The cathode materials of lithium-ion batteries are usually composed of active compounds of lithium, while the negative electrodes are carbon with special molecular structure. The main components of the common cathode materials are licoo2/LiFePO4, etc. When charging, the potential added to the battery poles forces the positive compounds to release lithium ions and embed the anode molecules into the carbon with a lamellar structure. During discharge, lithium ions precipitate from the carbon of the lamellar structure and recombine with the compounds of the positive electrode. The movement of lithium ions produces an electric current.

Although the chemical reaction principle is very simple, in the actual industrial production, there are much more practical problems to be considered: the positive material needs additives to maintain the activity of multiple charging and discharge. the negative material needs to be designed at the molecular structure level to accommodate more lithium ions; the electrolyte filled between the positive and negative electrodes not only needs to maintain stability, but also needs to have good conductivity and reduce the internal resistance of the battery.

Although lithium-ion batteries rarely have the memory effect of Ni-CD batteries, the principle of memory effect is crystallization, which rarely occurs in lithium-ion batteries. However, the capacity of lithium-ion battery will still decrease after many times of charge and discharge, and the reasons are complex and diverse. It is mainly the change of the positive and negative electrode material itself. from the molecular level, the hole structure of the positive and negative electrode containing lithium ion will gradually collapse and block; from a chemical point of view, it is the active passivation of the positive and negative electrode material and the occurrence of side reactions to form other stable compounds. In physics, the cathode material will gradually peel off, which ultimately reduces the number of lithium ions in the battery that can move freely in the process of charge and discharge.

Overcharging and overdischarge will cause permanent damage to the positive and negative electrodes of lithium-ion battery. from the molecular level, it can be understood intuitively that excessive discharge will lead to the excessive release of lithium ions from negative carbon, resulting in the collapse of its lamellar structure. overcharging will force too many lithium ions into the negative carbon structure, so that some of them can no longer be released. This is why lithium-ion batteries are usually equipped with charge and discharge control circuits.
Unsuitable temperature will trigger other chemical reactions in lithium-ion batteries to form compounds that we do not want to see, so there are protective temperature-controlled diaphragms or electrolyte additives between the positive and negative electrodes of many lithium-ion batteries. When the battery temperature rises to a certain level, the hole of the composite membrane is closed or the electrolyte is denatured, the internal resistance of the battery increases until the circuit is broken, and the battery no longer heats up, which ensures that the charging temperature of the battery is normal.

The charging process of lithium-ion battery is divided into two stages, the constant current fast charging stage (when the battery indicator is yellow) and the constant voltage current decreasing stage (the battery indicator is flashing green. In the constant current fast charging stage, the battery voltage gradually increases to the standard voltage of the battery, and then it is transferred to the constant voltage stage under the control chip, the voltage no longer rises to ensure that it will not be overcharged, and the current gradually decreases to 0 with the increase of the battery charge, and the charging is finally completed.

The discharge curve of lithium-ion battery will change after many times of use. If the chip does not have the opportunity to read a complete discharge curve again, the calculated amount of electricity is not accurate. So we need a deep charge to calibrate the battery chip. But you don't have to make sure that every time you turn off the power and recharge.
You can do a deep charge and discharge under the control of the protection circuit for a period of time to correct the battery statistics, but this will not increase the actual capacity of your battery.

Batteries that have not been used for a long time should be placed in a cool place to reduce the speed of their own passivation reaction.

The protection circuit is also unable to monitor the self-discharge of the battery. Batteries that have not been used for a long time should be charged with a certain amount of electricity to prevent the damage of excessive self-discharge caused by excessive self-discharge in storage.

Because the electric memory effect of lithium-ion battery is negligible, the damage caused by halfway charging is not great, and what it fears most is excessive discharge (full discharge). Often the result of excessive low discharge of lithium-ion batteries can only be scrapped ahead of time, and lithium-ion batteries do not have to wait until 0% to recharge.