Electrochemical preparation of a lithium-graphite-intercalation compound in a dimethyl sulfoxide-based electrolyte containing calcium ions

Electrochemical preparation of lithium-graphite-intercalation compound in dimethyl sulfoxide (DMSO)-based electrolytes containing calcium salt was studied. Intercalation of DMSO-solvated cation took place in 1.0 mol dm−3 lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) + 1.5 mol dm−3 calcium bis(trifluoromethanesulfonyl)amide (Ca(TFSA)2)/DMSO, whereas intercalation of Li+ ions without solvent took place in 1.0 mol dm−3 LiTFSA + 2.5 mol dm−3 Ca(TFSA)2/DMSO. Raman spectroscopic study suggests absence of free DMSO in 1.0 mol dm−3 LiTFSA + 2.5 mol dm−3 Ca(TFSA)2/DMSO, which can lead to different solvation structure of Li+ from the one in 1.0 mol dm−3 LiTFSA + 1.5 mol dm−3 Ca(TFSA)2/DMSO. Factors that are responsible for co-intercalation and only Li+ ion intercalation are discussed based on the Li+ ion solvation structures.