Application of Ionic Liquid as K-Ion Electrolyte of Graphite//K₂Mn[Fe(CN)₆] Cell

Abstract

A binary ionic liquid of K­[FSA]-[C3C1pyrr]­[FSA] (2:8 in molar ratio) in which N-methyl-N-propylpyrrolidinium and bis­(fluorosulfonyl)­amide are abbreviated as [C3C1pyrr] and [FSA], respectively, is applied as an electrolyte of K-ion batteries for the first time. A graphite composite electrode with sodium carboxymethylcellulose as the binder undergoes reversible potassium intercalation, forming a KC8 compound in a K half-cell filled with the binary ionic liquid as electrolyte. Because the K­[FSA]-[C3C1pyrr]­[FSA] does not corrode an Al foil current collector even with polarization of up to 6 V versus K+/K, a K2Mn­[Fe­(CN)6] positive electrode yields a highly reversible capacity of 134 mAh g–1 at ca. 4.0 V. We demonstrate a K-ion battery of graphite//K2Mn­[Fe­(CN)6] configuration with an ionic liquid electrolyte that exhibits stable charge and discharge properties over 200 cycles at room temperature. The redox performance is significantly improved by replacing the conventional KPF6 carbonate ester solution with the ionic liquid.

Recent Progress in Electrolyte Development and Design Strategies for Next‐Generation Potassium‐Ion Batteries

“…The commonly used IL cations are imidazolium (e. g., [EMIM] + ), pyrrolidinium (e. g., PYR14), ammonium (e. g., [DEME] + ), and sulfonium (e. g., [Me 3 S] + ), whereas the typically employed IL anions are tetrafluoroborate (BF 4 − ), bis(trifluoromethanesulfonyl)imide (TFSI − ), and bis(fluorosulfonyl)imide (FSI − ). IL electrolytes based on potassium bis(trifluoromethanesulfonyl) amide (PTFSA) has been reported for high‐voltage PIBs [89] . Because these electrolytes can operate up to a potential of around 6.0 V, they can be safely used at high voltages.…”

“…Because these electrolytes can operate up to a potential of around 6.0 V, they can be safely used at high voltages. The physicochemical properties of KTFSA‐based ILs are presented in Figure 11 [89] . Using the same electrolyte, Masese et al.…”

The Quest for Stable Potassium‐Ion Battery Chemistry

“…As discussed, K 2 Mn[Fe(CN) 6 ] cathodes have yet to demonstrate stable long cycling life in non‐aqueous carbonate electrolytes. [ 28,29,48–50 ] Goodenough and co‐workers first reported that K 2 Mn[Fe(CN) 6 ] could deliver a high capacity of ≈140 mAh g −1 but showed short cycling of 100 cycles. [ 28 ] Later, Komaba and co‐workers, Sun and co‐workers, and other researchers made progress to extend its cycling stability by optimizing electrolytes or electrode structures; however, the cycling was still limited to 500 cycles.…”

“…[ 28 ] Later, Komaba and co‐workers, Sun and co‐workers, and other researchers made progress to extend its cycling stability by optimizing electrolytes or electrode structures; however, the cycling was still limited to 500 cycles. [ 29,49,50 ]…”

Effect of Crystallinity of Synthetic Graphite on Electrochemical Potassium Intercalation into Graphite

“…Indeed, the electrochemical potassium intercalation properties of the graphite electrode are highly dependent on cell components such as electrode and electrolyte used in K cells. In recent years, our group studied the influences of binder 3 and electrolytes [7][8][9][10] to demonstrate a large reversible capacity of the graphite electrode in a K cell, approaching its theoretical capacity of 279 mAh g -1 . 2 Under the optimized evaluation condition, in this study, we investigate the effects of the graphite material itself on the potassium intercalation properties.…”