Studies of the passivation film as a function of the concentration of electrolyte in lithium-ion battery

The irreversible capacities caused by the reduction of solvent on the surfa ce of a negative electrode (KMFC: Kawasaki Mesophase Fine Carbon) were exam ined during the initial cycle in ethylene carbonate (EC)-diethyl carbonate (DEC) electrolyte solutions at various concentrations of LiPF6. Chronopoten tiograms, linear sweep voltammograms, and impedance spectra clearly showed differences in irreversible capacity and that those differences are related to the concentration of electrolyte during the initial charge. These diffe rences were caused by the amount of solvent decomposition as a function of the concentration of LiPF6 electrolytic salt. The data are discussed with r eference to the concentration of electrolytic salt and the properties of pa ssivation film formed by solvent decomposition.