Charge–Discharge Behavior of Graphite Negative Electrodes in FSA-Based Ionic Liquid Electrolytes: Comparative Study of Li-, Na-, K-Ion Systems

K-ion batteries utilizing ionic liquid (IL) electrolytes are promising candidates for next-generation because of the abundance potassium resources, low redox potential potassium, and high safety ILs. Our major interest is in comprehensive understanding electrochemical alkali metal intercalation/deintercalation into graphite negative electrodes, can easily form intercalation compounds (GICs) with various species, but not sodium. In this study, we investigated storage mechanism electrodes bis(fluorosulfonyl)amide (FSA)-based ILs, compared GIC formation Li-, Na-, systems. Charge–discharge tests K[FSA]–[C 3 C 1 pyrr][FSA] IL (C pyrr = N -methyl- -propylpyrrolidinium) at 313 K yielded an initial discharge capacity as 268 mAh (g-C) −1 , leading to several K-GICs including stage-3 KC 36 stage-2 24 stage-1 8 . The rate capability long-term cycling indicated stable potassiation/depotassiation behavior 225 cycles. A comparison among M[FSA]–[C (M Li, Na, K) ILs 298 that binary M-GICs localized range below −2.85 V vs. Fc + /Fc (Fc ferrocene), which possibly hinders Na-GIC formation.