A comparative study on safety and electrochemical characteristics of cylindrical lithium-ion cells with various formats

The present work carries out a comparative study to illustrate the safety performance of two new-format cells (22650 and 26650) in the thermal runaway tests induced by over-heating and overcharge tests, referred by the traditional 18650 cells. In addition, a long-term cycling test is also performed to evaluate the electrochemical characteristics of the three cells. When charged to the same capacity (1700 mAh), the cell with a larger size demonstrates comparative gentler thermal runaway behaviors during the over-heating, with a longer time to thermal runway and a higher temperature to thermal runaway. The thermal runaway of the fully charged 26650 cell lags behind that of 18650 and 22650 cells in the over-heating tests; that is, the 26650 cell shows the best thermal safety performance among the three kinds of cells. The safety performance of the 26650 cell is also more competitive than 18650 and 22650 cells during overcharging, with a larger SOC_end illustrated when the interior safety devices take effects. At last, the 26650 cell shows more promising electrochemical features, demonstrating a larger absolute capacity and a slighter degradation over the long-term cycling, in comparison with 18650 and 22650 cells.