Potassium-ion batteries using KFSI/DME electrolytes: Implications of cation solvation on the K+-graphite (co-)intercalation mechanism

Recently potassium-ion batteries have been proposed as a promising next generation battery technology owing to cost effectiveness and wide range of electrode materials well electrolytes available. Potassium bis(fluorosulfonyl)imide (KFSI) in monoglyme (DME) is one potential electrolyte, wherein the K+ solvation heavily depends on salt concentration strongly affects electrochemistry. Pure intercalation occurs for highly concentrated (HCEs), while co-intercalation dominant less electrolytes. The mechanisms are easily distinguished by their galvanostatic curves operando XRD. Here Raman spectroscopy coupled with computational chemistry used provide in-depth knowledge about cation range, all way up 5 M KFSI DME. Starting from pure DME experimental computed spectra provides detailed conformational assignment enabling us calculate number (SN) function For low medium concentrations, SN approximately constant, ca. 2.7, and/as there surplus solvent available, HCEs, much <2. This reduced results thermodynamically more favored desolvation at graphite surface, leading intercalation, compared higher conventional co-intercalation, observed also electrochemical cycling.