Why do rechargeable lithium batteries need protections?
The negative electrode of li-ion/li-po batteries consists of, mainly, carbon or graphite that can store or release Li ions. Once there’s an over discharge voltage, the Li ions turn to be Li metals and deposit on the carbon or graphite surfaces. Because the Li metal is very active, it can burn by any flush or other reasons. The electrolyte contains flammable organic solvent. Therefore, once the used charger goes wrong and there is an overcharge voltage existing, the voltage goes above 4.7V, the Li-ion batteries will be overheated and then to be burned. In order to prevent deep discharge that leads to shorten the cycle life of the battery, the Li-ion batteries need an over discharge protection.
