How to Choose the Right Charger?

Smart rechargeable battery self-discharge refers to the phenomenon where the battery voltage drops during open-circuit storage. This phenomenon is inevitable in smart rechargeable batteries using lithium manganate, lithium cobalt oxide, or ternary material electrodes.

Smart rechargeable battery self-discharge is classified into two types based on the reversibility of capacity loss: reversible capacity loss, where capacity can be restored through recharging; and irreversible capacity loss, where capacity cannot be recovered. Factors affecting the degree of self-discharge include the cathode and battery manufacturing process, the nature and concentration of the electrolyte, as well as the storage temperature and duration of the battery—among these, temperature has a significant dependency.

Smart rechargeable batteries exhibit low self-discharge, and most of the resulting capacity loss is reversible. Taking lithium manganate batteries as an example, we analyze the reasons behind this phenomenon.

Mechanistically, self-discharge in fully charged smart rechargeable batteries is caused by electrolyte decomposition reactions and initial lithium intercalation reactions. The former is irreversible, while the latter is reversible.

Furthermore, the recoverability of lithium intercalation and deintercalation at the positive and negative electrodes stems from self-discharge occurring at the same rate on both electrodes, implying a capacity balance mechanism. However, after prolonged self-discharge, the capacity balance between the two electrodes is gradually disrupted. This increases the risk of lithium precipitation on the carbon anode during subsequent charging, leading to irreversible capacity loss.

The rate of self-discharge can be expressed by the self-discharge rate of smart rechargeable batteries, though this rate is not fixed. Mechanistically, it is primarily controlled by the oxidation rate of the electrolyte solvent, which mainly occurs on the surface of carbon black. Using carbon black with a low specific surface area can regulate the self-discharge rate. For lithium manganate smart rechargeable batteries, reducing the surface area of active materials and delaying solvent oxidation on the current collector are also crucial—these are the root causes of varying self-discharge rates during the manufacturing of smart rechargeable batteries.

External factors also influence the self-discharge of smart rechargeable batteries. First is the effect of storage duration: as mentioned earlier, longer storage gradually disrupts and exacerbates the capacity imbalance between the positive and negative electrodes, while electrolyte decomposition accumulates irreversible capacity loss. Thus, the self-discharge rate increases with longer storage time.

Compared to other types of batteries, the self-discharge rate of smart rechargeable batteries is negligible, determined by their structural design. Therefore, the self-discharge rate of smart rechargeable batteries is typically calculated as the monthly capacity loss. Under room temperature conditions, the monthly self-discharge rate of smart rechargeable batteries is usually 3%. However, an unsuitable environment can accelerate this rate—for instance, at temperatures above 55°C, the self-discharge rate reaches 10%, more than three times that at room temperature. Although most capacity lost due to self-discharge is recoverable, the self-discharge rate at such high temperatures is alarming. Long-term exposure to inappropriate temperature environments will significantly impact the ultimate lifespan of smart rechargeable batteries.