Aging of lithium-ion battery separators during battery cycling

The separator is a core component of lithium-ion batteries, and its service life impacts the electrochemical performance and device safety. This study reports the performance of aluminum oxide ceramic-coated polyethylene separators (PE-Al2O3 separators) before and after aging. During lithium-ion battery cycling, degradation products from the electrolyte and graphite were found at the separator surface, leading to a decrease in porosity and ionic conductivity and an increase in the internal resistance of the separator. The mechanical properties of the separators gradually deteriorated with the increase in current rates and the number of cycles. After 200 cycles at 1.5C, the tensile strength of the aging separator decreased by about 6.70 % compared with the fresh separator. The contact angle between the separator and the electrolyte increased from 15.2° to 24.4°, over the first 200 cycles at 1.5C, and the wettability deteriorated with the aging of the separator. In addition, on aging, the separator maintained a stable thermal decomposition temperature and showed stable chemical properties.