Insight into the Gassing Problem of Li-ion Battery

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. In overcharging, the gassing occurs mainly through the electrochemical oxidation of electrolyte solvents on the cathode with the Li ions from the electrolyte being reduced into metallic Li on the anode. In overheating, the gassing takes place through not only the redox decomposition but also the chemical decomposition of the electrolyte solvents on both the anode and cathode besides the vapor expansion of volatile electrolyte solvents. In this opinion article, only the gas generation occurring under the normal operation and storage conditions will be addressed. 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. The chemical decomposition of dialkyl carbonate solvents produces ether and CO2, as described by Eq. 1, which can take place on both the anode and cathode. Resulting CO2 can be reduced into CO in accompany with the consumption of Li ions that are eventually originated from the cathode either by the chemical reduction (Eq. 2) or by the electrochemical reduction (Eq. 3) on the anode. R1O C OR2 O