The positive and negative electrodes of a lithium-ion battery undergo intercalation and deintercalation reactions of lithium, respectively, and the amount of intercalation of lithium in the positive and negative electrodes becomes the main factor affecting the capacity of the lithium-ion battery. Therefore, it is necessary to maintain the balance of the positive and negative capacity of lithium-ion batteries to ensure the best performance of the battery.
Generally speaking, an electrolyte solution composed of an organic solvent and an electrolyte (lithium salt) is commonly used in lithium batteries. The electrolyte solution should have sufficient conductivity, stability, and compatibility with electrodes. For the separator, its performance is the main factor that determines the internal resistance and interface structure of the battery, and has a direct impact on the change of the battery capacity attenuation. If the quality and performance of the separator are superior, the capacity and overall performance of the lithium-ion battery will be significantly improved.
Under normal circumstances, the separator mainly plays the role of separating the positive electrode and the negative electrode of the battery in the battery, avoiding the short circuit of the battery caused by the contact between the positive and negative electrodes, and at the same time, it can release the electrolyte ions to give full play to the battery function.
The chemical reactions in Li-ion batteries include not only redox reactions during Li-ion intercalation and de-intercalation, but also side reactions such as the production and destruction of SEI films on the negative electrode surface, the decomposition of electrolytes, and the structural changes and dissolution of active materials. These side reactions are the reasons for the capacity fading of Li-ion batteries.
Capacity fading and loss during battery cycling are inevitable phenomena. 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 that cause the capacity decay of lithium-ion batteries include the formation of SEI passivation film on the surface of positive and negative electrodes, the deposition of metallic lithium, the dissolution of electrode active materials, the occurrence of cathode and anode redox reactions or side reactions, structural changes and phase changes, etc. . At present, the capacity fading changes of lithium-ion batteries and their causes are still in the process of continuous research.
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