Thermal runaway is the most important safety problem of the lithium ion battery. A thermal model combined five side reactions is established to analyze the high temperature distribution change of the separator during the local thermal runaway process of a lithium-ion battery cell with local heating terminals in this paper. The results show that thermal runaway will not be triggered inside a battery cell if a balance of the heat convection between the battery cell and the air forms when a single terminal is heated with 423.15 K. And local thermal runaway can be triggered when the both terminals of the battery cell are heated with 473.15 K and 423.15 K. In addition, the temperature distribution of the separator layer shows an extension trend along the horizontal direction firstly and then along the vertical direction, and local heating makes a big temperature difference inside a battery cell.

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