Introduce the failure mechanism of lithium-ion batteries

In the standard cycle life test, the discharge capacity should not be less than 90% of the initial capacity when the number of cycles reaches 500. Or the discharge capacity should not be less than 80% of the initial capacity when the number of cycles reaches 1000. If the capacity drops sharply within the standard cycle range, it is a capacity attenuation failure. The root cause of battery capacity decay failure is the failure of materials, and it is closely related to objective factors such as battery manufacturing process and battery use environment. From a material point of view, the main reasons for the failure are the structural failure of the positive electrode material, the transitional growth of SEI on the negative electrode surface, the separation and deterioration of the electrolyte, the corrosion of the current collector, and the trace impurities of the system. Structural failure of positive electrode material: The structural failure of positive electrode material includes crushing of positive electrode material particles, irreversible phase transition, material disorder, etc. During the charging and discharging process, the structure of LiMn2O4 will be distorted due to the Jahn-Teller effect, and the particles may even be broken, causing electrical contact between the particles to fail. The LiMn1.5Ni0.5O4 material will undergo a tetragonal-cubic phase transition during the charge and discharge process. The LiCoO2 material will enter the Li layer due to the transition of Li during the charge and discharge process, causing the layered structure to become chaotic and restrict Its capacity to play. Anode material failure: The failure of the graphite electrode mainly occurs on the graphite surface. The graphite surface reacts with the electrolyte to process the solid electrolyte interface phase (SEI). If excessive growth will lead to a decrease in the lithium content in the battery's internal system, the result is a capacity degradation. The failure of silicon anode materials is mainly due to the cycle performance problems caused by their huge volume expansion. Electrolyte failure: LiPF6 has poor stability and is easy to decompose to reduce the amount of migrating Li+ in the electrolyte. It also easily reacts with traces in the electrolyte to generate HF, causing corrosion inside the battery. Poor air-tightness causes the electrolyte to deteriorate, and the viscosity and chromaticity of the electrolyte change, which ultimately leads to a sharp decline in ion transmission performance. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Explain the difference between series and parallel lithium-ion batteries