Suppression of Co-Intercalation Reaction of Propylene Carbonate and Lithium Ion into Graphite Negative Electrode by Addition of Diglyme

Suppression of a co-intercalation reaction into a graphite negative electrode is an important issue to use propylene carbonate (PC) as a base electrolyte solvent in lithium-ion batteries. In order to suppress the co-intercalation reaction, diethylene glycol dimethyl ether (diglyme) was added to the PC-based electrolyte solution. Interfacial reactions at the graphite negative electrodes were investigated by an in-situ scanning probe microscope (SPM) observation and an in-situ Raman spectroscopy to elucidate effects of diglyme in the PC-based electrolyte solution. Reversible intercalation and de-intercalation reactions of lithium ion took place in the PC-based electrolyte solution by adding small amount of diglyme (PC:diglyme = 20:1, vol. ratio). Based on the results of in-situ SPM and in-situ Raman spectroscopy, it is found that diglyme-solvated lithium ion preferentially intercalated and decomposed within the graphite and form a surface film. This surface film lowered the co-intercalation reaction potential of PC-solvated lithium ion, and co-intercalated PC-solvated lithium ion was easily decomposed within the graphite and then formed the effective surface film on the graphite surface.