Polycrystalline layered-type cathode materials are usually in the form of spherical secondary particles consisting of an aggregate of primary particles. The surface of polycrystalline cathode particles contains features in the form of pits and valleys, leading to a high surface area. As the parasitic reactions with electrolyte occur at cathode surfaces, it is important to reduce the surface area in order to obtain long cycle life. Here, we present a study of using a mechanofusion method to reduce the surface area and improve the cycling performance of LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622).

Figure 1(a) shows an SEM image of a pristine NMC622 particle. Primary particles can be seen clearly on the surface of a pristine NMC622 particle, resulting in a rough surface. Figure 1(b) shows an SEM image of an NMC622 particle processed with the mechanofusion method. After the mechanofusion process, the secondary particle size does not change. However, it is apparent that the surface has been smoothed compared to pristine NMC622. Figure 1(c) shows the voltage curve of materials processed using the mechanofusion method for varying times. Figure 1(d) shows the capacity retention rate of all the materials. NMC622 processed with mechanofusion method has better capacity retention than pristine NMC622, which is ascribed to its reduced surface area, resulting in reduced parasitic reactions with electrolyte.