Mechanism of gas evolution from the cathode of lithium-ion batteries at the initial stage of high-temperature storage

The evolution of gas in lithium-ion batteries (LIBs) at a charged state is one of the main problems in the industry because it causes significant distortion or swelling of the batteries. The mechanism of the gas-generating reaction related to the cathode at a charged state of LIBs was investigated. A side reaction between the electrolyte solution and free lithium compounds, such as Li₂CO₃ or LiOH in the cathode, is considered as the main cause of gas evolution at early stages of the storage test. Both Li ₂CO₃ and LiOH generated CO₂ mainly by a HF-mediated reaction, but the evolution of CO₂ could be triggered by addition of H₂O without a fluorine source for LiOH. Ni-based cathode materials generated more gas than conventional LiCoO₂ at the initial stage because they contain more free lithium compounds, but the rate of gas evolution slowed down with time, suggesting that Ni-based active materials might be more appropriate for reducing long-term gas evolution in LIBs if the free lithium compounds could be removed effectively from the surface.