R6 Carbon battery.Latest research on the failure mechanism of lithium battery NCM111 materials

　　It has not yet been determined whether ternary materials are suitable for use in electric vehicles, but one thing is certain, that is, ternary materials have high capacity, are easy to synthesize, and are cathode materials with excellent performance. The biggest problem currently faced by ternary materials is how to ensure a good cycle life of the material while exerting a high capacity. Current research has found that the factors that affect the cycle life of ternary materials include the following:

　　1) Reconstruction of surface crystal structure during cycling.

　　2) Secondary particle rupture due to anisotropic volume expansion during cycling. These problems can be solved by modifying the microstructure of the secondary particles, surface coating treatment, and optimizing the charge and discharge procedures.

　　The study found that the particle-particle connection structure inside the secondary particles of the material will cause a local increase in current density, thereby generating great stress, thus affecting the cycle performance of the material. At the same time, there are also inconsistent charging states between various parts inside the particles, which will affect the electrochemical performance of the electrode. In the research on NCA material LiNi0.8Co0.15Al0.05O2, it was found that during the formation process, there is a lithium insertion process in the core-shell structure. It is generally believed that under a small current density and sufficient standing time, such an uneven The diffusion process can disappear. But the latest research findings cast doubt on this. Generally speaking, the state of charge SOC of a battery refers to the state of charge of the entire battery. William E. Gent of Stanford University and others have achieved the observation of local SOC of the electrode through technical means, which is very important for studying the inhomogeneity inside the electrode. significance. The study found that even after 170 hours of standing, high Li+ inhomogeneity was still observed in the NCM secondary particles. The difference in Li concentration inside a secondary particle with a diameter of 1-3 μm can reach 10%, which is consistent with There is a big difference between the state we expected. William E. Gent believes that due to the random arrangement of primary particles inside secondary particles, the stress generated is highly anisotropic, resulting in differences in Li concentration within the particles. This also leads to a big problem. The local SOC value of the particles is too high, which will lead to local overcharging and accelerate the failure of this part, thus leading to a decrease in the overall capacity of the material.

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