Gas generation (namely, the volume swelling of battery, or called the gassing) is a common phenomenon of the degradation of battery performance, which is generally a result of the electrolyte decomposition occurring during the entire lifespan of Li-ion batteries no matter whether the battery is in service or not. Abuse conditions such as overcharging and overheating make the gassing worse or even result in disastrous accidents.
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Assuming that the Li-ion battery is well formed in manufacture and properly operated in service, the gas generation can be attributed to the chemical decomposition and redox decomposition of the electrolyte solvents on the anode and cathode.
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In particular, the chemical decomposition is increased with the temperature, and the redox decomposition is increased with the state-of-charge (SOC) of battery.
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For the gas generation caused by the redox decomposition of electrolyte solvents on two electrodes, Figure 1 shows that the swelling ratio of a graphite/LiCoO2 cell remains nearly constant when the SOC is lower than 80%, however, dramatically increases as the SOC exceeds 80% (Lee et al., 2003).
