Research Progress on Modification of Cathode Materials for Lithium-ion Batteries

Since Yoshino first invented the C/LiCoO2 battery system in 1983, rechargeable lithium-ion secondary batteries have undergone nearly 40 years of development. They are widely used in mobile electronic devices, new energy vehicles and other fields due to their portability, safety and long cycle life. In recent years, cathode materials such as binary and ternary layered oxides and LiFePO4 have gradually become prevalent for research in the field of energy storage. However, the disadvantages of the above cathode materials are also obvious, such as poor reversibility, degradation during the reaction process, low energy density and low electrical conductivity, which have become problems that cannot be ignored. The modification methods of three types of commonly used cathode materials are introduced, the main problems faced by each type of cathode materials are discussed, and the research progress of the corresponding modification methods are summarized. Starting from the different crystal structures of the three types of cathode materials, the basic principles of various modification methods are described, and the effects of various modification methods on the crystal structures and electrochemical properties of the materials are clarified. The development history of lithium-ion batteries is summarized accordingly, and the current research status of modification methods at home and abroad is investigated. Through the comparison of these modification methods, the modification means of popular domestic cathode materials in recent years are analyzed and the future research directions are prospected. The modification methods of cathode materials mainly include surface coating, anion and cation doping, material morphology and structure design, and electrolyte composition other than the material itself. Surface coating is the most commonly used method in the modification process. The coating layer usually acts as a physical barrier to reduce the side reaction between the active material and the electrolyte, but too thick a coating layer will also affect the diffusion rate of lithium ions. Cationic doping can be divided into lithium-stop doping and transition metal positions depending on the substitution position, both of them can improve the structural stability of the material. In contrast, anion doping is used to improve the cyclic stability by inhibiting the release of oxygen from the material. Material morphology and structure design generally include material nanosizing, special morphology design and so on. The fundamental purpose is to shorten the diffusion path of lithium ions and increase the specific surface area of the material to improve the multiplier performance. In addition, the selection of suitable electrolyte and additives can also indirectly modify the cathode material, which is in essence the regulation of the electrode/electrolyte interface. At present, there are more research and development of lithium-rich layered materials and polymer phosphates in China, and surface coating and bulk phase doping are more mature and widely used modification methods. With the gradual popularization of new energy vehicles, the cost of batteries and their range at high mileage have become issues that cannot be overlooked. Further optimization of the preparation process and improvement of the energy density of the battery is still an urgent problem to be solved. In the future, all-solid electrolyte and other different battery systems need to be further explored. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.