Li-ion battery charging and overcharging knowledge explanation

At present, the most important way to charge lithium-ion batteries is the voltage-limiting and current-limiting method. The initial constant current (CC) charging has the strongest battery acceptance. The most important is the endothermic reaction, but when the temperature is too low, the activity of the material will decrease, and it may enter the constant current stage ahead of time, so it is low in winter in the north. Preheating the battery before charging can improve the charging effect. As the charging process continues, the use of polarization is strengthened, the temperature rise is intensified, along with gas evolution, the electrode overpotential increases, and the voltage rises. When the charge reaches about 70~80%, the voltage reaches the maximum charge limit voltage, and it switches to the constant voltage (CV) stage. In theory, there is no objective overcharge voltage threshold. If it is understood as gas evolution and temperature increase, it means overcharge. At the end of the constant current phase, different degrees of overcharge always occur, the temperature rise reaches 40-50 degrees Celsius, the shell deformation is easy to sense, some of the escaped gases can be recombined, and the others are the result of irreversible reactions. Loss of capacity, which can be seen as the current intensity exceeds the battery's ability to accept. In the constant voltage stage, there is a trickle charge. It takes about 30% of the time to charge 10% of the electricity. The current intensity is reduced, the gas evolution and temperature rise are no longer added, and the opposite direction changes. 2. Overcharge The above process considers the total voltage or average voltage of the battery pack. In fact, there are always those with higher cell voltage, which have entered the overcharge stage relative to other batteries in the group. During overcharging, if it occurs during the constant current stage, the voltage, temperature rise, and internal pressure continue to rise due to the high current intensity. Taking 4V lithium ion as an example, when the voltage reaches 4.5V, the temperature rises 40 degrees and the plastic case becomes hard. , The temperature rise can reach 60 degrees at 4.6V, and the shell deformation is obvious and cannot be recovered. If you continue to overcharge, the valve opens, the temperature rises continuously, and the irreversible reaction intensifies. In the constant voltage stage, the current intensity is small, and the overcharge symptoms are not as pronounced as in the constant current stage. As long as the temperature rises and the internal pressure is too high, side reactions will accompany and the battery capacity will decrease. The side reactions are inertial and develop to a certain extent. They may burn the internal materials of the battery during the charging process or in a short period of time after the end of the charging, causing the battery to be scrapped. Overcharging accelerates the degradation of battery capacity and causes battery failure, which is harmless to all benefits. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Analysis of the types of button batteries