The capacity difference of lithium-ion batteries refers to the situation where there is inconsistency in the capacity size between lithium battery cells. This is mainly because during the production and manufacturing process of lithium batteries, starting from the mixing of raw materials to the activation of product capacity, this process is quite complex, and it is difficult to ensure that the battery cells are completely consistent in all aspects, so small capacity differences may occur.
The capacity error of lithium-ion batteries objectively exists, and it can only be said that the process is constantly improved to reduce data errors. With the use of lithium-ion batteries, this capacity error will become even larger, because the internal material attenuation of the battery is different during use, resulting in different internal resistance, and the capacity size error will become larger.
This is why the consistency parameters of battery cells need to be considered when assembling or leaving the factory for battery packs. The combination of battery cells can only delay the time when the error of lithium-ion batteries increases, ultimately leading to serious capacity errors. Although it cannot avoid an increase in cell capacity error, it can delay the time of error increase. Therefore, the purpose of developing lithium-ion battery protection and balancing systems is to alleviate this error, extend battery life, and prevent and reduce the occurrence of hazards.
At present, there is a method of capacity compensation, which is to remove some of the electricity from high capacity lithium-ion batteries to compensate for the consumption of low capacity batteries. There is no problem with this method in theory, but it is very difficult to implement in practice, especially in terms of efficiency. balanced charging voltage is necessary, otherwise some lithium-ion batteries may experience undercharging during the later stages of charging. Part of lithium-ion batteries are overcharged and under charged, which affects the battery's lifespan. Overcharging can lead to danger.
It is better to do undervoltage protection than to do discharge balancing, so that any single lithium-ion battery with undervoltage can be powered off for protection to prevent the danger caused by over discharge.