Arumugam Manthiram

Ethers as electrolyte cosolvents in sodium-ion batteries (SIBs) provide favorable Na + solvation and interfacial properties, but their low oxidative stability limits their use in high-voltage SIBs. Herein, we address this limitation via molecular tuning of ether cosolvents for high-voltage (4.2 V) hard carbon || NaNi 0.33 Fe 0.33 Mn 0.33 O 2 full cells. Tetrahydropyran (THP) is functionalized with a nitrile group to form tetrahydropyran-4-carbonitrile (THPCN). To delineate the effect of nitrile functionalization and benchmark ether against a conventional carbonate, THP, THPCN, and diethyl carbonate (DEC) are evaluated as cosolvents with ethylene carbonate. Nitrile functionalization lowers the HOMO energy of the ether, extends the electrolyte stability window, and alters Na + solvation. Spectroscopic techniques and molecular dynamics simulations reveal that THPCN exhibits predominantly aggregate-dominated solvation (95.1%) with weakened Na + -solvent interactions, producing the most anion-rich environment relative to DEC and THP cosolvents. THPCN-modified solvation promotes the formation of highly conductive, fluorine-enriched interphases that suppress parasitic reactions. Pouch full cells with THPCN sustained ∼600 cycles at 4.2 V, outperforming THP and DEC. Operando gas analysis reveals that THPCN reduces CO 2 generation by 45% and H 2 generation by 30% relative to THP. The findings demonstrate nitrile functionalization as a molecular design strategy to stabilize ethers and enable high-voltage SIBs.

ABSTRACT Lithium‐sulfur (Li‐S) batteries are a promising next‐generation energy storage solution, as they can reduce reliance on critical transition metals while offering high energy densities. However, their deployment is hindered by low sulfur utilization and the formation/diffusion of lithium polysulfides (LiPSs). While transition‐metal catalysts and polymeric binders have been independently developed to enhance redox kinetics and LiPS adsorption, their mutual compatibility has remained largely unexplored. We show here that binder‐catalyst interactions can significantly impact catalytic performance. Employing TiO 2 as a generic catalyst, the electrochemical performance is shown to depend strongly on the binder environment. TiO 2 paired with lithiated polyacrylic acid (LiPAA) shows benign interactions, resulting in enhanced cycle life. In contrast, pairing TiO 2 with protonated PAA produces antagonistic interactions that hinder Li 2 S growth. A mechanistic analysis unveils that the carboxylic H atom in PAA promotes COO − coordination to Ti sites, occupying catalytic centers and suppressing LiPS adsorption, increasing charge transfer and diffusion resistances. This phenomenon is observed across multiple catalysts, indicating that COOH‐functionalized binders may broadly hinder catalytic activity. Overall, this study underscores the need for holistic cathode design and identifies binder‐catalyst compatibility as an important parameter for high‐performance Li‐S batteries.

ABSTRACT Lithium‐sulfur (Li‐S) batteries are a promising next‐generation energy storage solution, as they can reduce reliance on critical transition metals while offering high energy densities. However, their deployment is hindered by low sulfur utilization and the formation/diffusion of lithium polysulfides (LiPSs). While transition‐metal catalysts and polymeric binders have been independently developed to enhance redox kinetics and LiPS adsorption, their mutual compatibility has remained largely unexplored. We show here that binder‐catalyst interactions can significantly impact catalytic performance. Employing TiO 2 as a generic catalyst, the electrochemical performance is shown to depend strongly on the binder environment. TiO 2 paired with lithiated polyacrylic acid (LiPAA) shows benign interactions, resulting in enhanced cycle life. In contrast, pairing TiO 2 with protonated PAA produces antagonistic interactions that hinder Li 2 S growth. A mechanistic analysis unveils that the carboxylic H atom in PAA promotes COO − coordination to Ti sites, occupying catalytic centers and suppressing LiPS adsorption, increasing charge transfer and diffusion resistances. This phenomenon is observed across multiple catalysts, indicating that COOH‐functionalized binders may broadly hinder catalytic activity. Overall, this study underscores the need for holistic cathode design and identifies binder‐catalyst compatibility as an important parameter for high‐performance Li‐S batteries.

Abstract Lithium–sulfur (Li–S) batteries show great promise as the next‐generation rechargeable batteries, yet they still suffer from polysulfide shuttling and interphasial instability. Electrolyte, as the medium for ion transport and sulfur conversion, plays a crucial role in overcoming these challenges. Here, we introduce a moderately solvating electrolyte (MSE) based on low‐density, low‐viscosity, and nonfluorinated ether co‐solvents that balances polysulfide suppression, Li metal stabilization, and redox kinetics. Through multiple solvent–solvent and solvent‐ion interactions, the optimized MSE weakens Li + ‐solvent pairing while strengthening cation–anion interactions, thereby lowering the desolvation barrier and promoting the formation of a favorable solid–electrolyte interphase (SEI). Meanwhile, MSE limits the polysulfide dissolution but improves the accessibility of active material through better wettability and tailored solvation environment, leading to an altered sulfur deposition mechanism with β – α conversion. This approach enables a stable cycling of high‐mass loading Li–S cells (> 3.5 mg cm −2 ) at both room temperature and 45 °C (where shuttling and side reactions are severer), and demonstrates a pouch cell with lean electrolyte content (4.5 µL mg s −1 ). This work highlights a practical route to develop high‐performance electrolyte for Li–S cells and provides mechanistic insights into their operation.

Abstract Lithium–sulfur (Li–S) batteries show great promise as the next‐generation rechargeable batteries, yet they still suffer from polysulfide shuttling and interphasial instability. Electrolyte, as the medium for ion transport and sulfur conversion, plays a crucial role in overcoming these challenges. Here, we introduce a moderately solvating electrolyte (MSE) based on low‐density, low‐viscosity, and nonfluorinated ether co‐solvents that balances polysulfide suppression, Li metal stabilization, and redox kinetics. Through multiple solvent–solvent and solvent‐ion interactions, the optimized MSE weakens Li + ‐solvent pairing while strengthening cation–anion interactions, thereby lowering the desolvation barrier and promoting the formation of a favorable solid–electrolyte interphase (SEI). Meanwhile, MSE limits the polysulfide dissolution but improves the accessibility of active material through better wettability and tailored solvation environment, leading to an altered sulfur deposition mechanism with β – α conversion. This approach enables a stable cycling of high‐mass loading Li–S cells (> 3.5 mg cm −2 ) at both room temperature and 45 °C (where shuttling and side reactions are severer), and demonstrates a pouch cell with lean electrolyte content (4.5 µL mg s −1 ). This work highlights a practical route to develop high‐performance electrolyte for Li–S cells and provides mechanistic insights into their operation.

High-voltage cycling is critical for high cathode-level energy density in sodium solid-state batteries. We present interactions between NaAlCl 4 catholytes and oxide cathodes and investigate fluorination strategies to enhance high-voltage stability.

Lithium-ion batteries operate well between a temperature range of 15 °C to 35 °C. However, sluggish kinetics due to the resistive solid-electrolyte interphase (SEI) layer can impede the charge-transfer process below this range, and above this range, accelerated decomposition of the electrolyte on the surface of the electrodes leads to continuous growth of high-impedance SEI and cathode-electrolyte interphase (CEI) films. In traditional nonaqueous electrolytes, a Li + salt is dissociated in the presence of a strongly coordinating solvent like ethylene carbonate (EC), while a comparatively weaker coordinating solvent, for example, ethyl methyl carbonate (EMC), is employed to transfer the solvated Li + through the bulk electrolyte between the electrodes. In electrolyte design, the selection of Li + salt and solvents are fundamental to controlling the composition of SEI and CEI films, and thus the performance of the battery over a wide-temperature range. This presentation will focus on identifying the resultant interactions between the Li + salt counter ion and the electrolyte cosolvents across a wide-temperature range of -40 °C to 60 °C. Specifically, we selected LiPF 6 , LiDFOB, and LiFSI to be tested with varied ratios of EC and EMC to identify the best combination for the improved cycling performance of Li 1.02 Ni 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode and graphite anode full cells. Current literature asserts that EC assists in LiPF 6 electrolytes due to the benefits of a higher dielectric constant and by formation of an SEI with greater high-temperature stability and conductivity than those formed by EMC. This work demonstrates the opposite effect in LiDFOB electrolytes, where EC-free electrolytes deliver improved -40 °C discharge performance and higher stability during 60 °C cycling. We identify the ways in which dual-salt systems can be employed to amalgamate the benefits of each Li + salt, culminating in a tailored electrolyte design for wide-temperature cycling of lithium-ion batteries. In this work, electrochemical impedance spectroscopy (EIS) analysis indicates that electrolytes with EC > 20 v% exhibit impedance growth in the charge-transfer resistance (R ct ) of the cell, regardless of the choice of Li + salt. Furthermore, electrolytes with EC < 20 v% experience more growth in the high-frequency region associated with contact resistance (R contact ). Impedance measurements collected at -40 °C identify LiDFOB as generating the lowest cell impedance in EMC, while the smallest amount of impedance growth after high temperature cycling occurs for a dual-salt combination of 0.5 M LiDFOB + 0.5 M LiFSI in EMC. The highest -40 °C discharge capacity retention for single-salt electrolytes is achieved by 1 M LiDFOB in EMC, followed closely by 1 M LiPF 6 in EMC and 0.5 M LiPF 6 + 0.5 M LiFSI. These findings give rise to an improved understanding of the interactions of common nonaqueous electrolyte co-solvents with different Li + salts. By identifying Li + salt and solvent combinations favorable for wide-temperature performance, we suggest new electrolyte formulas designed to assist in extending the temperatures lithium-ion batteries can reliably operate within. ACKNOWLEDGEMENT This work was supported by a NASA Space Technology Graduate Research Opportunity. Some of the work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). The information in this document is pre-decisional and is provided for planning and discussion only.

Energy storage has become an integral part of our daily life with portable electronic devices and electric vehicles. Lithium-ion batteries currently dominate the market due to their high operating voltage and energy density. However, as the battery market is booming, cost, sustainability, and supply-chain issues will be the dominant challenge. In this regard, batteries with sulfur as a cathode, instead of the currently used transition-metal oxide and polyanion oxide cathodes, are appealing as sulfur is abundant, environmentally benign, and store an order of magnitude higher charge than the transition-metal oxide cathodes. Moreover, sulfur is a byproduct in the petrochemical industry, so successful development of sulfur-based batteries will offer an opportunity to utilize the waste sulfur-based byproducts as a value-added commodity. Furthermore, use of sodium as working ion instead of lithium will make sodium-sulfur batteries as a mined-metal-free battery system as sodium is plenty in the ocean. Unfortunately, sulfur-based batteries are hampered by severe fundamental and technological challenges. First, sulfur is a poor electronic and ionic conductor, necessitating the addition of significant amount of carbon and electrolyte into the cell, which drastically lowers the practical energy density and makes sulfur-based batteries uncompetitive. Second, the intermediate discharge products, viz., polysulfides, dissolve in the liquid electrolyte, crossover from the cathode to the anode, and shuttle back and forth between the cathode and anode during the charge-discharge process. The polysulfide shuttle reduces the efficiency, degrade the metal anodes, and diminish the cycle life. To overcome the persistent challenges, this presentation will center on the design and development of new liquid electrolytes for both lithium-sulfur and sodium-sulfur batteries as well as on all-solid-state lithium-sulfur and sodium-sulfur batteries. Use of a solid-electrolyte instead of liquid electrolytes can eliminate the dissolution and shuttling of polysulfides. With liquid electrolytes, the presentation will focus on delineating the intricacies associated with the solvation structure and interfaces, employing advanced characterization methodologies, such as in-situ X-ray diffraction, X-ray photoelectron spectroscopy, time-of-flight – secondary ion mass spectrometry, nuclear magnetic resonance spectroscopy, etc. With all solid-state lithium-sulfur and sodium-sulfur batteries, the presentation will bring out the complexities involved in incorporating the solid electrolyte and carbon into sulfur cathode.

Solid-state Na-ion batteries are an attractive format due to their potential lower cost compared to Li-based systems and higher energy density compared to liquid electrolyte Na-ion systems. To achieve these potential benefits, energy-dense layered-oxides are the typical cathode active material of choice. However, Na-based solid electrolytes must exhibit sufficient oxidative stability (~ 4 V vs. Na/Na + ) and chemical compatibility to be paired with layered-oxide cathodes. Halide solid electrolytes have gained significant interest recently as catholytes because they fit these criteria. However, most halides with sufficient electrochemical properties utilize rare and/or expensive metals such as Y, Er, Zr, Nb, Ta, and La, which undermines the cost benefits of Na-based batteries. NaAlCl 4 is a promising electrolyte due to its basis on low-cost, extremely abundant aluminum and its oxidative stability to ~ 4 V vs. Na/Na + , but it suffers from low ionic conductivity. This presentation focuses on effective strategies to tailor the anion chemistry of NaAlCl 4 -based solid electrolytes to enhance key electrochemical properties: ionic conductivity and oxidative stability. Introduction of O 2- anions result in a drastic boost in ionic conductivity by 2-3 orders of magnitude, depending on the oxide precursor and synthesis method employed, due to the formation of highly amorphous, mixed phase oxychlorides. Additionally, preliminary F - anion incorporation results suggest that mixed aluminum-halide complexes can effectively extend the oxidative decomposition voltage of the solid electrolyte beyond 4 V vs. Na/Na + , likely due to the formation of passivating, F-rich decomposition products. This improved stability is also accompanied by a moderate increase in ionic conductivity. An expanded oxidative stability limit can support higher voltage cutoff cycling in all-solid-state batteries, achieving higher cathode-level capacity and energy density. Spectroscopic techniques, such as solid-state magic angle spinning NMR, prove to be invaluable for elucidating the complex, mixed-anion local structure of the resultant solid electrolytes and provide insights into the origin of the improved electrochemical properties. These results showcase the ongoing work in our lab to develop high-performing, next-generation battery materials, while maintaining an outlook toward sustainability and practical material costs.

Lithium-ion batteries have aided our modern lifestyle with portable electronic devices and electric vehicles. The success of lithium-ion batteries became possible because of the use of transition-metal oxide cathodes with high operating voltages and energy density. The fundamental solid-state inorganic chemistry embarked in the 1980s led to the discovery and development of oxide cathodes. They are layered, spinel, and polyanion oxide cathodes. Among them, the layered and polyanion oxide cathodes dominate the commercial lithium-ion battery market for portable electronics and electric vehicles. They are also now intensively pursued for grid storage of electricity. In order for a battery technology to be successful, cost, energy density, power density, cycle life, safety, and environmental impact need to be considered and balanced. In lithium-ion batteries, cathodes are the most expensive. They also impact the cell energy density and safety. As the battery market is expanding rapidly, cost along with supply chain issues will be the dominant factor. The oxide cathodes will still dominate the field, but with fierce efforts to reduce or eliminate less abundant and expensive metals in the cathode. After a brief overview of the historical development of oxide and polyanion oxide cathodes over the past four decades, this presentation will focus on eliminating or reducing the most expensive cobalt, then the next expensive nickel, and finally eliminating lithium itself with sodium in layered or polyanion oxide cathodes. The presentation will articulate the fundamental, intricate roles of electronic configuration, crystal structure, chemical bonding (ionic vs. covalent), and chemical reactivity on the electrochemistry of oxide and polyanion oxide cathodes for both lithium-ion and sodium-ion batteries. With a goal of reducing cost and enhancing durability, blend cathodes consisting of a layered oxide and a polyanion oxide without compromising the energy density too much will also be discussed. Particular attention will be paid towards overcoming the challenges with controlled compositional designs of cathodes and electrolytes along with a profound understanding of the complexities involved with the aid of advanced characterization methodologies. Finally, moving forward, how the power of artificial intelligence (AI) could aid accelerated discovery of new materials and battery chemistries will be commented.

LiMn x Fe 1−x PO 4 (LMFP) cathodes can improve the energy density of lithium-ion batteries by up to 15% compared to LiFePO 4 due to the higher operating voltage of the Mn 2+/3+ redox couple (4.0 V vs. Li/Li + ) compared to that of Fe 2+/3+ (3.4 V vs. Li/Li + ). However, the sluggish kinetics of the Mn 2+/3+ redox couple, caused by Jahn-Teller active Mn 3+ , have been a challenge for the commercial viability of LMFP cathodes. To address these kinetic problems, active material modification is commonly pursued. Doping inactive ions and reducing the particle size to overcome the kinetic issues with LMFP, thereby achieving its full theoretical capacity, consequentially limit the energy density severely. Overall, there is a complex tradeoff between Mn 2+/3+ redox reaction kinetics and electrode density, which both have a role in dictating the practical energy density of LMFP cathodes. This presentation will focus on an investigation of the fundamental behaviors and possible solutions to both sides of this tradeoff. To improve the electrode density of LMFP, a low-cost synthesis of dense LMFP cathode material has been developed by employing a spinel LiMnFeO 4 precursor obtained by a facile solid-state reaction. While LMFP synthesized with the spinel precursor offers a lower specific capacity than commercial LMFP, it exhibits a ∼ 15% higher electrode-level energy density due to its exceptional electrode compression density (2.6 g cm −3 ). To understand the kinetic limitations of the Mn 2+/3+ redox couple, various kinetic testing procedures have been conducted on LMFP cathodes to expose the conditions that exacerbate the impacts of Jahn-Teller distortion and diminish the electrochemical performance of the cathode. Operando electrochemical impedance spectroscopy reveals the resistance trends throughout this redox reaction. Mn-content, temperature, and charging rate all impact the resistance, and therefore the degree of utilization of the Mn 2+/3+ redox couple. An in-depth understanding of the influence of these parameters on the Mn 2+/3+ redox couple can offer valuable insights for further optimizing the composition and synthesis conditions of LMFP and enhancing its commercial viability.

The development of next-generation energy storage technologies is crucial as the world shifts to renewable energy sources to address the climate crisis. While Li-ion batteries are mature and commercially successful, their energy density and costs are insufficient for future energy requirements. Lithium-sulfur (Li-S) batteries are a promising candidate due to their high theoretical energy density and the abundance of sulfur—an inexpensive and environmentally friendly substitute for the mined precious metals in conventional batteries. However, to achieve high energy densities, high sulfur loadings and minimized electrolyte-to-sulfur ratios are required. Such practical conditions often lead to low capacities and poor cycle life due to sluggish sulfur kinetics and accelerated electrode degradation. This presentation focuses on how these challenges can be mitigated by optimizing the cathode microstructure. A scalable spray-drying process is employed to tailor the particle morphology of a sulfur/carbon composite, resulting in a cathode with uniform sulfur distribution and enhanced mechanical stability. Under stringent parameters, these electrodes deliver high capacities and improve the cycle life of a Li-S cell. The cell overpotential is further deconvoluted to identify key factors restricting faster rate performance. The typical kinetic barriers (activation polarization) are significantly alleviated at the potential-limiting Li 2 S nucleation step. Although diffusion limitations (concentration polarization) are also reduced, it emerges as the dominant contributor to the cell overpotential. Catalyst design alone can only mitigate the activation polarization, underscoring the need for continued optimization of the electrode microstructure to further reduce the concentration polarization. In all, this study highlights the critical role of electrode architecture design in advancing Li-S batteries toward commercial viability.

Abstract Sodium‐ion batteries (SIBs) are attractive for the low cost and abundance of sodium. Yet, gas evolution—a critical challenge in SIBs—remains underexplored. Here, online electrochemical mass spectrometry is used to probe gas evolution in layered oxide cathodes with various compositions, cutoff voltages, dopants, and particle morphologies. Compared to LiNiO 2 (LNO), NaNiO 2 releases more gas, even at lower states of charge, due to the higher covalency of Ni─O bond caused by the more ionic Na─O bond through the inductive effect. Among Co, Mn, Al, and Mg, Mn and Mg doping suppress gas release most effectively by enhancing the metal‐oxygen bond strength. NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathodes synthesized via coprecipitation (CP‐NFM) and solid‐state routes exhibit distinct particle morphologies; CP‐NFM exhibits more gas evolution, yet secondary particle morphology helps reduce it through differential cathode‐electrolyte reactivity between inner and outer primary particles. Among Li, Ti, Mg, and Cu doping in NFM, Li has the largest effect, reducing gas levels comparable to LNO. Nuclear magnetic resonance and X‐ray photoelectron spectroscopies reveal that electrolyte solvent decomposition mainly produces organic‐rich cathode‐electrolyte interphase (CEI) rather than soluble species. NaPF 6 salt further exacerbates cathode‐electrolyte reactions, forming surface Na 2 O species. The findings provide actionable guidance for designing safer, durable SIBs.

All-solid-state lithium-sulfur batteries are a promising platform due to their high gravimetric energy density and enhanced safety. However, they face numerous challenges that currently obstruct commercial adoption. The key to overcoming these challenges lies in the rational selection and targeted development of solid-state electrolytes, where different materials classes present distinct trade-offs between performance and practicality. We assert that sulfide electrolytes offer the best compatibility with the cathode and anode requirements for practical sulfur cells, with halides and borohydrides also showing potential for use in the cathode with further development. We provide cell-level target parameters to ensure that the field moves consistently towards commercial relevance. Looking forward, we call for the adoption of the chlorinated argyrodite with a composition range of Li6-xPS5-xCl1+x (x = 0 − 0.5) as a standardized solid-state electrolyte to enable rigorous benchmarking across the field and accelerate battery development. Solid-state electrolytes are key to the successful implementation of high-performance all-solid-state lithium-sulfur batteries. This Review discusses the different classes of materials that can be used for electrolytes, focusing on sulfides, halides, oxides, and borohydrides.

Abstract All‐solid‐state batteries (ASSBs) are critical for achieving high energy density and enhanced safety. Solid polymer electrolytes (SPEs) offer key advantages over other electrolytes, including improved safety, flexibility, and interfacial contact. Among the SPEs, ether‐based polymers are widely studied due to their ease of processing and high ionic conductivity (σ i ) in the amorphous state. In this work, the introduction of poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) into an SPE matrix composed of poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) (PEG2k), and sodium bis(fluorosulfonyl)imide (NaFSI) salt is investigated to facilitate the formation of amorphous, high σ i SPEs through end‐group engineering and polymer ratio optimization. PEGMEMA enhances structural integrity via crosslinking with PEGDA through its methacrylate group, while its methyl end group aids ion conduction. A 2:1:7 ratio of PEGDA:PEGMEMA:PEG2k exhibits a σ i of 1.16 x 10 −4 S cm −1 and oxidative stability up to 4.4 V at 60 °C. A solid‐state cell incorporating this SPE, a Na 2/3 Ni 1/3 Mn 2/3 O 2 (NM12) cathode, and a sodium‐metal anode demonstrates excellent cycling stability, retaining over 80 % of its initial capacity for 150 cycles at 60 °C. The findings highlight the potential of end‐group engineering in improving the electrochemical performance of SPEs.

High-nickel (Ni) (≥80%) single-crystal LiNi 1- x - y Mn x Co y O 2 (NMCs) have garnered recent interest as cathodes in lithium (Li)-ion batteries (LIBs). However, capacity fade at high voltages, particularly after the onset of the H2–H3 phase transition, hampers their viability. In this study, single-crystal LiNi 0.8 Mn x Co 0.2- x O 2 ( x = 0.2, 0.1, 0) are synthesized and tested in LiPF 6 in ethyl methyl carbonate-based electrolytes, with and without monofluoroethylene carbonate and LiF 2 PO 2 additives, to clarify the effects of Co/Mn ratio and surface stabilization on high-voltage cycling degradation. By imposing a kinetic barrier to the accessible H2–H3 capacity, surface reconstruction is identified as the primary driver of high-voltage capacity loss, being greater in the Co-free cathode and in the absence of fluorinated electrolyte components. This is attributed to a synergy between increased mechanical stress due to worsened bulk and interfacial H2–H3 kinetics and decreased interfacial stability due to the poor passivating capability of the electrolyte. The findings highlight the importance of limiting cathode impedance growth during high-voltage cycling, which can be achieved by tuning bulk dopants and electrolyte chemistry.

Sodium-sulfur (Na-S) batteries have attracted considerable attention due to their high theoretical energy density and the abundant natural availability of sodium and sulfur. However, sluggish kinetics of sulfur conversion, slow Na⁺ transport, and interfacial instability at low temperatures pose significant challenges for their operation and limit their practical application. Herein, three solvents with well-designed molecular configurations are examined. We systematically investigate the impact of chelation effect on the desolvation behavior, sulfur conversion process, ion dynamics, and Na⁺ plating/stripping behavior. Compared with conventional linear ether solvents, the incorporation of methyl groups not only weaken the chelation capability and tailors the inner solvation sheath, but also reduces the energy barrier for Na⁺ transport, thus promoting enhanced sulfur conversion kinetics under low temperature conditions. This work elucidates the relationship among solvent molecules, Na⁺ desolvation behavior, and sulfur reaction kinetics, and offers a strategy for rational design of electrolytes for low-temperature metal-sulfur batteries.

Abstract Sodium–sulfur (Na–S) batteries have attracted considerable attention due to their high theoretical energy density and the abundant natural availability of sodium and sulfur. However, sluggish kinetics of sulfur conversion, slow Na⁺ transport, and interfacial instability at low temperatures pose significant challenges for their operation and limit their practical application. Herein, three solvents with well‐designed molecular configurations are examined. We systematically investigate the impact of chelation effect on the desolvation behavior, sulfur conversion process, ion dynamics, and Na⁺ plating/stripping behavior. Compared with conventional linear ether solvents, the incorporation of methyl groups not only weaken the chelation capability and tailors the inner solvation sheath, but also reduces the energy barrier for Na⁺ transport, thus promoting enhanced sulfur conversion kinetics under low temperature conditions. This work elucidates the relationship among solvent molecules, Na⁺ desolvation behavior, and sulfur reaction kinetics, and offers a strategy for rational design of electrolytes for low‐temperature metal–sulfur batteries.

Abstract As the push for lithium‐ion batteries (LIBs) with high‐energy density grows, systems pairing high‐nickel cathodes with high‐capacity anodes have become attractive; however, these electrodes individually suffer from high surface reactivities, leading to interfacial instabilities. When paired together, further issues arise, with cathode‐to‐anode crossover being a well‐known phenomenon. In contrast, anode‐to‐cathode crossover remains underexplored, especially in systems that undergo large volume changes. Here, a comparison of the influence of anode reactivity on cathode surface degradation is presented by pairing LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode with graphite, prelithiated silicon suboxide (SiO x ), and lithium‐metal anodes. Voltage curves and differential capacity analysis show that all cells experience polarization growth throughout cycling. A combination of electrochemical techniques, such as operando galvanostatic electrochemical impedance spectroscopy (GEIS), and surface analyses, such as scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS), reveal that cycling against more reactive anodes promotes the formation of a thicker, organic‐rich cathode electrolyte interphase (CEI), which suffers from impedance growth and large irreversible capacity loss. Post‐mortem characterization with XPS and SEM confirms compositional and morphological changes at the cathode surface and the cycled separator. The findings provide insights into the role of anode‐driven degradation of high‐Ni cathodes, promoting further understanding of two‐way crossover in LIBs.

Abstract Unwanted cathode‐electrolyte side reactions remain a major challenge to the stability of lithium‐ion batteries, especially at high temperatures. This study presents a quantitative analysis on gaseous, soluble, and solid byproducts generated by reactions between LiNiO 2 and carbonate electrolytes. Online electrochemical mass spectrometry (OEMS) outgassing profiles reveal the emergence of a pre‐plateau region as temperature increases, characterized by two small plateaus at 3.7 and 4.0 V, which are attributed to catalytic ethyl methyl carbonate (EMC) decomposition and ethylene carbonate (EC) hydrolysis, respectively. Activation energies for electrolyte oxidation reactions are quantified with OEMS, confirming that the main outgassing event is driven by direct oxygen‐electrolyte chemical reactions. Nuclear magnetic resonance and X‐ray photoelectron spectroscopy analyses show that EC decomposition yields both soluble and solid byproducts, while EMC produces mainly solid species, leading to a thicker, organic‐rich cathode‐electrolyte interphase; the presence of LiPF 6 further accelerates solvent degradation. Additionally, the effectiveness of various dopants in suppressing gas evolution is evaluated across a broad temperature range, with magnesium‐doped cathodes exhibiting the most effective suppression by stabilizing lattice oxygen. Overall, this work establishes a clear correlation among triphasic side‐reaction products, guiding rational design of cathode materials and electrolyte formulations for high‐energy lithium‐ion batteries.

Abstract All‐solid‐state lithium‐sulfur batteries (ASSLSBs) offer enhanced safety, energy density, and cost efficiency. However, the insulating nature of sulfur necessitates excessive conductive carbon to support sulfur redox. Common sulfide solid‐state electrolytes (SSEs) like Li 5.5 PS 4.5 Cl 1.5 decompose electrochemically within the operating voltage range of sulfur, a process enhanced by intimate contact with carbon. While this decomposition increases cell capacity, it reduces ionic conductivity, and its link to carbon characteristics in sulfur cathodes remains underexplored. Herein, the relationship between carbon specific surface area (SSA) and SSE decomposition in sulfur cathodes is examined. It is established that carbon blending can form a robust electronic conducting network that enhances both SSE and sulfur redox independently of carbon SSA. With a second derivative analysis (SDA), electrochemical impedance spectroscopy (EIS), and a galvanostatic intermittent titration technique (GITT), sulfur redox is separated from SSE redox, and active material loss is established as the dominant failure mechanism. Carbon blending with nanofibers is shown to mitigate cell fading despite increasing SSE decomposition. Finally, optimized cathodes are synthesized with high SSE and sulfur capacity capable of high‐rate cycling and cycling at high S‐loading against Li‐metal. The study highlights how tailoring carbon blends can significantly improve sulfur utilization, cyclability, and rate performance in ASSLSBs.

The deposition of metallic lithium inside inorganic solid-state electrolytes (SSEs) is a challenge that poses a concern for the development of all-solid-state lithium batteries. Unlike lithium dendrites that form and grow from the surface of Li-metal anode, metallic lithium can nucleate and propagate directly inside the bulk SSE, which can cause an instant failure of SSE. This aim of this Review was to provide a timely report on the progress of relevant research from both theoretical and experimental aspects. We first discuss the formation mechanism of metallic lithium inside SSEs from thermodynamic, kinetic, and electrochemical points of view. Then, recent research efforts toward a direct observation of metallic Li inside SSEs are summarized. Mechanisms proposed regarding intergranular and intragranular deposition of Li, direct nucleation of Li inside SSEs driven by the electronic conductivity of SSE, and reduction of Li caused by excess electrons or negatively charged species are discussed in detail. On the basis of theoretical and experimental discussions, we propose future research directions. With this Review, we hope to stimulate the researchers in the field of all-solid-state batteries toward a deep understanding of the Li deposition behavior inside SSEs and formulating proper strategies to address the issue.

Sodium–sulfur batteries promise high-energy-density and sustainable electrochemical energy storage but suffer from uncontrolled polysulfide dissolution and high sodium reactivity. These challenges fundamentally originate from poor electrolyte–electrode compatibility. Current electrolyte research inadequately addresses the trade-off between minimal polysulfide solvation and stabilizing sodium interfaces. Here, we present a locally confined polysulfide-reactive electrolyte strategy that mediates the polysulfide dissolution dynamics and sodium stability by leveraging an electrophilic solvating species with a localized high-concentration electrolyte. This design enables shuttle-free cell operation by synergistically restricting the global solvating power of the electrolyte through intermolecular interactions and locally scavenging sparingly dissolved polysulfides via electrolyte electrophilicity. The precisely confined surface reaction facilitates a protective cathode–electrolyte interface, realizing a quasi-solid-state sulfur conversion in our liquid ether-based electrolyte, which crucially avoids crossover-induced catastrophic sodium–metal degradation. The proposed electrolyte demonstrates long-term cycling of high-mass-loading sulfur cathodes (>3 mg S cm –2 with commercial carbon host and 70 wt % sulfur content), which afford 710 mA h g –1 over 400 cycles in coin cells and steady pouch cell operation over 180 cycles. This work establishes a scalable electrolyte design protocol that regulates the reaction chemistry of highly reactive electrodes, offering a pathway toward sustainable renewable energy storage.

Lithium (Li)-metal batteries with high-voltage cathodes are promising next-generation, high-energy automotive batteries. While ether-based electrolytes are known for their high reductive stability, their limited oxidative stability against high-voltage cathodes remains a key barrier to long-term service life. Here, we present a methodology enabling a comprehensive, quantitative assessment of cathode–electrolyte reactions, based on a model fluorinated 1,2-diethoxyethane-based electrolyte and LiNiO 2 cathode. Online electrochemical mass spectroscopy at varying temperatures reveals both the thermodynamic and kinetic features of the electrolyte oxidative decomposition by quantifying gaseous byproducts and the reaction activation energy. Nuclear magnetic resonance spectroscopic results unveil alcohol and alkoxy acetic acid species as soluble decomposition products of ether electrolytes. Time-of-flight secondary ion mass spectrometry, combined with region-of-interest and spatial normalized standard deviation analyses, quantitatively determines the thickness and spatial and chemical homogeneity of the cathode–electrolyte interphase. This work establishes a quantitative methodology to assess gaseous, soluble, and solid cathode–electrolyte decomposition products.

Abstract Lithium‐ion batteries (LIBs) operate without significant degradation between a temperature range of +15 and +35 °C. In the design of electrolytes, the selection of Li + salt and solvents determine the composition of solid‐electrolyte interphase (SEI) and cathode‐electrolyte interphase (CEI) films. This work identifies the resultant interactions of Li + salt anions and electrolyte cosolvents across a wide‐temperature range of −40 to +60 °C. Specifically, this work selects lithium hexafluorophosphate (LiPF 6 ), lithium difluoro(oxolato)borate (LiDFOB), and lithium bis(fluorosulfonyl)imide (LiFSI) for testing in varied ethylene carbonate (EC) and ethyl methyl carbonate (EMC) ratios in Li 1.02 Ni 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode and graphite anode full cells. Electrochemical impedance spectroscopy (EIS) analysis indicates that electrolytes with EC > 20 v% exhibit charge‐transfer resistance (R ct ) growth, while electrolytes with EC < 20 v% experience larger growth in the high‐frequency region associated with SEI and CEI resistance. Symmetric cells of electrodes cycled in single‐salt EC‐free electrolytes indicate that high impedance growth occurs on the cathode in LiPF 6 electrolytes and the anode in LiFSI electrolytes, while LiDFOB passivates both electrodes, improving the retention of low‐temperature performance after high‐temperature cycling. By identifying Li + salt and solvent combinations favorable for wide‐temperature performance, this work suggests new electrolyte formulas designed to assist in extending the temperature range LIBs can reliably operate.

Abstract Alkali metal‐sulfur batteries, including lithium‐sulfur (Li‐S), sodium‐sulfur (Na‐S), and potassium‐sulfur (K‐S) systems, have garnered significant attention as promising electrochemical energy storage (EES) technologies. Among them, Li‐S batteries stand out as strong contenders for next‐generation energy storage, owing to their high energy density and the cost‐effectiveness of sulfur‐based cathodes. However, with the rapid technological advances and the escalating energy demand, lithium resources are becoming increasingly scarce, making it imperative to explore alternative metal anodes to replace lithium. Therefore, Na‐S and K‐S batteries, serving as counterparts to Li‐S systems, are emerging as formidable contenders for next‐generation energy storage technologies due to the abundant and cost‐effective nature of sodium and potassium. Although Na‐S and K‐S batteries possess considerable potential in the energy sector, their development is still in its infancy, with performance constrained by the nascent state of electrolyte design and optimization. This review article provides a comprehensive overview of recent advancements and developments in liquid electrolytes for alkali metal‐sulfur batteries. Additionally, it identifies key challenges and proposes future research directions aimed at enhancing electrolyte stability, optimizing interfacial compatibility, and improving the overall performance of alkali metal‐sulfur batteries.

Abstract Lithium–sulfur (Li–S) batteries offer high theoretical energy density and employ earth‐abundant sulfur, making them a promising next‐generation energy storage technology. Although essential for practical energy densities, high sulfur loadings, and lean‐electrolyte contents lead to poor sulfur kinetics/utilization and cycle life. This study highlights the critical role of electrode microstructure in resolving these challenges. The particle morphology and size of a ketjenblack/sulfur composite are controlled through a scalable spray‐drying procedure (SD‐KB/S), producing an optimized cathode structure with uniform sulfur distribution and enhanced mechanical integrity with minimal electrode cracking. At a sulfur loading of 4 mg cm −2 and an electrolyte‐to‐sulfur (E/S) ratio of 6, SD‐KB/S cathodes exhibit stable cycling performance, retaining a capacity of 768 mA h g −1 after 100 cycles, contrasting severe capacity fade with conventional electrodes. A cell overpotential deconvolution unveils that the activation overpotential (typically the largest barrier in conventional cells) is notably reduced in SD‐KB/S cells. Although the concentration overpotential is also reduced with SD‐KB/S, it becomes a prominent contributor to cell polarization, revealing the need to consider diffusional limitations in practical Li–S batteries. This work emphasizes the importance of advancing electrode and catalyst design concurrently—rather than sole catalyst development—to achieve high‐performance and commercially viable Li–S batteries.

Abstract The electrochemical urea oxidation reaction (UOR) is substantiated as a promising pathway for transforming waste into renewable power. Hollow ball‐like architectures composed of 3D carbon shell‐encased Ni–Cu nanoparticles in multi‐walled carbon nanotubes (Ni x ‐Cu y /MWCNTs) have been synthesized, utilizing a bimetallic organic framework as a soft template in conjunction with chemical vapor deposition. The configurational and electronic traits of the as‐formulated catalysts and their impact on charge‐transfer processes are elucidated with density functional theory, and their influence on UOR kinetics is then explicated with various electrochemical techniques. The hierarchical porous hollow spherical bundles of Ni x ‐Cu y /MWCNTs accelerate urea utilization efficacy, as their interior and exterior surfaces are exposed to urea fuel. The synergistic interaction between bimetallic nanoparticles and graphitic carbon helps enhance the electron conduction pathways, electrocatalytic activity, and anti‐poisoning ability toward UOR. Compared to commercial Ni/C, the Ni x ‐Cu y /MWCNTs catalyst enables direct urea fuel cells (DUFC) with a high‐power density (47.3 mW cm −2 ) and longevity (200 h), benefiting from the energetically favored oxidation of UOR intermediates and suppressed N─C bond cleavage facilitated by the surface and interstitial vacancies in Ni x ‐Cu y /MWCNTs. Moreover, 32.7 mW cm −2 along with resilience against human urine fuel is achieved in DUFC, opening up research endeavors in sustainable energy development.

Abstract The stability of the solid–electrolyte interphase (SEI) is critical to the cycle life of lithium‐metal batteries (LMBs). While the crossover effect of transition‐metal ions from cathode to anode is extensively studied in lithium‐ion batteries with graphite anodes, its impact on LMBs remains largely unexplored. Herein, this study investigates the electrochemical and chemical properties of SEI layers formed on lithium‐metal anodes in localized high‐concentration electrolytes (LHCEs) containing dissolved transition‐metal ions (Ni 2+ , Mn 2+ , and Co 2+ ). It is demonstrated that transition‐metal ions in LHCEs reduce the coulombic efficiency (CE) and significantly degrade the cycle life of LMBs. Time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS) reveals that SEI structures differ depending on the dissolved TM ion, with Mn 2+ and Co 2+ inducing severe destabilization, and Ni 2+ exhibiting a less severe impact. These findings underscore the detrimental effects of transition‐metal crossover effects in LMB systems.

Room-temperature sodium–sulfur (RT Na–S) batteries are garnering interest owing to their high theoretical energy density and low cost. However, the notorious shuttle behavior of sodium polysulfides (NaPS) and uncontrollable dendrite growth lead to the poor cycle stability of RT Na–S cells. In this work, we report the use of 1,2-dimethoxypropane (DMP) and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE) as inner solvent and outer diluent, respectively, in a localized high-concentration electrolyte system. Impressively, the asymmetric DMP as the inner solvent, introduced to replace the conventional solvent 1,2-dimethoxyethane (DME), shields NaPS effectively from incorporation into the inner solvation structure due to the extra methyl groups in the molecular structure. Furthermore, the TFTFE diluent, which contains electron-withdrawing perfluoro segments (−CF 3 – and −CF 2 −), exhibits significantly low solvation power. Consequently, the outer sheath TFTFE diluent further minimizes NaPS dissolution, thereby enhancing the cycle stability. This inner–outer sheath synergistic effect leads to the formation of highly effective cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) layers simultaneously, significantly alleviating the shuttle effect and reducing the side reactions between NaPS and sodium metal. Remarkably, the Na–S cells with the designed electrolyte present long-cycling reversibility with 530 mAh g –1 over 600 cycles at a C/2 rate and a low capacity decay rate of 0.077% per cycle. This study provides a profound understanding of the electrolyte structure involving NaPS and offers a firm basis for the rational design of electrolytes for rechargeable metal–sulfur battery systems.

Abstract Lithium argyrodite electrolytes with halide dopings (Li 6 PS 5 X, X = Cl, Br, I) are a group of sulfide solid electrolyte materials (SSEs) widely adopted in all‐solid‐state lithium–sulfur batteries (ASSLSBs) for their ease of processing and low material costs. Specifically, the Cl‐doped lithium argyrodite electrolytes, with the highest ionic conductivities among the halide‐doped lithium argyrodite electrolytes, are extensively studied in the literature. However, their narrow electrochemical stability window limits the performance of ASSLSBs due to the inevitable electrolyte decomposition within the operating voltage window. Here, the Br‐doped lithium argyrodite electrolyte (Li 5.5 PS 4.5 Br 1.5 ) is utilized as a comparison to the widely‐adopted Cl‐doped lithium argyrodite electrolyte (Li 5.5 PS 4.5 Cl 1.5 ) in ASSLSBs. Despite its slightly lower ionic conductivity, Li 5.5 PS 4.5 Br 1.5 significantly enhances the overall cell performance and cyclability of the LiIn ǁ SSE ǁ S‐C‐SSE cell due to a wider electrochemical stability window. With a better electrochemical stability of Li 5.5 PS 4.5 Br 1.5 within the working voltage range of ASSLSBs, the LiIn ǁ SSE ǁ S‐C‐SSE cell with Li 5.5 PS 4.5 Br 1.5 attains an excellent capacity retention of 90% over 100 cycles at 1.4–3.1 V and 68% over 250 cycles even at a wider voltage window of 1.1–3.1 V.

Abstract Sodium‐ion batteries (SIBs) are emerging as a viable alternative for sustainable and cost‐effective energy storage, yet their energy density is curtailed by relatively low voltage outputs (< 4 V) due to the lack of high‐voltage electrolytes. Here, for the first time, we describe a high‐voltage Na + electrolyte featuring a macromolecule‐enriched solvation architecture. The vulnerable small molecules in the Na + solvation shell are replaced by macro polyamide (PA) molecules with high thermodynamic resilience, ensuring a wide electrochemical stability window for the electrolytes with suppressed oxidative/reductive decomposition. Concomitantly, the anions engage in H‐bonding with the amido groups of PA, which not only stabilizes the anions against hydrolysis, but also delivers a high Na + transference number of 0.93. Importantly, the nitrogen‐rich composition of the macromolecule‐enriched electrolyte (MEE) fosters the formation of robust nitride interphases that impart enduring stability to both the cathode and anode. As a result, the hard carbon (HC) || NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) full cells demonstrate significant rechargeability even with an ultrahigh cutoff voltage of 4.4 V. Our approach distinctively avoids the use of fluorinated molecules typically found in (localized‐) high‐concentration electrolytes, presenting a novel principle that could revolutionize high‐voltage electrolyte design.

Abstract Sodium‐ion batteries (SIBs) are emerging as a viable alternative for sustainable and cost‐effective energy storage, yet their energy density is curtailed by relatively low voltage outputs (< 4 V) due to the lack of high‐voltage electrolytes. Here, for the first time, we describe a high‐voltage Na + electrolyte featuring a macromolecule‐enriched solvation architecture. The vulnerable small molecules in the Na + solvation shell are replaced by macro polyamide (PA) molecules with high thermodynamic resilience, ensuring a wide electrochemical stability window for the electrolytes with suppressed oxidative/reductive decomposition. Concomitantly, the anions engage in H‐bonding with the amido groups of PA, which not only stabilizes the anions against hydrolysis, but also delivers a high Na + transference number of 0.93. Importantly, the nitrogen‐rich composition of the macromolecule‐enriched electrolyte (MEE) fosters the formation of robust nitride interphases that impart enduring stability to both the cathode and anode. As a result, the hard carbon (HC) || NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) full cells demonstrate significant rechargeability even with an ultrahigh cutoff voltage of 4.4 V. Our approach distinctively avoids the use of fluorinated molecules typically found in (localized‐) high‐concentration electrolytes, presenting a novel principle that could revolutionize high‐voltage electrolyte design.

Lithium-ion batteries (LIBs) have been widely adopted in the automotive industry, with an annual global production exceeding 1000 GWh. Despite their success, the escalating demand for LIBs has created concerns on supply chain issues related to key elements, such as lithium, cobalt, and nickel. Sodium-ion batteries (SIBs) are emerging as a promising alternative due to the high abundance and low cost of sodium and other raw materials. Nevertheless, the commercialization of SIBs, particularly for grid storage and automotive applications, faces significant hurdles. This perspective article aims to identify the critical challenges in making SIBs viable from both chemical and techno-economic perspectives. First, a brief comparison of the materials chemistry, working mechanisms, and cost between mainstream LIB systems and prospective SIB systems is provided. The intrinsic challenges of SIBs regarding storage stability, capacity utilization, cycle stability, calendar life, and safe operation of cathode, electrolyte, and anode materials are discussed. Furthermore, issues related to the scalability of material production, materials engineering feasibility, and energy-dense electrode design and fabrication are illustrated. Finally, promising pathways are listed and discussed toward achieving high-energy-density, stable, cost-effective SIBs.