Lithium battery has been developed for decades since published. Most mobile phones currently on the market also have built-in lithium batteries. Despite decades of development, lithium batteries still can not guarantee 100% safety, and even explode in some specific environments. Lithium Ion batteries are subject to Thermal Runaway, and this occurs when the separator blocking the flow of electrons in the battery fails. According to the statistics of the Fire Department of the Ministry of the interior in Taiwan, there have been 32 lithium battery fires throughout the country from January to May in 2020. The main reason for the lithium battery fire is that the heat is out of control. From energy storage power system to mobile power supply, the main cause of battery fire is thermal runaway.
The fire and explosion of lithium battery has the following characteristics:
- The negative electrode capacity of lithium battery is insufficient
When the capacity of the negative part of the positive part of the lithium battery is insufficient, the lithium atoms generated during charging can not be inserted into the interlayer structure of the negative graphite, and will precipitate on the surface of the negative electrode to form crystals. Long term crystallization in lithium battery will lead to short circuit, when the cell discharges rapidly, a lot of heat will be generated and the diaphragm will be burned. High temperature will decompose the electrolyte into gas. When the pressure is too high, the cell will explode.
- High moisture content
When charging, the water can react with lithium to produce lithium oxide, which will cause the capacity loss of the cell. It is easy to overcharge the cell and generate gas. The decomposition voltage of water is low, so it is easy to decompose and generate gas when charging. When this series of generated gas will increase the internal pressure of the cell, and when the shell of the cell cannot bear it, the cell will explode.
- Internal short circuit
The short circuit of the internal cell will cause large current discharge, generate a lot of heat, burn the diaphragm, and cause greater short circuit phenomenon, which will decompose the electrolyte into gas. If the internal pressure is too high, the cell will explode.
- Overcharge of lithium battery
When the cell is overcharged, the excessive discharge of lithium in the positive electrode will change the structure of the positive electrode, and the excessive discharge of lithium is easy to be unable to be inserted into the negative electrode, and also easy to cause lithium evolution on the surface of the negative electrode. Moreover, when the voltage reaches more than 4.5V, the electrolyte will decompose and produce a large amount of gas. All of which could cause an explosion of lithium batteries.
- External short circuit
The external short circuit may be caused by the wrong connection of the positive and negative electrodes. Due to the external short circuit, the discharge current of the battery is very high, which will make the cell heat up. The high temperature will shrink or completely damage the diaphragm inside the cell, causing the internal short circuit and explosion.
The safety problems of lithium batteries do exist. In addition to the manufacturers must recognize and prevent the possible safety risks caused by the use of lithium batteries, the general consumers also have the responsibility. They must face up to the danger of lithium batteries and understand the combustion characteristics of lithium batteries in order to avoid accidents.