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.

This work elucidates the mechanism by which lithium borohydride (LiBH4) doping into argyrodite-type Li6PS5Cl (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 2.6mA 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 PS4 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 Li3P/LiBH4/Li2S 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 Li3P/Li2S is substantially thicker, generating localized stresses that promote interfacial cracking while cycling.

Lithium metal dendrite penetration and interfacial instabilities are critical challenges that hinder the widespread adoption of all-solid-state batteries (ASSBs). In this work, we systematically investigate the impact of viscoplastic deformation on these mechanisms, using Li6PS5Cl electrolyte as an example. This study focuses on evaluating rate-dependent behavior by applying moderate stack pressures with custom-designed electrochemical cycling protocols that employ zero-current holds and sinusoidal-like cycling. The highest critical current density achieved in our study was 4.8 mA/cm2. Our analysis indicates that relatively slow lithium creep mitigates interfacial void formation and enhances the critical current density and cycle life. It also indicates that the stresses in the vicinity of these voids are well above the reported yield stress for lithium metal. The overall findings highlight the critical role of mechanical properties in the stability of the electrolyte-metal interface and demonstrate that leveraging viscoplasticity can substantially enhance the sulfide-based ASSB cycling performance.

Alkali metal negative electrodes in solid-state batteries (SSBs) undergo mechanical deformation during cycling, for which an understanding of their physical metallurgy is critical. Here, we study the link between microstructure and plastic deformation in lithium and sodium. Grain size is controlled through deformation processing, and etching methods are developed to reveal grain boundaries, subgrain boundaries, and dislocation structures. Hall-Petch strengthening with decreasing grain size occurs in both metals. Creep rate in lithium is grain-size-independent above the subgrain size, but increases at small grain sizes where diffusional creep dominates. Oxide dispersion-strengthened behavior is observed in Li. At length scales below the subgrain size, strength increases and creep rates decrease due to dislocation starvation. Solid-state electrochemical cell tests in which lithium of differing foil thickness is stripped under pressure validates length-scale effects. Overall, this work provides a physical metallurgy framework for alkali metal deformation and offers design principles for advanced SSBs.

We report a method for promoting electrochemical stability in garnet Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) solid-state electrolyte (SSE) based on composite two-phase oxide-oxide microstructure. Grain boundary precipitation of controlled distribution of amorphous zirconium oxide (ZrO 2 ) microparticles is achieved through addition of reactive tantalum carbide (TaC). During ambient atmosphere sintering the carbide decomposes through an in-situ reaction, the “extra” Ta substituting for Zr within the LLZTO lattice. Density functional theory (DFT) calculations identify thermodynamically favorable reaction path and show how substituting Ta 5+ at Zr 4+ sites affect the crystal structure, as well as bulk ionic and electronic conductivity. Quantitative stereology highlights that zirconia also acts as a sintering aid, reducing compact porosity. Cryogenic FIB-SEM and fractography analysis of cycled SSEs illustrates that near-universally observed intergranular Li-metal dendrite propagation is suppressed by the two-phase microstructure, favoring transgranular dendrites instead. Importantly, DFT demonstrates that compared to LLZTO surface, the ZrO 2 surface per se is less electronically conductive and does not trap excess electrons. This is a key reason for the significant improvement in the electrochemical properties over the single-phase baseline. Grain boundary zirconia-modified garnet solid-state electrolyte. Nature Materials. 2025 Oct 15:1-0.

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.

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.

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.

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.

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.

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.]

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.

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.

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 (LiPF6) 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 LiPF6-based allfluorinated electrolytes and propose a universally applicable mitigation strategy. The screened additive Tris (trimethylsilyl)phosphate (TMSPa) reacts with HF and stabilizes PF5, 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 degrees 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/cm2), 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 mu m 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.

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.

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 Li6PS5Cl (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 LixMg layer is provided through mesoscale modelling, considering opposing roles of diffusivity differences and interfacial stresses.

We employed accumulative roll bonding to fabricate self-standing metallurgical composite of in situ formed alkaline potassium-bismuth-telluride intermetallic K2(Bi2/6Te3/6Vac1/6) embedded in potassium metal. This newly discovered thermodynamically stable potassiophilic crystal, termed "KBT", is fcc antifluorite with K2Te 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 K3Bi-K and K2Te-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.

We report a method for promoting electrochemical stability in garnet Li6.4La3Zr1.4Ta0.6O12 solid-state electrolyte based on a composite two-phase oxide-oxide microstructure. Grain boundary precipitation of the controlled distribution of amorphous zirconium oxide microparticles is achieved through the addition of reactive tantalum carbide. During ambient-atmosphere sintering, the carbide decomposes through an in situ reaction, the 'extra' Ta substituting for Zr within the Li6.4La3Zr1.4Ta0.6O12 lattice. Density functional theory (DFT) calculations identify a thermodynamically favourable reaction path and show how substituting Ta5+ at Zr4+ sites affects the crystal structure as well as bulk ionic and electronic conductivities. Quantitative stereology highlights that zirconia also acts as a sintering aid, reducing compact porosity. Cryogenic focused-ion-beam scanning electron microscopy and fractography analysis of cycled solid-state electrolytes illustrates that near-universally observed intergranular Li-metal dendrite propagation is suppressed by the two-phase microstructure, favouring transgranular dendrites instead. Importantly, DFT demonstrates that compared with the Li6.4La3Zr1.4Ta0.6O12 surface, the zirconium oxide surface per se is less electronically conductive and does not trap excess electrons to reduce Li ions. This is a key reason for the substantial improvement in the electrochemical properties over the single-phase baseline.