What harm does overcharge and overdischarge do to the battery?

The so-called overcharge, as the name implies, is overcharged, that is, after the battery is fully charged, continue to charge it.

If the battery is charged to a certain extent after being fully charged, the gas generated by the decomposition of electrolyte in the lithium-ion battery will cause the battery to expand and even smoke. In this way, the battery will not work normally. Just like a balloon, it will burst sooner or later if it continues to be filled with gas.

Some customers, for the beauty of their products or to meet the requirements of product mold design, often only purchase batteries and design their own protection plates, which is also easy to cause overcharge. On the one hand, because their battery professional level is not high, the experimental equipment is backward, and the designed overcharge protection parameters are different; On the other hand, because the quality of batteries produced by different battery manufacturers is different, the lithium materials used are also different. If they can't judge, they always use the same process to design overcharge protection parameters, which is also prone to errors and lead to overcharge.

Of course, overcharging once or twice does little harm to the battery and the user experience is not deep, but after a long time and more overcharging times, the battery will deteriorate due to quantitative change until it can't be charged or discharged, and the result can be imagined.