Types of lithium battery explosions.

Types of lithium battery explosions.

The types of battery cell explosions can be classified into three categories: external short circuit, internal short circuit, and overcharging. The external refers to the exterior 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 the electronic components fail to cut off the circuit, high heat is generated inside the battery cell, causing some electrolyte to vaporize and expanding the battery casing. When the internal temperature of the battery reaches 135 degrees Celsius, high-quality separator paper will close the pores, terminate or almost terminate the electrochemical reaction, cause a sudden drop in current, and gradually lower the temperature, thereby avoiding explosion. However, if the pore closure rate is too poor, or if the pores do not close at all, the separator paper will cause the battery temperature to continue to rise, more electrolyte to vaporize, and eventually rupture the battery shell, even raising the battery temperature to the point where the material burns and explodes. Internal short circuits are mainly caused by burrs on copper foil and aluminum foil penetrating the diaphragm, or dendritic crystals of lithium atoms penetrating the diaphragm.

These small needle like metals can cause micro short circuits. Due to the thin needle having a certain resistance value, the current may not be very high. Copper and aluminum foil burrs are caused during the production process, and the observable phenomenon is that the battery leaks too quickly, which can mostly be detected by battery cell factories or assembly plants. 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 due to burrs is not high. This statement can be supported by statistics, as there are often defective batteries with low voltage shortly after charging in various battery cell factories, but explosion incidents rarely occur. Therefore, explosions caused by internal short circuits are mainly due to overcharging.

Because after overcharging, needle shaped lithium metal crystals are everywhere on the electrode, piercing points are everywhere, and micro short circuits are occurring everywhere. Therefore, the battery temperature will gradually increase, and eventually the high temperature will release the electrolyte gas. In this situation, whether it is the high temperature causing the material to burn and explode, or the shell being first stretched and causing air to enter and undergo intense oxidation with lithium metal, both are the end of the explosion. However, the explosion caused by internal short circuit due to overcharging may not necessarily occur at the time of charging. It is possible that when the battery temperature is not high enough for the materials to burn and the gas produced is not enough to break the battery casing, consumers may terminate charging and take their phones out. At this point, the heat generated by numerous micro short circuits slowly increases 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 their phone, they find it very hot, and when they throw it away, it explodes.