What is battery self-discharge and electrode instability？

Self-discharge refers to the natural loss of electrical capacity when the battery is not in use. The capacity loss caused by self-discharge of lithium-ion battery is divided into two situations: one is reversible capacity loss; the other is irreversible capacity loss. Reversible capacity loss means that the lost capacity can be restored during charging, while the irreversible capacity loss is the opposite. For example, the lithium manganese oxide positive electrode and the solvent will interact with the microbattery to produce self-discharge and cause irreversible capacity loss. The degree of self-discharge is affected by factors such as the cathode material, the manufacturing process of the battery, the nature of the electrolyte, temperature and time. For example, the self-discharge rate is mainly controlled by the oxidation rate of the solvent, so the stability of the solvent affects the storage life of the battery. If the negative electrode is in a fully charged state and the positive electrode self-discharges, the Rechargeable Alkaline battery content balance will be destroyed, which will result in permanent capacity loss. During long-term or frequent self-discharge, lithium may be deposited on the carbon, increasing the capacity imbalance between the two stages. Pistoia et al. believed that the oxidation products of self-discharge block the micropores on the electrode material, which makes the insertion and extraction of lithium difficult, increases the internal resistance and reduces the discharge efficiency, resulting in irreversible capacity loss.
Electrode instability
The positive active material will oxidize and decompose the electrolyte in the charged state, causing capacity loss. In addition, the factors affecting the dissolution of the positive electrode material include the structural defects of the positive electrode active material, the excessively high charging potential and the content of carbon black in the positive electrode material. Among them, the most important factor is the change potential of the electrode structure during the charge and discharge cycle.
Lithium cobalt oxide is a hexagonal crystal in a fully charged state, and a new phase of monoclinic crystal is formed after 50% of the theoretical capacity is discharged. The lithium nickel oxide involves rhombohedral and monoclinic changes during the charge-discharge cycle. LiyNiO2 usually 0.3<y<="" span="">Cycle within the range. There are two different structural changes in lithium manganese oxide during the charge and discharge process: one is the phase change that occurs when the stoichiometry is unchanged; the other is the phase change that occurs when the amount of lithium insertion and extraction changes during the charge and discharge process. When the LiCoO2 lithium-ion battery charging voltage exceeds 4.2V, the capacity loss is directly related to the cobalt content detected at the negative electrode, and the higher the charging cut-off current voltage, the greater the cobalt dissolution rate. In addition, the capacity loss (or cobalt dissolution) is related to the heat treatment temperature of the synthetic active material.