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

Abstract

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.