Surface layer formation of LiCoO2 thin film electrodes in non-aqueous electrolyte containing lithium bis(oxalate)borate

► In situ FTIR in the electrolyte containing LiBOB were performed. ► Adsorption of BOB anion was confirmed more positive potential than 4.0 V vs. Li. ► LiPF6 solution formed relatively thick surface layer. ► Surface layer formed in LiBOB solution was very thin. ► BOB anion prevents the growth of the surface layer.