A Depth-profiling Study on Solid Electrolyte Interface: Bis(fluorosulfuryl)imide Anion toward Improved K+ Storage

Solid electrolyte interface (SEI) significantly affects alkaline metal ion battery performance in terms of reversible capacity, columbic efficiency and cycling stability. However, intrinsic properties of SEI layer in potassium ion batteries (KIBs), including structures, components, formation mechanism and corresponding K+ storage behavior, are poorly understood. Here, we focus on the effect of electrolyte on SEI formation and K+ storage behavior in self-supported nitrogen-doped graphite foams (NGFs). Two types of organic electrolytes, KPF6 and KN(SO2F)2 (KFSI) salt in EC/DEC solution, were carefully selected and compared in detail to reveal the effect of SEI on K+ ion storage mechanism. The experimental results, including in-situ electrochemical evaluations and depth-profiling XPS analysis, demonstrate that the salts of KFSI result in a more uniform, stable and thinner SEI layer compared with the SEI induced by KPF6. Particularly, the KFSI-induced SEI is rich in stable and uniformly distributed inorganic ...