Causes of lithium battery explosion
As the application range of lithium batteries becomes wider and wider, explosions of lithium batteries occur from time to time. To ensure the safety of the battery system, the reasons for the battery explosion must be analyzed more carefully. The reasons for the explosion of lithium batteries are probably as follows:
1. The pole pieces of the internal lithium battery are highly polarized, causing an internal short circuit of the lithium battery to cause an explosion;
2. The pole piece of the lithium battery absorbs water and reacts with the electrolyte. The gas drum causes an internal short circuit of the lithium battery and causes an explosion;
3. The quality and performance of the electrolyte itself cause the internal short circuit of the lithium battery to cause an explosion;
4. The amount of liquid injected cannot meet the technological requirements when injecting liquid;
5. In the assembly process, laser welding has poor sealing performance, and air leakage when measuring air leakage;
6. Dust and pole piece dust are likely to cause micro short circuits first;
7. The positive and negative plates are thicker than the process range, making it difficult to enter the shell;
8. The problem of liquid injection sealing, poor sealing performance of the steel ball leads to air bulging;
9. The shell wall is too thick in the incoming shell material, and the shell deformation affects the thickness;
10. Explosion caused by external short circuit;
11. Excessive ambient temperature outside is also the main cause of explosion.
Lithium battery explosion type
Explosion type analysis The types of battery cell explosion can be summarized into three types: external short circuit, internal short circuit, and overcharge. The outside here refers to the outside of the battery cell, including short circuits caused by poor internal insulation design of the battery pack. When a short circuit occurs on the outside of the cell and the electronic components fail to cut off the circuit, high heat will be generated inside the cell, which will cause part of the electrolyte to vaporize and expand the battery shell. When the internal temperature of the battery reaches 135 degrees Celsius, a good quality diaphragm paper will close the pores, the electrochemical reaction will be terminated or almost terminated, the current will drop sharply, and the temperature will slowly drop, thus avoiding an explosion. However, the pore closure rate is too poor, or the pores are not closed at all, the battery temperature will continue to rise, more electrolyte will vaporize, and finally the battery shell will be broken, and the battery temperature will even be increased. The material burns and explodes. The internal short circuit is mainly caused by the burrs of the copper foil and aluminum foil piercing the diaphragm, or the dendritic crystals of lithium atoms piercing the diaphragm.
These tiny needle-like metals can cause micro short circuits. Since the needle is very thin and has a certain resistance value, the current is not necessarily large. The copper and aluminum foil burrs are caused by the production process. The observable phenomenon is that the battery leaks too fast, most of which can be screened by the battery cell factory or the assembly factory. Moreover, due to the small burrs, they are sometimes burned, causing the battery to return to normal. Therefore, the probability of explosion caused by burr micro-short circuit is not high. This statement can be seen from the fact that there are often bad batteries with low voltage shortly after charging in various battery cell factories, but there are few explosions, which is supported by statistics. Therefore, the explosion caused by an internal short circuit is mainly caused by overcharging.
Because, after overcharging, there are needle-like lithium metal crystals everywhere on the pole piece, the piercing points are everywhere, and micro short circuits are occurring everywhere. Therefore, the battery temperature will gradually increase, and finally the high temperature will cause the electrolyte to gas. In this case, whether the temperature is too high to cause the material to burn and explode, or the shell is first broken, causing the air to enter and oxidize the lithium metal, it is an explosion. However, the explosion caused by an internal short circuit caused by overcharging does not necessarily occur at the time of charging. It is possible that when the battery temperature is not high enough to burn the material and the gas generated is not enough to break the battery casing, the consumer will stop charging and take the mobile phone out. At this time, the heat generated by numerous micro-short circuits slowly raises the temperature of the battery, and it explodes after a period of time. The common description of consumers is that when they pick up the phone, they find that the phone is very hot and explode after throwing it away.
Based on the above types of explosions, we can focus on three aspects of explosion protection: prevention of overcharge, prevention of external short circuits, and improvement of cell safety. Among them, overcharge prevention and external short circuit prevention belong to electronic protection, which has a greater relationship with battery system design and battery assembly. The focus of battery cell safety improvement is chemical and mechanical protection, which has a greater relationship with battery cell manufacturers.
