What is the reason for high temperature swelling of soft pack lithium batteries?

　　1. Thickness variation of electrode plates: During the charging process of lithium-ion batteries, the increase in cell thickness is mainly due to the expansion of the negative electrode, especially the expansion of graphite materials, which can reach an expansion rate of about 10%. The formation of SEI film, charge state, process parameters, and other factors such as adhesive strength, charge discharge rate, etc. can all affect the expansion rate.

　　2. Inflation caused by battery gas production: Gas production inside the battery is another important cause of battery swelling. This may occur during the first charge and discharge process of the battery, as the electrolyte undergoes a reduction reaction on the electrode surface to form an SEI film, while producing gases such as CO and C2H4. DMC and EMC in solvents also generate gases during the film formation process. In addition, the decomposition of LiPF6 in the electrolyte may produce PF5, which in turn promotes the decomposition of the electrolyte and generates more gases.

　　3. Abnormal processes can lead to gas generation: poor packaging, damage to Pocket surface, corner damage, excessive water content inside the battery cell, abnormal formation process, unstable SEI film, overcharging or overdischarging, short circuit, and corrosion can all cause gas generation inside the battery, leading to bloating.

　　4. Electrolyte additives: Experiments have shown that the use of electrolyte additives containing 3% VC (vinyl carbonate) can significantly improve the gas swelling problem of soft pack lithium batteries at high temperatures. This may be because VC helps to form a more stable SEI film and reduce gas generation.

　　5. Process optimization: By optimizing the process technology, such as allowing it to stand at different temperatures after injection, the phenomenon of gas expansion at high temperatures can be effectively suppressed, improving the stability and performance of the battery.

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