Electrochemical Intercalation of Cesium into Graphite in Ionic Liquid Electrolyte (Supporting Information)

Graphite is widely used as the negative electrode for alkali-metal ion secondary batteries because of its ability to accommodate various ions between its graphene layers resulting in the formation of graphite intercalation compounds (GICs). In this study, we investigated the intercalation of Cs+ ions into graphite using an ionic liquid (IL)-based electrolyte, Cs[FTA]–[C4C1pyrr][FTA] (FTA = (fluorosulfonyl)(trifluoromethylsulfonyl)amide, C4C1pyrr = N-butyl-N-methylpyrrolidinium). In this electrolyte, the graphite negative electrode imparted an initial reversible capacity of 180 mAh g−1 at 298 K. The formation of Cs-GICs was analyzed using an X-ray diffraction technique to reveal the formation of stage-1 CsC8. The formation potentials of various alkali metal GICs were also compared with respect to the potential of ferrocenium/ferrocene redox couple, revealing that these GICs particularly for stage-1 compounds form in a similar potential range with small differences of 0.2–0.3 V.

石墨烯因其能够在石墨烯层间容纳多种离子，从而形成石墨插层化合物（GICs）而广泛用作碱金属离子二次电池的负极材料。在本研究中，我们采用基于离子液体（IL）的电解质Cs[FTA]–[C4C1pyrr][FTA]（其中FTA代表氟磺酰基三氟甲磺酰亚胺，C4C1pyrr代表N-丁基-N-甲基吡咯啶阳离子）研究了铯离子（Cs+）在石墨烯中的插层行为。在此电解质中，石墨负极在298 K下表现出初始可逆容量为180 mAh g−1。利用X射线衍射技术分析了Cs-GICs的形成，揭示了第一阶段CsC8的形成。此外，通过与铁卟啉/铁卟啉氧化还原对的电位进行比较，各种碱金属GICs的形成电位也得到了分析，结果表明，这些GICs尤其是第一阶段化合物，在相似电位范围内形成，存在0.2–0.3 V的小幅差异。