Lithium battery self-discharge method

Lithium battery self-discharge refers to the phenomenon that the voltage of the battery drops during the open circuit. In the lithium manganate, lithium cobaltate, and ternary material electrodes, the self-discharge phenomenon of the lithium battery is unavoidable.

Lithium-ion battery self-discharge is divided into two types according to the capacity loss: the capacity loss is reversible, which means that the capacity can be recovered after recharging; the capacity loss is irreversible, indicating that the capacity cannot be recovered. The factors affecting the degree of self-discharge are: the preparation process of the cathode and the battery, the nature and concentration of the electrolyte, the storage temperature of the battery and the storage time, wherein the dependence on temperature is relatively large.

The self-discharge of lithium-ion batteries is small, and most of the capacity loss can be recovered. The reason behind this phenomenon is analyzed by taking lithium manganate as an example.

In terms of mechanism, the self-discharge of a fully charged lithium battery is caused by the decomposition reaction of the electrolyte and the initial insertion reaction of lithium, the former being irreversible and the latter being reversible.

Furthermore, the reason why the insertion and deintercalation of lithium in the positive and negative electrodes can be recovered is because both electrodes self-discharge at the same rate, thereby implying a capacity balance mechanism, but after long-term self-discharge, the capacity balance of the two electrodes will be It is gradually broken, and there is a danger that lithium will precipitate in the carbon negative electrode during the charging process, resulting in unrecoverable capacity.

The self-discharge rate can be expressed by the self-discharge rate of the lithium battery, but, this self-discharge rate is uncertain. In terms of mechanism, mainly controlled by the oxidation rate of the electrolyte solvent, the solvent oxidation mainly occurs on the surface of the carbon black, and the low surface area carbon black can control the self-discharge rate, and for the lithium manganate battery, the surface area of the active material is reduced, It is also important to delay the oxidation of the solvent on the current collector. The above is the source of different self-discharge rates during the preparation of the lithium battery.

Lithium battery self-discharge also has external factors. First, the influence of storage time, as described above, the longer the time, the capacity balance between the positive and negative electrodes of the lithium battery is gradually broken and deepened, and the decomposition reaction of the electrolyte also accumulates some irreversible capacity loss. Therefore the longer the storage time the larger the self-discharge rate.

The self-discharge rate of lithium-ion batteries is negligible compared to other types of batteries, which is determined by the structure of the lithium battery. Therefore, the expression for the self-discharge rate of a lithium battery is generally calculated as a capacity loss of one month. Generally, the monthly self-discharge rate of a lithium battery at room temperature is 3%, but it may accelerate if it is not paying attention to the environment. For example, the self-discharge rate is 10% at a high temperature of 55 ° C or higher, which is more than 3 times at room temperature. Although the capacity caused by self-discharge is mostly recoverable, the self-discharge rate at such a high temperature is still striking, and the long-term unsuitable temperature environment naturally has a great influence on the ultimate life of the lithium battery.

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