Swelling mechanism of 0%SOC lithium iron phosphate battery at high temperature storage

The storage performances of 0% SOC and 100%SOC lithium iron phosphate (LFP) batteries are investigated. 0%SOC batteries exhibit higher swelling rate than 100%SOC batteries. In order to find out the source of battery swelling, cathode and anode electrodes obtained from 0%SOC battery are evaluated separately. By analyzing the results, the anode is identified as the main source of battery swelling. The 0%SOC anodes are then stored with different solvents of electrolyte and gas chromatography is utilized to analyze the main components of the gas products. Moreover, different types of anodes are also investigated. A three-electrode system is designed to study the voltage change during charging and discharging process. The results confirm that the battery swelling is related to the voltage state of the anode. The anode is unstable at high voltage which may cause the decomposition of SEI during storage process. After SEI decomposes, the fresh anode surface will be exposed to the electrolyte, and the new SEI will be formed to generate large amount of gas which can cause the battery swelling. Finally, different SOCs of LFP batteries are investigated. It is found that the swelling rate tends to be stable at 30% SOC.