The battery cell is the main component of a battery, and its explosion types can be classified into three types: external short circuit, internal short circuit, and overcharge. The external refers to the external part of the battery cell, including short circuits caused by poor insulation design inside the battery pack. When a short circuit occurs outside the battery cell and electronic components fail to cut off the circuit, high heat is generated inside the battery cell, causing some electrolyte to vaporize and causing the battery casing to become larger. When the internal temperature of the battery reaches 135 degrees Celsius, a high-quality diaphragm paper will close the fine pores, terminate or almost terminate the electrochemical reaction, cause a sudden drop in current, and the temperature will slowly decrease, thereby avoiding the occurrence of an explosion. However, if the closing rate of the pores is too poor, or if the pores do not close at all, the diaphragm paper will cause the battery temperature to continue to rise, more electrolyte will vaporize, the battery shell will be stretched, and even the battery temperature will be raised to cause the material to burn and explode. Internal short circuits are mainly caused by burrs on copper and aluminum foils penetrating the diaphragm, or dendritic crystals of lithium atoms penetrating the diaphragm. These small needle shaped metals can cause micro short circuits. Due to the fine needle having a certain resistance value, the current may not necessarily be very high. Copper aluminum foil burrs are caused during the production process, and the observed phenomenon is that the battery leakage is too fast, which can be mostly detected by the battery cell factory or assembly plant through screening. Moreover, due to the small burrs, they can sometimes be burned off, causing the battery to return to normal. Therefore, the probability of explosion caused by micro short circuits in burrs is not high. This statement can be seen from the fact that there are often faulty batteries with low voltage shortly after charging in various battery manufacturers, but explosion incidents are rare, which is statistically supported. Therefore, the explosion caused by internal short circuits is mainly due to overcharging. Because after overcharging, needle shaped lithium metal crystals are everywhere on the electrode, puncture points are everywhere, and micro short circuits are occurring everywhere. Therefore, the temperature of the battery will gradually increase, and the high temperature will release the electrolyte gas. In this situation, whether the material burns and explodes due to excessive temperature, or the shell is first stretched out, causing air to enter and undergo intense oxidation with lithium metal, it is the end of the explosion. However, the explosion caused by internal short circuits caused by overcharging does not necessarily occur at the time of charging. It is possible that when the battery temperature is not high enough for the material to burn and the gas produced is not enough to break through the battery casing, consumers will terminate charging and take their phones out. At this point, the heat generated by numerous micro short circuits slowly raises the temperature of the battery, and after a period of time, an explosion occurs. The common description among consumers is that when they pick up a phone, they find it very hot, and after throwing it away, it explodes. Based on the types of explosions mentioned above, we can focus on preventing overcharging, external short circuits, and improving the safety of battery cells. Overcharge prevention and external short circuit prevention belong to electronic protection and are closely related to battery system design and battery assembly. The key to improving the safety of battery cells is chemical and mechanical protection, which is closely related to battery cell manufacturers.

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