How Should We Choose Charger
Self-discharge of intelligent rechargeable batteries refers to the phenomenon of voltage drop during the open-circuit static process. In lithium manganate, lithium cobalt oxide and ternary material electrodes, self-discharge of intelligent rechargeable batteries is inevitable.
The self-discharge of intelligent rechargeable batteries can be divided into two kinds according to whether the capacity loss is reversible or not: the capacity loss is reversible, which means that the capacity can be restored after recharging; the capacity loss is irreversible, which means that the capacity can not be restored. The factors affecting the degree of self-discharge include the preparation process of cathode and battery, the nature and concentration of electrolyte, storage temperature and storage time of battery, among which the dependence on temperature is greater.
Smart rechargeable batteries have small self-discharge, and most of the capacity loss can be recovered. The reasons behind this phenomenon are analyzed with lithium manganate as an example.
In terms of mechanism, the self-discharge of charged smart rechargeable batteries is caused by the decomposition reaction of electrolyte and the initial intercalation reaction of lithium. The former is irreversible, while the latter is reversible.
Furthermore, the reason why the insertion and de-insertion of lithium in positive and negative electrodes can be restored is that both electrodes self-discharge at the same rate, which implies the mechanism of capacity balance. However, after long-term self-discharge, the capacity balance of the two electrodes will gradually be broken down, and lithium will precipitate in the process of charging. Danger, resulting in capacity unrecoverable.
The self-discharge rate can be expressed by the self-discharge rate of intelligent rechargeable batteries, but the self-discharge rate is uncertain. In mechanism, it is mainly controlled by the oxidation rate of electrolyte solvent. Solvent oxidation mainly occurs on the surface of carbon black. Low surface area carbon black can control the self-discharge rate. For manganese acid smart rechargeable batteries, it is also important to reduce the surface area of active material and delay the oxidation of solvent on the collector. These are the causes of different self-discharge rates in the preparation of intelligent rechargeable batteries.
The self-discharge of intelligent rechargeable batteries 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 positive and negative electrodes of intelligent rechargeable batteries will be gradually broken and deepened, and the electrolyte decomposition reaction will accumulate some irreversible capacity losses. Therefore, the longer the storage time is, the higher the self-discharge rate will be.
The self-discharge rate of smart rechargeable batteries is insignificant compared with other types of batteries, which is determined by the structure of smart rechargeable batteries. Therefore, the self-discharge rate of intelligent rechargeable batteries is generally calculated by one month capacity loss. Usually, the monthly self-discharge rate of smart rechargeable batteries is 3% at room temperature, but it is possible to accelerate without paying attention to the environment. For example, the self-discharge rate of smart rechargeable batteries at high temperatures above 55 C is 10%, which is more than three 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 astonishing. Long-term under unsuitable temperature environment, the ultimate life of intelligent rechargeable batteries will naturally be greatly affected.