As the cathode materials in conversion-type lithium ion batteries, transition-metal chlorides are well-known to easily dissolve in many organic solvents. However, the LiPF6/methyl difluoroacetate (MFA; CHF2COOCH3) electrolyte is effective in suppressing the dissolution of the CuCl2 electrode, as reported for a Li/CuCl2 battery. This effect did not arise in the MFA solvent without LiPF6, but did on slightly dissolving LiPF6 in the MFA solvent. This was because a very small amount of film was formed on the surface of the CuCl2 electrode due to the addition of the small amount of LiPF6, and the film was composed of copper fluoride hydroxide, partial release of Cl from CuCl2, and CuCl.