INTERNAL SHORT CIRCUIT IN LITHIUM-ION BATTERIES

Repeatable methods for introducing minor defects in commercial Li-ion pouch cells were developed and different studies were conducted to compare the different signatures that would provide information regarding the factors that are most critical to detect the onset of internal short circuit for each defect test. The cells were subjected to overcharge, over-discharge, nail indentation and heating defect tests. After defect introduction, three different studies – cycling, thermal runaway, and self-discharge were performed on the cells. The overcharge defect case showed signatures in all three studies with the major cause of these signatures being lithium dendrite formation that led to reduction in capacity. The overcharge case was also unique in that it showed recovery in capacity due to lithium stripping process and had the highest temperature recorded which proves that it had the most dangerous defect case. The over-discharge case showed signs of possible copper deposition on the anode side which was evident by the presence of lithium plating in patches which could have been due the copper deposition locations becoming active sites for lithium plating. The nail indentation defect case showed signatures in the thermal runaway study by the shortest time it took to go into thermal runaway and in the self-discharge study which was shown by the inability of cells to stay at a stable voltage even at the most stable SOC. The heating defect test showed potential in that it was able to melt the separator near the pouch and that it had a lower temperature for onset of exotherm, but improvements need to be made to get more conclusive results for this defect case.