Battery systems enabling sustainable high energy output at elevated temperatures are highly desirable, especially in high-temperature (HT) environments or hot regions. Sodium metal batteries are attractive next-generation battery technologies with low production costs and high energy densities. The exacerbated detrimental side reactions between the sodium metal anode and the liquid electrolyte at HT, however, reduce sodium plating/stripping reversibility and shorten the cycle life. Ether-based electrolytes are highly compatible with the sodium metal anode, promising good HT electrochemical performances. Nonetheless, the correlation between the molecular structures of ether solvents and HT sodium reversibility has been poorly established because of the complex interfacial reactions. In this study, conventionally used cyclic and linear ethers have been paired with fluorine-rich sodium salt to formulate electrolytes for systematic study. We have revealed that linear ethers outperform cyclic ethers at HT because of their improved thermal stability. Among them, the electrolyte based on diglyme with an appropriate molecular structure delivers the best performance. It strikes a balance in the coordination strength between Na⁺ and the solvent, which ensures adequate participation of anions in the solvation sheath while reducing the solvent’s electrochemical activity for reductive decomposition at HT. Consequently, it induces the formation of an inorganic-rich solid–electrolyte interphase with compositional uniformity, excellent ionic conductivity, and high mechanical strength. Thus, a high sodium plating/stripping coulombic efficiency of 99.9% has been achieved at a high current density of 5 mA·cm⁻². As-formulated anode-free sodium metal batteries maintain 80% of the initial capacity after 150 charge/discharge cycles at 60 °C.

Organosulfur materials containing sulfur–sulfur bonds are an emerging class of high-capacity cathodes for lithium storage. However, it remains a great challenge to achieve rapid conversion reaction kinetics at practical testing conditions of high cathode mass loading and low electrolyte utilization. In this study, a Li-rich pyrolyzed polyacrylonitrile/selenium disulfide (pPAN/Se₂S₃) composite cathode is synthesized by deep lithiation to address the above challenges. The Li-rich molecular structure significantly boosts the lithium storage kinetics by accelerating lithium diffusivity and improving electronic conductivity. Even under practical test conditions requiring a lean electrolyte (Electrolyte/sulfur ratio of 4.1 μL mg⁻¹) and high loading (7 mg cm⁻² of pPAN/Se₂S₃), DL-pPAN/Se₂S₃ exhibits a specific capacity of 558 mAh g⁻¹, maintaining 484 mAh g⁻¹ at the 100th cycle with an average Coulombic efficiency of near 100%. Moreover, it provides (electro)chemically stable Li resources to offset Li consumption over charge–discharge cycles. As a result the as-fabricated anode-free cell shows a superior cycling stability with 90% retention of the initial capacity over 45 cycles. This study provides a novel approach for fabricating high-energy and stable Li–SPAN cells.

The ever-growing pursuit of high energy density batteries has triggered extensive efforts toward developing alkali metal (Li, Na, and K) battery (AMB) technologies owing to high theoretical capacities and low redox potentials of metallic anodes. Typically, for new battery systems, the electrolyte design is critical for realizing the battery electrochemistry of AMBs. Conventional electrolytes in alkali ion batteries are generally unsuitable for sustaining the stability owing to the hyper-reactivity and dendritic growth of alkali metals. In this review, we begin with the fundamentals of AMB electrolytes. Recent advancements in concentrated and fluorinated electrolytes, as well as functional electrolyte additives for boosting the stability of Li metal batteries, are summarized and discussed with a special focus on structure–composition–performance relationships. We then delve into the electrolyte formulations for Na- and K metal batteries, including those in which Na/K do not adhere to the Li-inherited paradigms. Finally, the challenges and the future research needs in advanced electrolytes for AMB are highlighted. This comprehensive review sheds light on the principles for the rational design of promising electrolytes and offers new inspirations for developing stable AMBs with high performance.