Electrolyte design and interface engineering for high-voltage solid-state lithium batteries

Solid-state lithium batteries (SSLBs) have attracted extensive attention as next-generation energy-storage systems because they offer improved safety and the possibility of coupling lithium metal anodes with high-energy cathodes. Among the many development directions of SSLBs, high-voltage systems are particularly important because they provide a direct pathway toward higher energy density. However, under high-voltage operation, typically above approximately 4.3 V versus Li⁺/Li but strongly dependent on cathode chemistry and state of charge, both the solid electrolyte and the electrode/electrolyte interface are subjected to severe electrochemical and structural challenges. Electrolyte oxidation, cathode-induced interfacial decomposition, space-charge effects, mechanical contact loss, and manufacturing difficulties jointly limit the practical performance of high-voltage SSLBs. This review systematically summarizes recent advances in electrolyte design for high-voltage SSLBs, covering inorganic solid electrolytes, polymer electrolytes, organic-inorganic composite electrolytes, gel polymer electrolytes, and quasi-solid-state electrolytes. In addition, the critical role of interface engineering is discussed with emphasis on cathode-side stabilization strategies, interphase regulation, and coating design. Finally, the major challenges and future research directions for high-voltage SSLBs are presented. The development of high-voltage SSLBs requires synergistic optimization of electrolyte chemistry, interfacial stability, and scalable processing strategies.