What are the main reasons for lithium battery capacity degradation?

　　The positive and negative electrodes, electrolyte and separator are important components of lithium ion battery. The positive and negative electrodes of lithium ion battery have lithium intercalation and stripping reaction respectively, and the lithium intercalation amount of the positive and negative electrodes becomes the main factor affecting the capacity of lithium ion battery. Therefore, it is necessary to maintain the balance of the positive and negative electrode capacities of lithium ion batteries to ensure that the batteries have the best performance.

　　Generally speaking, the electrolyte solution consisting of organic solvent and electrolyte (lithium salt) is commonly used in lithium batteries. The electrolyte solution should have sufficient conductivity, stability, and be compatible with the electrode. For the diaphragm, its performance is the main factor determining the internal resistance and interface structure of the battery, and has a direct impact on the change of battery capacity attenuation. If the quality and performance of the diaphragm are superior, the capacity and comprehensive performance of the lithium ion battery will be significantly improved. In general, the diaphragm in the battery is mainly used to separate the positive pole and negative pole of the battery, so as to avoid short circuit of the battery caused by contact between the positive and negative poles. At the same time, it can also release electrolyte ions to fully play the role of the battery.

　　Chemical reactions in lithium ion batteries not only include redox reactions in the process of lithium ion insertion and removal, but also include side reactions such as the production and destruction of the SEI film on the anode surface, the decomposition of electrolyte, and the structural change and dissolution of active materials. These side reactions are the reasons for the capacity degradation of lithium ion batteries.

　　It is inevitable that capacity degradation and loss occur during battery cycle. Therefore, in order to improve battery capacity and performance, scholars in various fields at home and abroad have fully studied the mechanism of lithium battery capacity loss. At present, it is known that the main factors causing the capacity degradation of lithium ion batteries include the formation of SEI passive films on the positive and negative electrode surfaces, the deposition of lithium metal, the dissolution of electrode active materials, the occurrence of redox reaction or side reaction of the cathode and anode, structural changes and phase changes. At present, the change of lithium ion battery capacity attenuation and its causes are still in the process of continuous research.

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