Recent fluorination strategies in solid electrolytes for high-voltage solid-state lithium-ion batteries

High-voltage solid-state lithium-ion batteries (SSLIBs) have attracted considerable research attention in recent years due to their high-energy-density and superior safety characteristics. However, the integration of high-voltage cathodes with solid electrolytes (SEs) presents multiple challenges, including the formation of high-impedance layers from spontaneous chemical reactions, electrochemical instability, insufficient interfacial contact, and lattice expansion. These issues significantly impair battery performance and potentially lead to battery failure, thus impeding the commercialization of high-voltage SSLIBs. The incorporation of fluorides, known for their robust bond strength and high free energy of formation, has emerged as an effective strategy to address these challenges. Fluorinated electrolytes and electrode/electrolyte interfaces have been demonstrated to significantly influence the reaction reversibility/kinetics, safety, and stability of rechargeable batteries, particularly under high voltage. This review summarizes recent advancements in fluorination treatment for high-voltage SEs, focusing on solid polymer electrolytes (SPEs), inorganic solid electrolytes (ISEs), and composite solid electrolytes (CSEs), along with the performance enhancements these strategies afford. This review aims to provide a comprehensive understanding of the structure-property relationships, the characteristics of fluorinated interfaces, and the application of fluorinated SEs in high-voltage SSLIBs. Further, the impacts of residual moisture and the challenges of fluorinated SEs are discussed. Finally, the review explores potential future directions for the development of fluorinated SSLIBs.