Achieving stable potassium-ion batteries by regulating solvent-cation-anion interactions

In the low-concentration potassium bis(fluorosulfonyl)imide (KFSI)/1,2-diethoxyethane (DEE) electrolyte, the interactions between the DEE, potassium ion (K⁺) and FSI^- anion (DEE-K⁺-FSI^-) are unique, compared to 1,2-dimethoxyethane (DME)-K⁺-FSI^- (DME-K⁺-FSI^-), DEE-lithium ion (Li⁺)-FSI^- and DME-Li⁺-FSI^-. This uniqueness is reflected not only in the greater involvement of FSI^- in the interfacial reactions that form a stable solid-electrolyte interphase, but also in the possible preferential simultaneous desolvation of the two DEE molecules as a whole over FSI^- from the K⁺[DEE]₂[FSI^-] solvation structure, which could be the reason for solvent co-intercalation into graphite for the LiFSI/DEE and KFSI/DME electrolytes.