At present, lithium batteries are used more and more widely in various digital devices such as notebooks, digital cameras, and digital video cameras. In addition, they also have broad prospects in automobiles, mobile base stations, and energy storage power stations. In this case, the use of batteries no longer appears alone as in mobile phones, but more in the form of series or parallel battery packs.
The capacity and life of the battery pack are not only related to each single battery, but also related to the consistency between each battery. Poor consistency will greatly affect the performance of the battery pack.
The consistency of self-discharge is an important part of the influencing factors. A battery with inconsistent self-discharge will have a large difference in SOC after a period of storage, which will greatly affect its capacity and safety.
The main reasons for self-discharge are: internal electronic leakage caused by partial electronic conduction of the electrolyte or other internal short circuits; due to poor insulation of the battery sealing ring or gasket or insufficient resistance between the external lead shell (external conductor, humidity) The external electron leakage caused by the electrode/electrolyte reaction, such as the corrosion of the anode or the reduction of the cathode due to the electrolyte and impurities; the partial decomposition of the electrode active material; the electrode caused by the decomposition products (insoluble matter and adsorbed gas) Passivation; mechanical wear of the electrode or increased resistance between the electrode and the current collector.
Self-discharge will cause the capacity to decrease during the storage process: the car cannot be started after parking for too long; everything is normal before the battery is put into storage, and low voltage or even zero voltage is found when the battery is shipped; the car GPS is placed on the car in summer and used for a while I feel that the power or usage time is obviously insufficient, and even the battery swells.
The self-discharge of metal impurities causes the diaphragm pore size to be blocked, and even pierces the diaphragm to cause a local short circuit, which endangers the safety of the battery. The large difference in SOC can easily lead to overcharge and overdischarge of the battery.
Due to the inconsistent self-discharge of the batteries, the SOC of the batteries in the battery pack is different after storage, and the battery performance is reduced. Customers can often find performance degradation problems after they get a battery pack that has been stored for a period of time. When the SOC difference reaches about 20%, the combined battery capacity is only 60% to 70% remaining.
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