Do Lithium batteries Self Discharge – Bonnen Battery
Lithium battery self-discharge refers to the phenomenon of voltage drop in the process of open circuit standing. LiFePO4, LMO, NCM lithium battery, etc. self-discharge is inevitable. According to whether the capacity loss is reversible, lithium battery self-discharge can be divided into two types: reversible capacity loss, which means that the capacity can be recovered after recharging; capacity loss is irreversible, indicating that capacity cannot be restored.
The factors that affect the degree of self-discharge are: the manufacturing process of cathode and battery, the nature and concentration of electrolyte, the storage temperature and time of the battery, and the connection of temperature is relatively large. The self-discharge of the lithium-ion battery is small, and most of the capacity loss caused by it can be recovered. Next, take LMO as an example to analyze the reasons behind this phenomenon. In terms of mechanism, the self-discharge of a fully charged lithium battery is caused by the decomposition reaction of electrolyte and the initial embedding reaction of lithium. The former is irreversible and the latter is reversible. Furthermore, the reason why lithium can be recovered is that the two electrodes discharge at the same rate, which implies the capacity balance mechanism. However, after long-term self-discharge, the capacity balance of the two electrodes will be broken gradually, and there will be danger of lithium precipitation in the carbon negative electrode during the charging process, resulting in the capacity cannot be recovered. The speed of self-discharge can be expressed by the self-discharge rate of lithium battery, however, this self-discharge rate is uncertain. In terms of mechanism, it is mainly controlled by the oxidation rate of the electrolyte solvent. The solvent oxidation mainly occurs on the surface of carbon black. The carbon black with low surface area can control the self-discharge rate. For lithium manganese batteries, it is also important to reduce the surface area of active substances and delay the oxidation of solvent on the collector fluid. The above is the source of different self-discharge rates in the preparation of lithium batteries.
The self-discharge of the cell is also influenced by external factors. One is the effect of storage time. As mentioned above, the longer the storage time is, the capacity balance between the positive and negative electrodes of lithium battery will be gradually broken and deepened, and the decomposition reaction of electrolyte will accumulate some irreversible capacity loss. Therefore, the longer the storage time, the higher the self-discharge rate. Compared with other types of batteries, the self-discharge rate of lithium-ion batteries is negligible, which is determined by the structure of lithium-ion batteries. Therefore, the self-discharge rate of lithium batteries is generally calculated by one-month capacity loss. Generally, the monthly self-discharge rate of lithium battery at room temperature is around 3%, but it may accelerate if the environment is not noticed. For example, the self-discharge rate at a high temperature above 55 ℃ is 10%, which is more than 3 times that at room temperature. Although most of the capacity caused by self-discharge can be recovered, the self-discharge rate at high temperatures is still amazing. In the long term, under the unsuitable temperature environment, the ultimate life of lithium batteries will be a big impacted. Therefore, Bonnen Battery’s engineer suggests you take good care of storage lithium battery, try to keep in room temperature, remember to charge the battery every three months if without use for a long period.