Electrochemical intercalation of lithium into graphite: Influence of the solvent composition and of the nature of the lithium salt

The electrochemical intercalation of lithium into graphite was studied in various electrolytes containing chloroethylene carbonate (ClEC), ethylene carbonate (EC) and propylene carbonate and their mixtures as solvents and LiClO4, LiBF4 and LiAsF6 as lithium salts. The reduction of ClEC and EC, catalyzed on the surface of the graphite electrode, starts at potentials equal to 1.7 and 0.9 V, respectively, and leads to the formation of reduction products which passivate the carbon surface. The effect of the nature of the lithium salts on the properties of the interfacial layer is also examined. With LiBF4, the first reduction of the carbon electrode results in a massive reduction of the electrolyte, especially LiBF4, that limits the reversible lithium intercalation. With the electrolytes containing ClEC, the reversible intercalation is observed with formation of LiC6. Moreover, a slight excess of capacity compared with LiC6 is observed after the first cycle. It could be attributed to an extra fixation of lithium in the interphase layer generated by C-Li(ads.)-Cl bonds. (C) 1998 Elsevier Science Ltd. All rights reserved.