1. In the initial stage of lithium-ion battery charging, when the current passes through the battery, a part of electric energy is converted into heat energy, and ohmic polarization also produces a part of heat, but the surface temperature of the battery rises very slowly. When the battery reaches full charge state, the continuous intercalation reaction of lithium ions becomes the deposition of lithium metal on the negative surface, and the solvent is oxidized (heat released by the oxidation reaction of solvent caused by overcharge). The amount of heat released by lithium ion reacting with solvent is much higher than that of reversible state.) The heat released from lithium ion reacting with solvent heated the battery; with the increase of battery temperature, the reaction of lithium metal reacting with solvent, lithium intercalation carbon reacting with solvent occurs successively, and the heat runs out of control, accompanied by solvent decomposition, binder reacting with lithium metal.

2. When lithium-ion batteries are heated, the reactions inside the batteries are like a chain of reactions, which promote each other and proceed in turn. Firstly, SEI membrane decomposition releases heat to heat the battery, which promotes the reaction between negative electrode and solvent to release more heat, leading to the reaction between negative electrode and binder, solvent decomposition. Then the positive electrode starts thermal decomposition reaction, releasing a large amount of heat and gas, and finally leads to the combustion or explosion of the battery.

3. Short circuit, needle-punching and impact have almost the same harm to lithium-ion batteries. When short circuit occurs, the current generates a lot of heat through the instantaneous of the battery, heating the battery, raising the temperature of the battery to the decomposition temperature of the positive electrode, which leads to the thermal decomposition of the positive electrode out of control; when the needling speed is very fast, local short circuit is caused at the needle point and a lot of heat is generated, which makes the temperature inside the battery rise to the decomposition temperature of the positive electrode; when the lithium ion battery is impacted, the electric energy is out of control. Overvoltage loss on the pole generates heat, which promotes the reaction between solvent and negative pole. The heat emitted further heats the battery, and promotes the thermal decomposition reaction of positive pole, which leads to heat loss.