Effect of Li₂CO₃ additive on gas generation in lithium-ion batteries

To elucidate the mechanism of gas generation during charge-discharge cycling of a lithium-ion cell, the generated gases and passive films on the carbon electrode are examined by means of gas chromatography (GC) and Fourier transform infrared (FTIR) spectroscopy. In ethyl carbonate/dimethyl carbonate and ethyl carbonate/diethyl carbonate 1 M LiPF₆ electrolytes, the detected gaseous products are CO₂, CO, CH₄, C₂H₄, C₂H₆, etc. The FTIR spectrum of the surface of the carbon electrode shows bands which correspond to Li₂CO₃, ROCO₂Li, (ROCO₂Li)₂, and RCO₂Li. These results suggest that gas evolution is caused by electrode decomposition, reactive trace impurities, and electrolyte reduction. The surface of the electrode is composed of electrolyte reduction products. When 0.05 M Li₂CO₃ is added as an electrolyte additive, the total volume of generated gases is reduced, and the discharge capacity and the conductivity of lithium-ions are increased. These results can be explained by a more compact and thin 'solid electrolyte interface' film on the carbon electrode formed by Li₂CO₃, which effectively prevents solvent co-intercalation and carbon exfoliation.