Lithium batteries are widely used in electric vehicles, and battery fire incidents are common in electric vehicles. So what factors can cause lithium batteries to fire? Here are five death science experiments to explore.
1 foreign body puncture
There is a diaphragm between positive and negative electrodes in lithium battery. The main function of the diaphragm is to prevent positive and negative contacts and allow ions to transfer through the diaphragm. Once the diaphragm is damaged by foreign body puncture, if the foreign body is a metal material, it will directly lead to the short circuit of the positive and negative electrodes through the metal foreign body; if the foreign body is non-metal, the diaphragm is destroyed in the puncture process, resulting in the direct short circuit caused by the contact between the positive and negative electrodes.
For electric vehicles using lithium batteries, if they are punctured by foreign bodies raised on the ground during driving, the situation described above will occur, causing short-circuit heating in damaged lithium batteries, gradually affecting other lithium batteries, eventually causing the whole battery package to fire.
2. External impact
External impact will lead to damage to the internal structure or shell of lithium batteries. In serious cases, the electrodes of lithium batteries will be exposed to the air. Because the lithium-embedded negative of lithium batteries has strong reducibility, which is close to the nature of lithium in metallic state, once contacted with the air, it will heat and smoke, and if not controlled in time, it will ignite.
For electric vehicles, external shocks are very common, such as bottom knocking of battery pack and accident collision, which will impact lithium batteries. Once the internal structure of lithium batteries is destroyed by external shocks, it will easily lead to short circuit of electrodes or exposure of electrodes. The damaged batteries will burn and ignite other batteries, and eventually spread the fire to other batteries Normal battery.
3 Internal Short Circuit
In the use of lithium batteries, lithium dendrite will be produced due to environmental temperature, electrode characteristics and other factors. Lithium dendrite accumulation will destroy the diaphragm and lead to short circuit of positive and negative electrodes. Heat accumulation will cause the self-ignition of lithium batteries. In addition to the internal short circuit caused by lithium dendrite formation in the use process, defects in the diaphragm and burrs in collecting fluid will also be broken. Bad diaphragm leads to internal short circuit.
For electric vehicles, the internal short circuit of lithium batteries will cause the spontaneous combustion of electric vehicles. At present, a large part of the spontaneous combustion of electric vehicles in the market is caused by the internal short circuit of lithium batteries. This situation is generally without warning. When signs of spontaneous combustion are found, it is impossible to prevent the deterioration of the situation.
4. Overcharge and Overdischarge
Overcharging of lithium batteries will lead to the heating of electrolyte and the decomposition of gas, which will form pressure inside sealed batteries, leading to the expansion of lithium batteries. If the diaphragm ruptures, the contact between positive and negative electrodes will lead to short circuit and fire. Similarly, high-power external overdischarge can also cause internal heating and expansion of the battery, and similar damage process as overcharge can lead to fire.
5 Internal water intake
Lithium is a very active metal in the negative pole of lithium batteries. When water comes into contact, it will undergo intense chemical reaction. Water will be decomposed into hydrogen and a lot of heat will be released to cause combustion. The internal water intake of lithium batteries will lead to catastrophic consequences.
For electric vehicles, if water enters the battery pack, the lithium battery shell will be corroded gradually due to electrochemical reaction. Once the shell is corroded until the electrodes are exposed, the electrodes will immediately react violently with water, and eventually ignite the whole battery pack.
Through the above five small experiments, we know the cause of lithium battery fire, and know that lithium battery fire is extremely difficult to control. Therefore, once smoke, fire and other symptoms are found in the use of electric vehicles, it is necessary to escape at the first time, not because of petty negligence!