What is overcharge and overdischarge? What are the hazards to lithium batteries?

       It is often heard from lithium battery manufacturers that lithium batteries cannot be overcharged or overdischarged, otherwise the battery will be damaged. So what is overcharge and overdischarge? What are the hazards to lithium batteries?

       Overcharge:

       Overcharge means that when the lithium ion battery is overcharged, the charging voltage exceeds the set voltage, for example, the battery rated voltage is 3.7V, and the full-charge voltage is 4.2±0.05V. That is, the high voltage is 4.25V. If it exceeds 4.25V, it is called overcharge. What harm does overcharge have to the battery?

       During overcharge, the battery voltage rises rapidly with the increase of polarization, which will cause irreversible changes in the structure of the positive electrode active material and the decomposition of the electrolyte, which will generate a large amount of gas and release a large amount of heat, causing the battery temperature and internal pressure to increase sharply. The internal diaphragm Melting or shrinking will cause the positive and negative electrode materials to contact and short-circuit, and there will be hidden dangers such as explosion and combustion.

       Overdischarge:

       Overdischarge refers to the discharge when the voltage reaches the rated voltage and continues to discharge. For example, the rated discharge voltage of a ternary lithium battery is 3.2V. If the discharge voltage is lower than 3.2V, the discharge continues to be overdischarge. What harm does over-discharge have to the battery?

       After the battery has discharged the internally stored power, after the voltage reaches a certain value, continuing to discharge will cause overdischarge. Overdischarge of the battery may bring catastrophic consequences to the battery, especially high current overdischarge or repeated overdischarge. Bigger. Generally speaking, over-discharge will increase the internal pressure of the battery, destroy the reversibility of the positive and negative active materials, decompose the electrolyte, deposit lithium on the negative electrode, and increase the resistance. Even if it is charged, it can only partially recover, and the capacity will be significantly attenuated. .

       How to avoid overcharging or overdischarging the battery?

       One: Use the lithium battery special protection board (BMS) to work with the battery. The protection board can protect the battery from overcharging or overdischarging. The smart version can also set the charging voltage and discharging voltage, which can better protect the battery.

       Two: Use the supporting lithium battery charger instead of fast charging.

       Three: When the battery voltage reaches the voltage set by the protection board, the protection board will cut off the power to protect the battery, but the lithium battery will fall back and the voltage will rise, which will be a little higher than the voltage set by the protection board. It can no longer be used at this time. Repeated use will cause irreversible damage to the battery.