High temperature test in simulated environment can be conducted by hot box test. The hot box test is to simulate the improper use of the battery under high temperature, such as placing the mobile phone in a sun exposed car, or placing the mobile phone or electronic products in a microwave oven, and the temperature can reach 130 ℃ or even 150 ℃. In case of heat abuse, the heat source is not only from the positive and negative electrode materials inside the battery and their reaction with electrolyte, but also from the positive and negative electrode short circuit caused by melting and shrinking of the isolation film at high temperature. Joule heat generated by short circuit is also an important heat source during hot box test. Table 2 summarizes the thermal behavior of lithium ion battery system in a certain temperature range when the electrolyte system is 1mol/L LiPF6/(PC+EC+DMC).

　　When the temperature is between 90 ℃ and 120 ℃, the metastable layer of the solid electrolyte interface film (SEI) formed on the surface of the carbon negative electrode by multiple charges and discharges first decomposes and releases heat; With the increase of temperature, the heat absorption of diaphragm melts successively; When the temperature is 180~500 ℃, the positive electrode and the electrolyte have a strong exothermic reaction and produce gas; The SEI film can prevent the interaction between the lithium embedded carbon and the organic electrolyte. When the temperature is higher than 120 ℃, the SEI film breaks and cannot protect the negative electrode. The negative electrode material may start to exothermic react with the solvent and generate gas. When the temperature rises to 240~350 ℃, the fluorine containing binder starts to react with the lithium embedded carbon in a violent chain growth reaction, which releases a lot of heat. The reaction between the negative electrode and the electrolyte may deplete lithium, so this reaction will not occur; If the temperature continues to rise to 660 ℃, the Al collector will undergo endothermic melting. These conditions are very dangerous for large lithium-ion power batteries, affecting the battery life and safety.

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