Application of ionic liquid as K-ion electrolyte of graphite//K2Mn[Fe(CN)6] cell

Hiroo Onuma, Kei Kubota, Shotaro Muratsubaki, Tomooki Hosaka, Ryoichi Tatara, Takayuki Yamamoto, Kazuhiko Matsumoto, Toshiyuki Nohira, Rika Hagiwara, Hiroshi Oji, Satoshi Yasuno, Shinichi Komaba

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)2849-2857
Number of pages9
JournalACS Energy Letters
Issue number9
Publication statusPublished - 11 Sep 2020


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