Suppressing Lithium Dendrite Growth by Metallic Coating on a Separator

Lithium (Li) metal is one of the most promising candidates for the anode in high‐energy‐density batteries. However, Li dendrite growth induces a significant safety concerns in these batteries. Here, a multifunctional separator through coating a thin electronic conductive film on one side of the conventional polymer separator facing the Li anode is proposed for the purpose of Li dendrite suppression and cycling stability improvement. The ultrathin Cu film on one side of the polyethylene support serves as an additional conducting agent to facilitate electrochemical stripping/deposition of Li metal with less accumulation of electrically isolated or “dead” Li. Furthermore, its electrically conductive nature guides the backside plating of Li metal and modulates the Li deposition morphology via dendrite merging. In addition, metallic Cu film coating can also improve thermal stability of the separator and enhance the safety of the batteries. Due to its unique beneficial features, this separator enables stable cycling of Li metal anode with enhanced Coulombic efficiency during extended cycles in Li metal batteries and increases the lifetime of Li metal anode by preventing short‐circuit failures even under extensive Li metal deposition.     

Controlling Solvation and Solid-Electrolyte Interphase Formation to Enhance Lithium Interfacial Kinetics at Low Temperatures

Operation of lithium-based batteries at low temperatures (<0 °C) is challenging due to transport limitations as well as sluggish Li⁺ kinetics at the electrode interface. The complicated relationships among desolvation, charge transfer, and transport through the solid electrolyte interphase (SEI) at low temperatures are not well understood, hindering electrolyte development. Here, an ether/hydrofluoroether and fluoroethylene carbonate (FEC)-based ternary solvent electrolyte is developed to improve Li cycling at low temperatures (Coulombic efficiency of 93.3% at -40 °C), and the influence of the local solvation structure on interfacial Li⁺ kinetics and SEI chemistry is further revealed. The hydrofluoroether cosolvent allows for modulation of the solvation structure, thereby enabling facile Li⁺ desolvation while forming an inorganic-rich SEI, which are both beneficial for lowering Li⁺ kinetic barriers at the interface. This cosolvent also increases the oxidative stability of the electrolyte to over 4.0 V versus Li/Li⁺, thereby enabling cycling of NMC-based full cells at −40 °C. This study advances the understanding of the influence of Li⁺ solvation structure, SEI chemistry, and interfacial Li⁺ kinetics on Li electrochemistry at low temperatures, providing new design considerations for creating effective low-temperature electrolyte systems.     

Electrolyte Interphase Built from Anionic Covalent Organic Frameworks for Lithium Dendrite Suppression

Lithium (Li) metal batteries hold considerable promise for numerous energy-dense applications. However, the dendritic Li anode produced during Li⁺/Li deposition-stripping endangers battery safety and shortens cycle lifespan. Herein, an electrolyte interphase built from 2D anionic covalent organic frameworks (ACOF) is coated on Li for dendrite suppression. The ACOF with Li⁺-affinity facilitates rapid and exclusive passage of Li-ions from the electrolyte, yielding near-unity Li⁺ transference number (0.82) and ionic conductivity beyond 3.7 mS cm^-1 at the interphase. Such high transport efficiency of Li-ions can fundamentally circumvent the Li⁺ deficiency that results in dendrite formation. Pairing the ACOF-coated Li against a high-voltage LiCoO₂ cathode (4.5 V) achieves exceptional cycle stability, mitigated polarization, as well as improved rate capability. Accordingly, this strategy vastly expands the pool of electrolyte interphases that can be used for coating and protecting Li anode.     

Strategies in Structure and Electrolyte Design for High-Performance Lithium Metal Batteries

Lithium metal is the “holy grail” anode for next-generation high-energy rechargeable batteries due to its high capacity and lowest redox potential among all reported anodes. However, the practical application of lithium metal batteries (LMBs) is hindered by safety concerns arising from uncontrollable Li dendrite growth and infinite volume change during the lithium plating and stripping process. The formation of stable solid electrolyte interphase (SEI) and the construction of robust 3D porous current collectors are effective approaches to overcoming the challenges of Li metal anode and promoting the practical application of LMBs. In this review, four strategies in structure and electrolyte design for high-performance Li metal anode, including surface coating, porous current collector, liquid electrolyte, and solid-state electrolyte are summarized. The challenges, opportunities, perspectives on future directions, and outlook for practical applications of Li metal anode, are also discussed.     

Inorganic Filler Enhanced Formation of Stable Inorganic-Rich Solid Electrolyte Interphase for High Performance Lithium Metal Batteries

Lithium metal (LM) is a promising anode material for next generation lithium ion based electrochemical energy storage devices. Critical issues of unstable solid electrolyte interphases (SEIs) and dendrite growth however still impede its practical applications. Herein, a composite gel polymer electrolyte (GPE), formed through in situ polymerization of pentaerythritol tetraacrylate with fumed silica fillers, is developed to achieve high performance lithium metal batteries (LMBs). As evidenced theoretically and experimentally, the presence of SiO₂ not only accelerates Li⁺ transport but also regulates Li⁺ solvation sheath structures, thus facilitating fast kinetics and formation of stable LiF-rich interphase and achieving uniform Li depositions to suppress Li dendrite growth. The composite GPE-based Li||Cu half-cells and Li||Li symmetrical cells display high Coulombic efficiency (CE) of 90.3% after 450 cycles and maintain stability over 960 h at 3 mA cm⁻² and 3 mAh cm⁻², respectively. In addition, Li||LiFePO₄ full-cells with a LM anode of limited Li supply of 4 mAh cm⁻² achieve capacity retention of 68.5% after 700 cycles at 0.5 C (1 C = 170 mA g⁻¹). Especially, when further applied in anode-free LMBs, the carbon cloth||LiFePO₄ full-cell exhibits excellent cycling stability with an average CE of 99.94% and capacity retention of 90.3% at the 160th cycle at 0.5 C.     

Dynamic Ion Sieve as the Buffer Layer for Regulating Li+ Flow in Lithium Metal Batteries

How to realize uniform Li⁺ flow is the key to achieve even Li deposition for lithium metal batteries (LMBs). In this study, a concept of dynamic ion sieve is proposed to design the buffer layer nearby Li anode surface to regulate Li⁺ spatial arrangement by introducing tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (TMPB) into the carbonate electrolyte. The buffer layer induced by TMP⁺ can adjust the velocity of arriving solvated Li⁺ that gives solvated Li⁺ sufficient time to redistribute and accumulate on Li anode surface, resulting in a uniform and higher concentrated Li⁺ flow. Besides, TFSI⁻ can participate in the generation of inorganic component-rich solid electrolyte interphase (SEI) with Li₃N, which can facilitate the Li⁺ conductivity of SEI. Consequently, the stable and uniform Li deposition can be obtained, achieving the excellent cycling performance up to 1000 h at 0.5 mA cm⁻² in the Li||Li symmetric cell. Besides, the Li||NCM622 full cell also possesses excellent cycling stability with a high-capacity retention rate of 66.7% after 300 cycles.     

Regulating Na-ion Solvation in Quasi-Solid Electrolyte to Stabilize Na Metal Anode

Sodium metal batteries are promising for cost-effective energy storage, however, the sluggish ion transport in electrolytes and detrimental sodium-dendrite growth stall their practical applications. Herein, a cross-linking quasi-solid electrolyte with a high ionic conductivity of 1.4 mS cm⁻¹ at 25 °C is developed by in-situ polymerizing poly (ethylene glycol) diacrylate-based monomer. Benefiting from the refined solvation structure of Na⁺ with a much lower desolvation barrier, random Na⁺ diffusion on the Na surface is restrained, so that the Na dendrite formation is suppressed. Consequently, symmetrical Na||Na cells employing the electrolyte can be cycled >2000 h at 0.1 mA cm⁻². Na₃V₂(PO₄)₃||Na batteries reveal a high discharge specific capacity of 66.1 mAh g⁻¹ at 15 C and demonstrate stable cycling over 1000 cycles with a capacity retention of 83% at a fast rate of 5 C.     

Printable Solid Electrolyte Interphase Mimic for Antioxidative Lithium Metal Electrodes

Despite the ever‐growing demand for Li metals as next‐generation Li battery electrodes, little attention has been paid to their oxidation stability, which must be achieved for practical applications. Here, a new class of printable solid electrolyte interphase mimic (pSEI) for antioxidative Li metal electrodes is presented. The pSEI (≈1 µm) is directly fabricated on a thin Li metal electrode (25 µm) by processing solvent‐free, UV polymerization‐assisted printing, exhibiting its manufacturing simplicity and scalability. The pSEI is rationally designed to mimic a typical SEI comprising organic and inorganic components, in which ethoxylated trimethylolpropane triacrylate and diallyldimethylammonium bis(trifluoromethanesulfonyl)imide are introduced as an organic mimic (acting as a moisture‐repellent structural framework) and inorganic mimic (allowing facile Li‐ion transport/high Li⁺ transference number), respectively. Driven by the chemical/architectural uniqueness, the pSEI enables the thin Li metal electrode to show exceptional antioxidation stability and reliable full cell performance after exposure to humid environments.     

Fluorinated Bifunctional Solid Polymer Electrolyte Synthesized under Visible Light for Stable Lithium Deposition and Dendrite-Free All-Solid-State Batteries

Solid polymer electrolytes (SPEs) that can offer flexible processability, highly tunable chemical functionality, and cost effectiveness are regarded as attractive alternatives for liquid electrolytes (LE) to address their safety and energy density limitations. However, it remains a great challenge for SPEs to stabilize Li⁺ deposition at the electrolyte–electrode interface and impede lithium dendrite proliferation compared with LE-based systems. Herein, a design of solid-state fluorinated bifunctional SPE (FB-SPE) that covalently tethers fluorinated chains with polyether-based segments is proposed and synthesized via photo-controlled radical polymerization (photo-CRP). In contrast to the conventional non-fluorinated polyether-derived SPEs, FB-SPE is able to provide conducting Li⁺ transport pathways up to ≈5.0 V, while simultaneously forming a Li F interaction that can enhance Li anode compatibility and prevent Li dendrites growth. As a result, the FB-SPE exhibits outstanding cycling stability in Li||Li symmetrical cells of over 1500 operating hours at as high current density as 0.2 mA cm⁻². A thin and uniform Li deposition layer and LiF-rich SEI at the surface of Li anode are found, and stable cycling with average coulombic efficiencies of 99% is demonstrated in Li||LFP and Li||NCM all-solid-state batteries based on such bifunctional fluorinated SPEs. The interesting fluorine effect and effective self-suppression of lithium dendrites will inform rational molecular design of novel electrolytes and practical development of all-solid-state Li metal batteries.     

Regulating the Water Molecular in the Solvation Structure for Stable Zinc Metal Batteries

Rechargeable aqueous zinc batteries are promising energy storage devices because of their low cost, high safety, and high energy density. However, their performance is plagued by the unsatisfied cyclability due to the dendrite growth and hydrogen evolution reaction (HER) at the Zn anode. Herein, it is demonstrated that the concentrated hybrid aqueous/non-aqueous ZnCl₂ electrolytes constitute a peculiar chemical environment for not only the Zn-ions but also water molecules. The high concentration of chloride ions substitutes the H₂O molecular in the solvation structure of Zn²⁺, while the acetonitrile further interacts with H₂O to decrease its activity. The hybrid electrolytes both inhibit the dendrite formation and HER, enabling an ultrahigh average Coulombic efficiency of 99.9% in the Zn||Cu half-cell and a highly reversible Zn plating/stripping with a low overpotential of 21 mV. Using this hybrid electrolyte, the Zn||polytriphenylamine (PTPAn) full cell deliveres a high discharge capacity of 110 mAh g⁻¹, a high power density of 9200 W kg⁻¹ at 100 °C and maintains 85% of the capacity for over 6000 cycles at 10 °C. This study provides a deep understanding between the solvation structure and columbic efficiency of Zn anode, thus inspiring the development for stable Zn batteries.     

Nitrate Additives Coordinated with Crown Ether Stabilize Lithium Metal Anodes in Carbonate Electrolyte

Lithium metal anodes (LMAs) are promising for next-generation batteries but have poor compatibility with the widely used carbonate-based electrolytes, which is a major reason for their severe dendrite growth and low Coulombic efficiency (CE). A nitrate additive to the electrolyte is an effective solution, but its low solubility in carbonates is a problem that can be solved using a crown ether, as reported. A rubidium nitrate additive coordinated with 18-crown-6 crown ether stabilizes the LMA in a carbonate electrolyte. The coordination promotes the dissolution of NO₃⁻ ions and helps form a dense solid electrolyte interface that is Li₃N-rich which guides uniform Li deposition. In addition, the Rb (18-crown-6)⁺ complexes are adsorbed on the dendrite tips, shielding them from Li deposition on the dendrite tips. A high CE of 97.1% is achieved with a capacity of 1 mAh cm⁻² in a half cell, much higher than when using the additive-free electrolyte (92.2%). Such an additive is very compatible with a nickel-rich ternary cathode at a high voltage, and the assembled full battery with a cathode material loading up to 10 mg cm⁻² shows an average CE of 99.8% over 200 cycles, indicating a potential for practical use.     

Non-Flammable Electrolyte with Lithium Nitrate as the Only Lithium Salt for Boosting Ultra-Stable Cycling and Fire-Safety Lithium Metal Batteries

Lithium metal batteries (LMBs) attract considerable attention for their incomparable energy density. However, safety issues caused by uncontrollable lithium dendrites and highly flammable electrolyte limit large-scale LMBs applications. Herein, a low-cost, thermally stable, and low environmentally-sensitive lithium nitrate (LiNO₃) is proposed as the only lithium salt to incorporate with nonflammable triethyl phosphate and fluoroethylene carbonate (FEC) co-solvent as the electrolyte anticipated to enhance the performance of LMBs. Benefiting from the presence of NO₃⁻ and FEC with strong solvation effect and easily reduced ability, a Li₃N–LiF-rich stable solid electrolyte interphase is constructed. Compared to commercial electrolytes, the proposed electrolyte has a high Coulombic efficiency of 98.31% in Li-Cu test at 1 mA cm⁻² of 1.0 mAh cm⁻² with dendrite-free morphology. Additionally, the electrolyte system shows high voltage stability and cathode electrolyte interphase film-forming properties with stable cycling performances, which exhibit outstanding capacity retention rates of 96.39% and 83.74% after 1000 cycles for LFP//Li and NCM811//Li, respectively. Importantly, the non-flammable electrolyte delays the onset of combustion in lithium metal soft pack batteries by 255 s and reduces the peak heat release by 21.02% under the continuous external high-temperature heating condition. The novel electrolyte can contribute immensely to developing high-electrochemical-performance and high-safety LMBs.     

Electrolytes Enriched by Crown Ethers for Lithium Metal Batteries

Lithium (Li) metal battery is considered the most promising next-generation battery due to its low potential and high theoretical capacity. However, Li dendrite growth causes serious safety problems. Herein, the 15-Crown-5 (15-C-5) is reported as an electrolyte additive based on solvation shell regulation. The strong complex effect between Li⁺ ion and 15-C-5 can reduce the concentration of Li ions on the electrode surface, thus changing the nucleation, and repressing the growth of Li dendrites in the plating process. Significantly, the strong coordination of Li⁺/15-C-5 would be able to make them aggregate around the Li crystal surface, which could form a protective layer and favor the formation of a smooth and dense solid electrolyte interphase with high toughness and Li⁺ ion conductivity. Therefore, the electrolyte system with 2.0 wt% 15-C-5 achieves excellent electrochemical performance with 170 cycles at 1.0 mA cm⁻² with capacity of 0.5 mA h cm⁻² in symmetric Li|Li cells. The obviously enhanced cycle and rate performance are also achieved in Li|LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) full cells. The 15-C-5 demonstrates to be a promising additive for the electrolytes toward safe and efficient Li metal batteries.     

Stable Li Metal Anode Enabled by Simultaneous Regulation of Electrolyte Solvation Chemistry and The Solid Electrolyte Interphase

The application of Li metal batteries is hindered by the uncontrollable growth of Li dendrites due to the lack of control over Li ion transfer and the formation of solid electrolyte interphase (SEI). Herein, polypropylene (PP) separator modified with acyclic polyaminoborane (PAB, (NH₂-BH₂)_n) and polyiminoborane (PIB, (NH═BH)_n) is developed to regulate electrolyte solvation chemistry and simultaneously facilitate the construction of robust SEI. The mediating effect of PAB and PIB promotes favorable formation of (O)₂ Li⁺ N to weaken the Li bonds between Li ion and solvent in the electrolyte, which homogenizes Li ion diffusion and reduces the desolvation barrier of Li ions. Additionally, the increase of anions content in the solvation sheath and the reaction between Li metal and PAB and PIB can induce the formation of [LiNBH]_n-enhanced SEI enriched with LiF and Li₃N that have Li ion conductivity and mechanical strength to tolerate the volume change of Li metal anode. Therefore, the symmetric cell exhibits a cycling lifetime of over 4000 h.     

Fast Li+ Transport via Silica Network-Driven Nanochannels in Ionomer-in-Framework for Lithium Metal Batteries

For the development of all-solid-state lithium metal batteries (LMBs), a high-porous silica aerogel (SA)-reinforced single-Li⁺ conducting nanocomposite polymer electrolyte (NPE) is prepared via two-step selective functionalization. The mesoporous SA is introduced as a mechanical framework for NPE as well as a channel for fast lithium cation migration. Two types of monomers containing weak-binding imide anions and Li⁺ cations are synthesized and used to prepare NPEs, where these monomers are grafted in SA to produce SA-based NPEs (SANPEs) as ionomer-in-framework. This hybrid SANPE exhibits high ionic conductivities (≈10⁻³ S cm⁻¹), high modulus (≈10⁵ Pa), high lithium transference number (0.84), and wide electrochemical window (>4.8 V). The resultant SANPE in the lithium symmetric cell possesses long-term cyclic stability without short-circuiting over 800 h under 0.2 mA cm⁻². Furthermore, the LiFePO₄|SANPE|Li solid-state batteries present a high discharge capacity of 167 mAh g⁻¹ at 0.1 C, good rate capability up to 1 C, wide operating temperatures (from −10 to 40 °C), and a stable cycling performance with 97% capacity retention and 100% coulombic efficiency after 75 cycles at 1 C and 25 °C. The SANPE demonstrates a new design principle for solid-state electrolytes, allowing for a perfect complex between inorganic silica and organic polymer, for high-energy-density LMBs.     

Unprecedented Improvement of Single Li‐Ion Conductive Solid Polymer Electrolyte Through Salt Additive

Solid‐state lithium metal (Li°) batteries (SSLMBs) are believed to be the most promising technologies to tackle the safety concerns and the insufficient energy density encountered in conventional Li‐ion batteries. Solid polymer electrolytes (SPEs) inherently own good processability and flexibility, enabling large‐scale preparation of SSLMBs. To minimize the growth of Li° dendrites and cell polarization in SPE‐based SSLMBs, an additive‐containing single Li‐ion conductive SPE is reported. The characterization results show that a small dose of electrolyte additive (2 wt%) substantially increases the ionic conductivity of single Li‐ion conductive SPEs as well as the interfacial compatibility between electrode and SPE, allowing the cycling of SPE‐based cells with good electrochemical performance. This work may provide a paradigm shift on the design of highly cationic conductive electrolytes, which are essential for developing safe and high‐performance rechargeable batteries.     

Establishing the Preferential Adsorption of Anion-Dominated Solvation Structures in the Electrolytes for High-Energy-Density Lithium Metal Batteries

The practical application of Li metal batteries (LMBs) is severely hindered by the unstable solid electrolyte interface (SEI). In this work, it is revealed that the unstable SEI mainly originates from the kinetic instability of Li⁺-solvation structures in the electrolyte which can result in continuous electrolyte decomposition and nonuniform Li deposition. To address this issue, preferential adsorption of anion-dominated solvation complexes (A-Coms) are established by integrating preferentially adsorbed anions (NO₃⁻ and Li₂S₈) into the Li⁺-solvation structures. In these structures, the locations of the lowest unoccupied molecular orbital energy level shift from solvents to anions, rendering a relieved electrolyte decomposition and an anion-derived SEI formation. Meanwhile, the anions in the A-coms preferentially adsorb on the Li metal surfaces due to their stronger chemisorption capability toward lithium metal anodes (LMAs) compared to the solvent molecules, effectively shielding solvent molecules from parasitic reaction with LMAs. Furthermore, the anion-derived SEI exhibits high Li-ion conductivity and low Li atom adhesion energy, which can facilitate uniform Li deposition. Consequently, this electrolyte can enable a high Li plating/stripping Coulombic efficiency of 98.5% over 500 cycles and a stable cycling under realistic testing conditions with a high-energy-density of 310 W h kg⁻¹ based on a full cell configuration.     

Lithiophilic MXene-Guided Lithium Metal Nucleation and Growth Behavior

The positive effects of a lithiophilic substrate on the electrochemical performance of lithium metal anodes are confirmed in several reports, while the understanding of lithiophilic substrate-guided lithium metal nucleation and growth behavior is still insufficient. In this study, the effect of a lithiophilic surface on lithium metal nucleation and growth behaviors is investigated using a large-area Ti₃C₂T_x MXene substrate with a large number of oxygen and fluorine dual heteroatoms. The use of the MXene substrate results in a high lithium-ion concentration as well as the formation of uniform solid–electrolyte-interface (SEI) layers on the lithiophilic surface. The solid–solid interface (MXene-SEI layer) significantly affects the surface tension of the deposited lithium metal nuclei as well as the nucleation overpotential, resulting in the formation of uniformly dispersed lithium nanoparticles ( ≈ 10–20 nm in diameter) over the entire MXene surface. The primary lithium nanoparticles preferentially coalesce and agglomerate into larger secondary particles while retaining their primary particle shapes. Subsequently, they form close-packed structures, resulting in a dense metal layer composed of particle-by-particle microstructures. This distinctive lithium metal deposition behavior leads to highly reversible cycling performance with high Columbic efficiencies >  99.0% and long cycle lives of over 1000 cycles.     

Tuning the Electrolyte Solvation Structure to Suppress Cathode Dissolution,Water Reactivity,and Zn Dendrite Growth in Zinc-Ion Batteries

The cycle life of aqueous zinc-ion batteries (ZIBs) is limited by the notable challenges of cathode dissolution, water reactivity, and zinc dendrites. Here, it is demonstrated that by tuning the electrolyte solvation structure, the issues for both the electrodes and the electrolyte can be addressed simultaneously. Specifically, a fire-retardant triethyl phosphate (TEP) is demonstrated as a cosolvent with strong solvating ability in a nonaqueous/aqueous hybrid electrolyte. The TEP features a higher donor number (26 kcal mol⁻¹) than H₂O (18 kcal mol⁻¹), preferring to form a TEP occupied inner solvation sheath around Zn²⁺ and strong hydrogen bonding with H₂O. The TEP coordinated electrolyte structure can inhibit the reactivity of H₂O with V₂O₅ and leads to a robust polymeric-inorganic interphase (poly-ZnP₂O₆ and ZnF₂) on zinc anode effectively preventing the dendrite growth and parasitic water reaction. With such an optimized electrolyte, the Zn/Cu cells perform high average Coulombic efficiency of 99.5%, and the full cell with a low capacity ratio of Zn:V₂O₅ (2:1) and lean electrolyte (11.5 g Ah⁻¹) delivers a reversible capacity of 250 mAh g⁻¹ for over 1000 cycles at 5 A g⁻¹. This study highlights the promise of a successful electrolyte regulation strategy for the development of high-performance and practical ZIBs.     

A Self-Limited Free-Standing Sulfide Electrolyte Thin Film for All-Solid-State Lithium Metal Batteries

All-solid-state (ASS) lithium metal batteries (LMBs) are considered the most promising next-generation batteries due to their superior safety and high projected energy density. To access the practically desired high energy density of ASS LMBs, an ultrathin solid-state electrolyte (SSE) film with fast ion-transport capability presents as an irreplaceable component to reduce the proportion of inactive materials in ASS batteries. In this contribution, an ultrathin (60  µ m), flexible, and free-standing argyrodite (Li₆PS₅Cl) SSE film is designed through a self-limited strategy. A chemically compatible cellulose membrane is employed as the self-limiting skeleton that not only defined the thinness of the sulfide SSE film but also strengthened its mechanical properties. The ionic conductivity of the SSE film reaches up to 6.3 × 10⁻³ S cm⁻¹ at room temperature, enabling rapid lithium-ion transportation. The self-limited SSE thin films are evaluated in various ASS LMBs with different types of cathode (sulfur and lithium titanate) and anode materials (lithium and lithium-indium alloy) at both mold-cell and pouch-cell levels, demonstrating a stable performance and high-rate capability. This study provides a general strategy for the rational design of an SSE thin film towards high-energy-density ASS batteries.