reaction and realize practical applications. Reference: [1] Lo, Chang-An, et al. "Interdependence of Support Wettability‐Electrodeposition Rate‐Sodium Metal Anode and SEI Microstructure." Angewandte Chemie (2024): e202412550.

Abstract We employed accumulative roll bonding to fabricate self‐standing metallurgical composite of in situ formed alkaline potassium‐bismuth‐telluride intermetallic K 2 (Bi 2/6 Te 3/6 Vac 1/6 ) embedded in potassium metal. This newly discovered thermodynamically stable potassiophilic crystal, termed “KBT”, is fcc antifluorite with K 2 Te archetype. Symmetric cells achieve 880 h of cycling at 0.5 mA cm −2 and 0.5 mAh cm −2 . Potassium metal battery (KMB) with Prussian blue (PB) cathode in carbonate electrolyte retains 80% capacity after 200 cycles at 1C. In ether‐based electrolyte with organic cathode, it achieves 80% retention after 900 cycles at 2C. Combined synchrotron X‐ray nano‐tomography, cryogenic‐focused ion beam microscopy (Cryo‐FIB) and sputter‐down X‐ray photoelectron spectroscopy (XPS) demonstrate uniform electrodeposits, versus baseline of potassium filaments intermixed with pores and coarse SEI. Binary K 3 Bi‐K and K 2 Te‐K intermetallic supports also provide improved electrochemical performance, albeit to lesser extent. Multiscale simulation provides insight into role of support structure in adatom energetics, film nucleation, early‐stage SEI morphology and interfacial stability.

Abstract We employed accumulative roll bonding to fabricate self‐standing metallurgical composite of in situ formed alkaline potassium‐bismuth‐telluride intermetallic K 2 (Bi 2/6 Te 3/6 Vac 1/6 ) embedded in potassium metal. This newly discovered thermodynamically stable potassiophilic crystal, termed “KBT”, is fcc antifluorite with K 2 Te archetype. Symmetric cells achieve 880 h of cycling at 0.5 mA cm −2 and 0.5 mAh cm −2 . Potassium metal battery (KMB) with Prussian blue (PB) cathode in carbonate electrolyte retains 80% capacity after 200 cycles at 1C. In ether‐based electrolyte with organic cathode, it achieves 80% retention after 900 cycles at 2C. Combined synchrotron X‐ray nano‐tomography, cryogenic‐focused ion beam microscopy (Cryo‐FIB) and sputter‐down X‐ray photoelectron spectroscopy (XPS) demonstrate uniform electrodeposits, versus baseline of potassium filaments intermixed with pores and coarse SEI. Binary K 3 Bi‐K and K 2 Te‐K intermetallic supports also provide improved electrochemical performance, albeit to lesser extent. Multiscale simulation provides insight into role of support structure in adatom energetics, film nucleation, early‐stage SEI morphology and interfacial stability.

Abstract Layered oxide cathodes offer high specific capacity and operating voltage, whereas constructing a stable interface to maintain the stable operation of high‐voltage cathodes under high charge state and elevated temperature remains challenging. Herein, a double‐weak coordination strategy which triggers by single solvent and dilute is designed. The solvent tris(2,2,2‐trifluoroethyl) phosphate (TFEP) exhibits weak lithium coordination due to the partial fluorination of the alkyl chain, while the dilute ethoxy(pentafluoro)cyclo triphosphazene (PFPN) is involved in the inner solvation structure by weak lithium‐TFEP coordination and its mild lithium affinity. This double‐weak coordination increases the local anion concentration within the solvation structure, reduces the desolvation barrier of Li + , optimizes the desolvation and leads to a robust, hybrid organic–inorganic interface. Specifically, the DWCE electrolyte shows remarkable improvements in cycling stability under 60 °C for 4.7 V Li(50 µm)||NMC811 (1.84 mAh cm −2 ) cell, 4.8 and 5.0 V Li(50 µm)||LRMO (1.75 mAh cm −2 ) cells. Meanwhile, 5.2 Ah Li||LRMO pouch cell using DWCE achieves a high energy density of 495 Wh kg −1 and DWCE‐based Ah‐level pouch cell also presents significantly enhanced safety under thermal runaway condition. This work provides a novel but universal double‐weak coordination policy initiated by solvent and diluent for high energy density lithium metal batteries.

Fluorine-rich electrolytes hold promise to significantly enhance the energy and the safety of lithium metal batteries (LMBs). However, they generate acidic species, especially when lithium hexafluorophosphate (LiPF 6 ) is used as the lithium salt. This critical issue impedes their wide-scale utilization but has to date received minimum analysis. Herein, we reveal the mechanisms behind the exacerbation of HF generation in LiPF 6 -based all-fluorinated electrolytes and propose a universally applicable mitigation strategy. The screened additive Tris(trimethylsilyl)phosphate (TMSPa) reacts with HF and stabilizes PF 5 , preventing its further hydrolysis and thereby effectively reducing the HF content in fluorine-rich electrolytes. TMSPa contributes to preferentially form a conductive and protective solid electrolyte interphase (SEI), suppressing interface parasitic reactions and ensuring the structural integrity of electrode materials throughout battery cycling. The all-fluorinated electrolytes developed in this work with the addition of TMSPa (AFE-TMSPa) demonstrates a wide electrochemical window (4.6 V), high-temperature stability (up to 55°C), and enhanced safety for LMBs (flame-retardant and dendrite-suppressing). A Li metal pouch cell (7.2 Ah) employing AFE-TMSPa (NCM811 double sided cathode with a mass loading of 80.72 mg/cm 2 ), and lean electrolytes at 1.23 g Ah −1 , achieves an energy density of 572 Wh kg −1 at a 0.1 C rate. In a Li||NCM811 coin cell with a 50 µm thick Li-metal anode and a high-loading NCM811 cathode (19.8 mg cm −2 , 3.96 mAh cm −2 ), the system supports 160 stable cycles with a capacity retention of 89% at a 0.2 C charge and 0.5 C discharge rate.

Anode-Free All Solid-State Batteries The scene is the Animas Mountains range on the planet Mars. The first explorer and a mechanical rover stand facing another freezing sunrise, wind howling as a dust storm gathers strength, the thin air humming with radiation, an unconcerned landscape where anything is permitted. Powering the life support system and the rover are anode-free solid-state batteries, charting a path that others will follow in due time. More details can be found in article number 2410948 by Yixian Wang, Vikalp Raj, David Mitlin, and co-workers.

Electrodeposition of sodium metal in an anode-free battery can be dendritic. The tree at the center of the cover image represents a single crystalline dendrite, branched and complex in its morphology, originating at the support and growing towards the cathode. Its multicolor leaves are the solid electrolyte interphase (SEI) that cover the metal surface. The SEI is a complex mosaic containing crystalline sodium fluoride, sodium hydride and sodium hydroxide, as well as organic constituents. Details of this study are reported by David Mitlin, Yu-chen Karen Chen-Wiegart et al. in their Research Article (e202412550).

Electrodeposition of sodium metal in an anode-free battery can be dendritic. The tree at the center of the cover image represents a single crystalline dendrite, branched and complex in its morphology, originating at the support and growing towards the cathode. Its multicolor leaves are the solid electrolyte interphase (SEI) that cover the metal surface. The SEI is a complex mosaic containing crystalline sodium fluoride, sodium hydride and sodium hydroxide, as well as organic constituents. Details of this study are reported by David Mitlin, Yu-chen Karen Chen-Wiegart et al. in their Research Article (e202412550).

Abstract Anode‐free all solid‐state batteries (AF‐ASSBs) employ “empty” current collector with three active interfaces that determine electrochemical stability; lithium metal – Solid electrolyte (SE) interphase (SEI‐1), lithium – current collector interface, and collector – SE interphase (SEI‐2). Argyrodite Li 6 PS 5 Cl (LPSCl) solid electrolyte (SE) displays SEI‐2 containing copper sulfides, formed even at open circuit. Bilayer of 140 nm magnesium/30 nm tungsten (Mg/W‐Cu) controls the three interfaces and allows for state‐of‐the‐art electrochemical performance in half‐cells and fullcells. AF‐ASSB with NMC811 cathode achieves 150 cycles with Coulombic efficiency (CE) above 99.8%. With high mass‐loading cathode (8.6 mAh cm −2 ), AF‐ASSB retains 86.5% capacity after 45 cycles at 0.2C. During electrodeposition of Li, gradient Li‐Mg solid solution is formed, which reverses upon electrodissolution. This promotes conformal wetting/dewetting by Li and stabilizes SEI‐1 by lowering thermodynamic driving force for SE reduction. Inert refractory W underlayer is required to prevent ongoing formation of SEI‐2 that also drives electrochemical degradation. Inert Mo and Nb layers likewise protect Cu from corroding, while Li‐alloying layers (Mg, Sn) are less effective due to ongoing volume changes and associated pulverization. Mechanistic explanation for observed Li segregation within alloying Li x Mg layer is provided through mesoscale modelling, considering opposing roles of diffusivity differences and interfacial stresses.

Anode-free solid-state batteries contain no active material at the negative electrode in the as-manufactured state, yielding high energy densities for use in long-range electric vehicles. The mechanisms governing charge–discharge cycling of anode-free batteries are largely controlled by electro-chemo-mechanical phenomena at solid–solid interfaces, and there are important mechanistic differences when compared with conventional lithium-excess batteries. This Perspective provides an overview of the factors governing lithium nucleation, growth, stripping and cycling in anode-free solid-state batteries, including mechanical deformation of lithium, the chemical and mechanical properties of the current collector, microstructural effects, and stripping dynamics. Pathways for engineering interfaces to maximize performance and extend battery lifetime are discussed. We end with critical research questions to pursue, including understanding behaviour at low stack pressure, tailoring interphase growth, and engineering current collectors and interlayers. Anode-free batteries contain no active material at the negative electrode when manufactured, and this can enable them to have high energy density. This Perspective presents a critical overview of the mechanisms governing the behaviour of anode-free solid-state batteries and provides guidance to improve this type of battery.

We explore the interrelation between external pressure (0.1, 1, 10 MPa), solid electrolyte interphase (SEI) structure/morphology, and lithium metal plating/stripping behavior. To simulate anode-free lithium metal batteries (AF-LMBs) analysis was performed on “empty” Cu current collectors in standard carbonate electrolyte. Lower pressure promotes organic-rich SEI and macroscopically heterogeneous, filament-like Li electrodeposits interspersed with pores. Higher pressure promotes inorganic F-rich SEI with more uniform and denser Li film. A “seeding layer” of lithiated pristine graphene (pG@Cu) favors an anion-derived F-rich SEI and promotes uniform metal electrodeposition, enabling extended electrochemical stability at a lower pressure. State-of-the-art electrochemical performance is achieved at 1MPa: pG-enabled half-cell is stable after 300 hrs (50 cycles) at 1 mA cm -2 rate - 3 mAh cm -2 capacity (17.5 mm plated/stripped), with cycling Coulombic efficiency (CE) of 99.8%. AF-LMB cells with high mass loading NMC622 cathode (21 mg cm -2 ) undergo 200 cycles with a CE of 99.4% at C/5-charge and C/2-discharge (1C = 178 mAh/g). Density functional theory (DFT) highlights the differences in the adsorption energy of solvated-Li + onto various crystal planes of Cu (100), (110), and (111), versus lithiated/delithiated (0001) graphene, giving insight regarding the role of support surface energetics in promoting SEI heterogeneity.

In the early stages of sulfide solid-state electrolyte (SSE) research, sulfides like Li 6 PS 5 Cl (LPSCl) were primarily synthesized in laboratories using fine precursors such as Li 2 S, LiCl, and P 2 S 5 , employing meticulous synthetic procedures involving milling and sintering. This approach resulted in grams of as-synthesized SSE materials with a uniform particle size distribution and well-controlled morphology. Consequently, large-scale synthesis methods for LPSCl SSE have been developed, leading to the availability of commercial LPSCl SSE. Nonetheless, compared to lab-scale synthesis, commercial production of LPSCl SSE often yields a wide range of particle sizes and particle distributions. In-depth understanding is needed regarding how microstructural features such as the average particle size and distribution, and pore size and distribution, affect the compressed SSE's electrochemical performance. In this presentation, we investigate mechanical milling – induced microstructure changes of LPSCl SSE and their influence on electrochemical performance. Planetary mechanical milling in wet media (m-xylene) is employed to alter commercial LPSCl powder. Quantitative stereology demonstrates how extended milling progressively refines grain and pore size/distribution, increases compact density, and geometrically smoothens the SSE-Li interface. Microstructure, in turn, profoundly influences electrochemical behavior. It is shown that an optimized SSE microstructure enables state-of-the-art electrochemical performance without the need for any artificial SEI layers or other secondary modifications. Combined cryogenic focused ion beam (cryo-FIB) and X-ray photoelectron spectroscopy (XPS) demonstrate that milled microstructures promote uniform early-stage electrodeposition on foil collectors and stabilize solid electrolyte interphase (SEI) reactivity. For the first time, short-circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter "mini" symmetrical cell and cryo-FIB. Site-specific analysis highlights that the lithium metal dendrite has the following features: a) a sheet-like morphology with branching sections; b) traverses the compact intergranularly, moving around large grains rather than through them; c) fills the interparticle voids and reacts with the contacting SSE to form reduction decomposition products, i.e. the dendrite is surrounded by an SEI. Figure 1

Site-specific microstructural analysis combined with interphase design is employed to understand the origin of solid-state electrolyte failure, and to promote extended electrochemical stability. For example, stable anode-free all-solid-state battery (AF-ASSB) with an argyrodite is achieved by tuning wetting of lithium metal on “empty” copper current-collector by coating it with a thin composite film of thermodynamically stable Li 2 Te and Cu microparticles. Cryo-FIB sectioning demonstrates a dense and uniform electrodeposit, with minimal voiding or dendrites at the collector-SSE interface. Unmodified Cu current-collector promotes inhomogeneous Li electrodeposition/dissolution, leading to a thick non-uniform solid electrolyte interphase (SEI) interspersed with voids. As another example, thin intermetallic Li 2 Te–LiTe 3 bilayer derived from 2D tellurene stabilizes the Li-argyrodite SEI, allowing state-of-the-art electrochemical performance with conventional foils. The Li 2 Te–LiTe 3 bilayer impedes SSE decomposition and suppresses voiding. Unmodified Li–LPSCl undergoes reduction decomposition that extends deep into the SSE, causing reactivity-induced voids in both metal and SEI. For the first time, short-circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter "mini" symmetrical cell and cryogenic focused ion beam (cryo-FIB) electron microscopy. The branching sheet-like dendrite traverses intergranularly, filling the interparticle voids and forming an SEI around it. A separate study on dendrites in garnet LLZTO demonstrates that the compact's grain size distribution and internal porosity critically affect electrical short-circuiting, indicating the importance of local electronic properties. Lithium dendrites propagate intergranularly through regions where LLZTO grains are statistically smaller than the bulk average. Metal also accumulates in the otherwise empty pores of sintered compact present along the dendrite path. Related Work: Mechanical Milling - induced Microstructure Changes in Argyrodite LPSCl Solid-State Electrolyte Critically Affect Electrochemical Stability, Advanced Energy Materials. 2024, in-press. Dendrite Growth—Microstructure—Stress—Interrelations in Garnet Solid-State Electrolyte. Advanced Energy Materials. 2024, 2303062. https://doi.org/10.1002/aenm.202303062 Stable Anode‐Free All‐Solid‐State Lithium Battery through Tuned Metal Wetting on the Copper Current Collector. Advanced Materials . 2022 Nov 29:2206762. Tuned Reactivity at the Lithium Metal–Argyrodite Solid State Electrolyte Interphase. Advanced Energy Materials . 2023 Dec;13(46):2301338.

Solid state lithium metal batteries incorporating ceramic solid electrolytes are visioned as a promising alternative for future energy storage. However much has to be investigated regarding the electro-chemo-mechanical stability of these electrolytes. Herein we investigate the role of microstructure of garnet type ceramic solid electrolyte in lithium dendrite propagation. Clear evidence of dendrite favoring the growth along the grain boundaries is observed which suggests the role both mechanical and electronic properties of solid electrolyte plays in dendrite propagation. Furthermore, in our present study, tantalum-doped LLZTO with a nominal composition of Li6.4La3Zr1.4Ta0.6O12 was fabricated using two approaches: one involving conventional powder processing followed by reactive sintering, and the other incorporating an intermediate-stage high-energy milling step. These fabrication routes resulted in distinct microstructures, influencing their electrochemical behavior during extended cycling. The relation between the two was then analyzed in detail using surface science and bulk techniques, as well as quantitative stereology. Notably, our findings demonstrate for the first time that compact grain size distribution critically affects short-circuit failure. Lithium metal dendrites propagate intergranularly along "weak-links" in the microstructure, characterized by percolating arrays of LLZTO grains significantly smaller than the average. Additionally, lithium metal accumulates inside the pores along the dendrite's path through the compact. These observations underscore the role of enhanced electrical conductivity—specifically, electron accumulation—in the dendrite-driven failure phenomenology. Complementing the experimental findings, mechanistic modeling was employed to provide a comprehensive understanding of the interrelations between microstructure, chemo-mechanical stress, and electrochemical stability in garnet-based solid-state electrolytes. Figure 1

Lithium metal battery systems (LMBs) are being sought as an ultimate replacement to lithium ion batteries (LIBs), potentially increasing the cell energy by over fifty percent due to the high capacity and low voltage of the metal anode. Analogous improvement in energy is possible with sodium metal batteries (NMBs) and with potassium metal batteries (KMBs), where existing ion insertion anodes can be replaced by plating/stripping metal. However, in all three cases safety and performance are compromised by an unstable solid electrolyte interphase (SEI) that consumes metal ions and electrolyte, and ultimately leads to dendrites. This presentation provides a series of case studies derived from the group's LMB, NMB and KMB liquid and solid-state research on the microstructural design principles that provide for long-term cycling and fast-charge stability of metal anodes. The approaches may be categorized as the following: a) design of plating/stripping supports and templates with tuned geometry and functionality; b) design of secondary interlayers placed between the metal anode and the separator; and c) design of multifunctional hybrid separators to replace the conventional polymer separators employed with LIBs. It is demonstrated that despite appearing distinct, the efficacy of each in enabling electrochemical stability originates from three fundamental features that are directly interrelated. The wetting behavior of the electrolyte on the anode must be optimized, the wetting/stripping behavior of the metal anode on the current collector must be controlled, and a geometrically and chemically modified SEI must be established. Simultaneously achieving all three leads to stable plating/stripping, while missing even one leads to rapid dendrite growth. Cryogenic FIB cross sections and cryo-TEM are combined to yield new insight regarding film wetting behavior and early dendrite formation in optimized versus baseline specimens, analyzing growth in several representative electrolytes.

Abstract This study examines how current collector support chemistry (sodiophilic intermetallic Na 2 Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm −2 , 0.5–3 mA cm −2 ) representative of commercially relevant mass loading in anode‐free sodium metal battery (AF‐SMBs) are analyzed. Synchrotron X‐ray nanotomography and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) are combined with cryogenic ion beam (cryo‐FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te−Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modeling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability.

Abstract This study examines how current collector support chemistry (sodiophilic intermetallic Na 2 Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm −2 , 0.5–3 mA cm −2 ) representative of commercially relevant mass loading in anode‐free sodium metal battery (AF‐SMBs) are analyzed. Synchrotron X‐ray nanotomography and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) are combined with cryogenic ion beam (cryo‐FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te−Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modeling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability.

Stable anode-free all-solid-state battery (AF-ASSB) with sulfide-based solid-electrolyte (SE) (argyrodite Li 6 PS 5 Cl, LPSCl) is achieved by tuning wetting of lithium metal on “empty” copper current-collector. Lithiophilic 1 μm Li 2 Te is synthesized by exposing the collector to tellurium vapor, followed by in-situ Li activation during the first charge. The Li 2 Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency (CE). During continuous plating experiments using half-cells (1 mA cm -2 ), the accumulated thickness of electrodeposited Li on Li 2 Te-Cu is more than 70 μm, which is the thickness of Li foil counter-electrode. Full AF-ASSB with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryo-FIB sectioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector-SE interface. Electrodissolution is uniform and complete, with Li 2 Te remaining structurally stable and adherent. By contrast, unmodified Cu current-collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive “dead metal”, dendrites that extend into SE, and thick non-uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory and mesoscale calculations provide complementary insight regarding nucleation-growth behavior. Unlike for conventional liquid-electrolyte metal batteries, the role of current collector/support lithiophilicy has not been explored for emerging AF-ASSBs.

Sodiophilic micro-composite films of sodium-chalcogenide intermetallics (Na 2 Te and Na 2 S) and Cu particles are fabricated onto commercial copper foam current collectors (Na 2 Te@CF and Na 2 S@CF). For the first time a controllable capacity thermal infusion process is demonstrated. Enhanced wetting by the metal electrodeposition leads to state-of-the-art electrochemical performance. For example, Na 2 Te@CF-based half-cells demonstrate stable cycling at 6 mA cm -2 and 6 mAh cm -2 , corresponding to 54 μm of Na electrodeposited/electrodissolved by geometric area. Sodium metal battery (SMB, NMB) cells with Na 3 V 2 (PO 4 ) 3 (NVP) cathodes are stable at 30C (7 mA cm -2 ) and for 10,000 cycles at 5C and 10C. Cross-sectional cryogenic focused ion beam (cryo-FIB) microscopy details deposited and remnant dissolved microstructures. Sodium metal deposited onto Na 2 Te@CF is dense, smooth, and free of dendrites or pores. On unmodified copper foam, sodium grows in a filament-like manner, not requiring cycling to achieve this geometry. Substrate-metal interaction critically affects the metal-electrolyte interface, namely the thickness and morphology of the solid electrolyte interphase (SEI). Density functional theory (DFT) and mesoscale simulations provide insight into support-adatom energetics, nucleation response, and early-stage morphological evolution. On Na 2 Te sodium atomic dispersion is thermodynamically more stable than isolated clusters, leading to conformal adatom coverage of the surface.

Thin intermetallic Li 2 Te–LiTe 3 bilayer (0.75 mm) derived from 2D tellurene stabilizes solid electrolyte interphase (SEI) of lithium metal and argyrodite (LPSCl, Li 6 PS 5 Cl) solid-state electrolyte (SSE). Tellurene is loaded onto standard battery separator and reacted with lithium through single-pass mechanical rolling, or transferred directly to SSE surface by pressing. State-of-the-art electrochemical performance is achieved, e.g. symmetric cell stable for 300 cycles (1800 hours) at 1 mA cm -2 and 3 mAh cm -2 (25% DOD, 60 mm foil). Cryo-FIB sectioning and Raman mapping demonstrate that Li 2 Te–LiTe 3 bilayer impedes SSE decomposition. The unmodified Li–LPSCl interphase is electrochemically unstable with geometrically heterogeneous reduction decomposition reaction front that extends deep into the SSE. Decomposition drives voiding in Li metal due to its high flux to the reaction front, as well as voiding in the SSE due to the associated volume changes. Analysis of cycled SSEs found no evidence for pristine (unreacted) lithium metal filaments/dendrites, implying failure driven by decomposition phases with sufficient electrical conductivity that span electrolyte thickness. Density Functional Theory (DFT) calculations clarify thermodynamic stability, interfacial adhesion, and electronic transport properties of interphases, while mesoscale modeling examines interrelations between reaction front heterogeneity (SEI heterogeneity), current distribution and localized chemo-mechanical stresses.

Lithium metal is regarded as the “holy grail” of lithium-ion battery anodes due to its exceptionally high theoretical capacity (3800 mAh g –1 ) and lowest possible electrochemical potential (−3.04 V vs Li/Li + ); however, lithium suffers from the dendritic formation that leads to parasitic reactions and cell failure. In this work, we stabilize fast-charging lithium metal plating/stripping with dual-function alloying M -nitrate additives ( M: Ag, Bi, Ga, In, and Zn). First, lithium metal reduces M, forming lithiophilic alloys for dense Li nucleation. Additionally, nitrates form ionically conductive and mechanically stable Li 3 N and LiN x O y, enhancing Li-ion diffusion through the passivation layer. Notably, Zn-protected cells demonstrate electrochemically stable Li||Li cycling for 750+ cycles (2.0 mA cm –2 ) and 140 cycles (10.0 mA cm –2 ). Moreover, Zn-protected Li||Lithium Iron Phosphate full-cells achieve 134 mAh g –1 (89.2% capacity retention) after 400 cycles (C/2). This work investigates a promising solution to stabilize lithium metal plating/stripping for fast-charging lithium metal batteries.

Solid-State Electrolytes Driven to spawn, salmon leave the ocean and swim upstream through flowing rivers and around stones and other obstacles in their path. Driven by charging voltage, lithium ions leave the cathode and diffuse “upstream” through the solid electrolyte while obstructed by pores, roughened interfaces, and grain boundaries. In article number 2304530, Yixian Wang, Hongchang Hao, David Mitlin, and co-workers demonstrate that controlling the distribution of such obstacles by mechanical milling is critical for electrochemical stability of all solid-state batteries.

Abstract Aluminum oxide (Al 2 O 3 ) nanopowder is spin‐coated onto both sides of commercial polypropene separator to create artificial solid‐electrolyte interphase (SEI) and artificial cathode electrolyte interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm 2 –0.5 mAh/cm 2 and 3.0 mA/cm 2 –0.5 mAh/cm 2 . Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo‐stage focused ion beam (cryo‐FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina‐modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal – SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.

Abstract Aluminum oxide (Al 2 O 3 ) nanopowder is spin‐coated onto both sides of commercial polypropene separator to create artificial solid‐electrolyte interphase (SEI) and artificial cathode electrolyte interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm 2 –0.5 mAh/cm 2 and 3.0 mA/cm 2 –0.5 mAh/cm 2 . Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo‐stage focused ion beam (cryo‐FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina‐modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal – SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.