Effect of lithium carbonate precipitates on the electrochemical cycling stability of LiCoO₂ cathodes at a high voltage

An electrolyte (LiPF₆-EC/PC/DEC) containing a lithium carbonate (Li₂CO₃) additive is used to enable the high cycling stability of a lithium cobalt oxide (LiCoO₂) cathode which is charged to 4.5 V for a higher capacity. A capacity as high as 162.8 mA h g^-1 (1 C) is maintained after 116 cycles, which is twice as high as the capacity of 88.5 mA h g^-1 which was achieved in the Li₂CO₃ free instance. The interface properties of the electrode are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. It is found that the solid electrolyte interphase (SEI) film tends to be thin and steady, and that the electrolyte decomposition is suppressed with the addition of Li₂CO₃. A possible mechanism is proposed according to the DFT calculation. The results indicate that the Co⁴⁺...CO₃^2- coordination may decrease the oxidizability of Co⁴⁺ on the electrode surface so that the electrolyte decomposition could be suppressed.