Abstract:

With the rapid development of technologies related to the power supply and energy storage in electric vehicles, Ni-rich layered oxides have become the most preferred cathode materials for application in power batteries owing to their high capacity and low cost. However, these layered oxides suffer from inferior cycling performance and poor rate capability, seriously impeding their practical application. Ni-rich single-crystalline can effectively mitigate the generation of particle cracking and improve the cycling stability of Ni-rich cathode materials; however, the severe preparation conditions of high nickel single crystals limit their development. Herein, polycrystalline Ni-rich LiNi_0.9Co_0.05Mn_0.05O₂ (NCM-PC) and single-crystalline LiNi_0.9Co_0.05Mn_0.05O₂ (NCM-SC) were prepared via coprecipitation combined with the high-temperature solid-state and molten-salt methods, respectively. The crystallographic structure, microstructure, electrochemical properties and Li⁺ diffusion kinetics of two cathode materials were systematically studied via scanning electron microscopy, x-ray diffractometry, constant current intermittent titration technique, and electrochemical tests. The results of this study demonstrate that NCM-PC possesses a relatively high lithium-ion diffusion coefficient, resulting in excellent rate performance. For instance, NCM-PC could deliver a discharge capacity of 164 mAh/g at 10 C. Although NCM-PC exhibits a low discharge capacity at a high C-rate, it exhibits an outstanding cycling performance with capacity retention of ～89 % after 100 cycles at 3 C. This study provides a theoretical basis for optimizing the particle size and electrochemical performance of single-crystalline/polycrystalline NCM materials having high-Ni content (≥90 %).

Key words: lithium-ion battery, Ni-rich cathode, single-crystalline, polycrystalline, rate capability