Effect of internal resistance difference (IRD) on the safety performance of lithium-ion battery pack with different attended modes was investigated. The testing indicated that with increase of cycle times

for cell with IRD its internal resistance and housing temperature increased gradually and the discharge capacity decreased unceasingly

leading to continuous enlargement of IRD and the failure of the cell at last. These results indicated that IRD is an important factor affecting the safety performance for lithium-ion battery pack. Compared with normal cell

for a cell pack

the bigger the IRD the worse the safety performance. The safety performance is better for the pack with parallel connection than for that with series connection.