What are the harms of overcharging and overdischarging to batteries?

What are the harms of overcharging and overdischarging to batteries?

Overcharge
The so-called overcharging, as the name suggests, refers to overcharging, that is, continuing to charge the battery after it is fully charged.
 
After being fully charged and continuing to charge to a certain extent, the gas produced by the decomposition of the electrolyte in lithium-ion batteries can cause the battery to expand and even smoke. In this way, the battery cannot function properly. Just like a balloon, if it continues to inflate after being fully inflated, the balloon will eventually burst.
 
Some customers, for the sake of the beauty of their products or to meet the requirements of product mold design, often only purchase battery cells and design their own protective plates, which can also easily cause overcharging. On the one hand, due to their low level of battery expertise, outdated experimental equipment, and differences in the designed overcharge protection parameters; On the other hand, due to the different quality of battery cells produced by different battery cell manufacturers and the different lithium materials used, if they cannot judge and always use the same process to design overcharge protection parameters, it is also easy to make errors and lead to overcharging.
 
Of course, overcharging once or twice does not cause much damage to the battery, and the user experience is not deep. However, over time and with more overcharging times, the battery will undergo a qualitative change due to changes in quantity, until it cannot be charged or discharged. The result can be imagined.


over-discharge
The so-called overdischarge refers to the situation where the battery discharges its internal stored power, and the voltage drops to a certain value before continuing to discharge, resulting in overdischarge. The discharge cut-off voltage is usually determined based on the discharge current, which is the critical voltage value to determine whether there is over discharge. For a 3.7V lithium battery, the 0.2C-2C discharge is generally set at 3.0V, and for discharges above 3C, such as 5C or 10C discharge, it is set at 2.4V.
 
Overdischarging of batteries often brings catastrophic consequences, especially high current overdischarging or repeated overdischarging, which has a greater impact on the battery's electrical performance. This is like a person losing three to five hundred milliliters of blood at once, which does not affect their physical health, but once the blood loss is too much, their normal bodily functions cannot be maintained, and to a certain extent, they will die. For batteries, overdischarging can cause an increase in internal pressure and damage the reversible function of positive and negative active materials. Even with charging remedies, it is difficult to fully recover. Naturally, the capacity significantly decreases, and when it decays to a certain extent, the battery "dies" and there is no way to revive it.
 
In order to avoid excessive negative consequences, we should set targeted protection parameters based on the characteristics of the battery itself in the early stage, and strictly follow the battery "usage regulations" in the user manual to ensure quality and quantity in the later stage of use. It is best to leave some "residual power" for the battery, just like "leaving a line of work for future meetings", laying a "foundation" for recharging, just like doing things, starting from scratch is difficult after all. We have always emphasized that rechargeable batteries are an applied science, and their use is particularly important. Once used properly, they will obediently obey your commands, fulfill their duties, and serve you until you are satisfied. Especially for highly active lithium-ion batteries, they should be taken care of carefully. Otherwise, they will abandon you to a difficult to tame horse, making you laugh and cry.