Influences of Instant Voltage Drop Occurring during Insulation Test on Performance of Lithium Ion Batteries

Effects of partial discharge during an insulation test were investigated with jelly rolls of a single electrode pair and 500 mAh stacking-type cells by inspecting the separator and studying the capacity fade of the cells prepared with the tested 500 mAh jelly rolls. For comparison, 500 mAh cells with jelly rolls without insulation test or with separator having laser-engraved holes are also prepared. The cells prepared with jelly rolls with insulation test show higher capacity fading rate than cells comprised with jelly rolls without insulation test and lower fading rate than those assembled with jelly rolls with laser-engraved separator. Dark spots were observed on the negative electrodes at the corresponding position facing the defect spots on the separator caused by partial discharge or the laser-engraved holes in a glovebox and became white after being moved into air accompanied with a temperature rise. Li2O was also detected with XPS in addition to Li2CO3, and higher Li content was found by LIBS at th...