Abstract
We evaluated charge-discharge behavior of four graphite electrodes—raw synthetic graphite (SG), shaped natural graphite (NG), soft carbon-coated natural graphite (SCNG), and hard carbon-coated natural graphite (HCNG)—in a 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) ionic liquid containing lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). According to charge-discharge curves at the first cycle in LiTFSI/EMImFSI, a capacity loss by an irreversible reaction was observed for cells with SG and SCNG, whereas the capacity loss for cells with NG and HCNG was relatively small. Coulombic efficiency with the cell cycling also proved that charge-discharge behavior of the graphite electrodes in LiTFSI/EMImFSI is strongly affected by surface structure of the graphite active materials and that basal-plane-oriented graphite, such as NG and HCNG, can reduce the loss of primary charge capacity.