What are the possible reasons for the capacity degradation of lithium batteries?

1. Self-discharge of the battery Self-discharge refers to the natural loss of electric capacity when the battery is not in use. The capacity loss caused by the self-discharge of lithium batteries can be 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 recovered during charging, while the irreversible capacity loss is the opposite. The positive and negative electrodes may have side reactions with the electrolyte (microbattery reaction) in the charged state, and lithium ion intercalation and deintercalation will occur. The lithium ions inserted and extracted are only related to the lithium ions in the electrolyte, and the capacity of the positive and negative electrodes is therefore unbalanced, and this part of the capacity loss cannot be recovered during charging. For example, the reaction between the positive electrode and the solvent: LiyMn2O4+xLi++xe→Liy+xMn2O4 Solvent molecules (such as PC) are oxidized on the surface of the conductive material carbon black or the current collector as the negative electrode of the microbattery: xPC→xPC-radical+xe; negative electrode The reduction reaction with solute LiPF6 PF5+xe→PF5-x Lithium carbide in the charged state is used as the negative electrode of the microbattery to remove lithium ions and be oxidized: LiyC6→Liy-xC6+xLi++xe2. Electrode instability includes electrode instability. The structure changes during the charge and discharge/cycle process, and the positive electrode dissolves due to structural defects. 3. The corrosion of the current collector. Copper and aluminum are the most commonly used materials for the negative and positive current collectors, respectively. The current collector corrosion is related to the electrolyte. In LiPF6-EC/DMC electrolyte, the voltage is 4.2V (vs.Li/Li+) to corrode aluminum foil. Aluminum foil is easier to be on the surface whether in the air or in the electrolyte. The oxide film is formed. At the same time, general corrosion and local corrosion (such as pitting) and poor adhesion on the surface of the current collector will increase the electrode reaction resistance and increase the internal resistance of the battery, resulting in a loss of capacity and a decrease in discharge efficiency. The copper current collector corrodes during use to form a layer of insulating corrosion product film. As a result, the internal resistance of the battery increases, and the discharge efficiency decreases during the cycle, resulting in capacity loss. In addition, there are overcharge and overdischarge during use, and analysis of electrolyte will cause the loss of lithium battery capacity. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.