Progress of LiMnyFe1−yPO4 Cathode Materials: From Mechanisms, Defects, Modification Methods to Applications

Abstract

Cathode materials play a vital role in determining the electrochemical performance of a lithium-ion battery. They have a direct impact on the energy density, cycle life, rate performance, and safety of the battery. LiMn_yFe_1−yPO₄ (0 < y < 1, LMFP) inherits the advantages of high safety and low cost of LiFePO₄ (LFP) materials and also makes up for the shortcomings of the low energy density of LFP materials to a certain extent. It is considered to be a promising cathode material. However, LMFP exhibits extremely low ionic and electronic conductivity. Due to the Jahn–Teller effect, high Mn content will cause serious Mn dissolution and other problems, which seriously hinder the large-scale application of LMFP. This paper provides a comprehensive review of the structural characteristics, reaction mechanisms, and methods to enhance the electrical conductivity of LMFP cathode materials. It primarily focuses on the effects of particle size optimization, morphology control, surface coating, ion doping, and mixing with other layered cathode materials to improve the electrical conductivity of LMFP and their underlying mechanisms. These modification methods can improve the electron/ion transmission path between material particles and the conductivity of LMFP to a certain extent. However, these methods alone make it difficult to solve the problem of poor conductivity of LMFP cathode materials. To further improve the comprehensive electrochemical performance of LMFP materials, this paper provides a summary of the current research progress and presents future research ideas and development directions for LMFP. The strategy of combined modification by heteroatom-doped carbon material coating, short b-axis, morphology control, and ion doping is proposed, and the main development direction and research ideas of LMFP in the future are pointed out.