As a promising candidate of the cathode materials for the next generation of high energy density lithium-ion batteries, the Li-rich transition metal oxide xLi₂MnO₃ ·(1-x)LiMO₂ (M=Ni, Co or Mn) is superior to the traditional cathode materials for its potential of achieving very high capacity of over 300mAh/g. Therefore, this type of materials is caught more and more attention in recent years. Here we give an overview of recent progress of xLi₂MnO₃ ·(1-x)LiMO₂ in recent years. The research hotspots, the crystal structure characteristics and the mechanism of initial charge and discharge, the development of various synthesis methods, as well as the improvement of the electrochemical performances for xLi₂MnO₃ ·(1-x)LiMO₂(M=Ni, Co or Mn) are commented. The future development trends of the xLi₂MnO₃ ·(1-x)LiMO₂ (M=Ni, Co or Mn) is put forward.

Contents
1 Introduction
2 Research on initial charge-discharge mechanism of Li-rich composite cathode materials
2.1 Crystal structure of Li-rich composite cathode materials
2.2 Initial charge-discharge mechanism of Li-rich composite cathode materials
3 Synthesis methods for xLi₂MnO₃·(1-x)LiMO₂
3.1 Co-precipitation method
3.2 Sol-gel method
3.3 Solid state method
3.4 Sucrose combustion method
3.5 Hydrothermal method
3.6 Low-temperature molten salt method
3.7 Other synthesis methods
4 Improvements on electrochemical properties of Li-rich composite cathode materials
4.1 Doping in the lattice
4.2 Surface coating
4.3 Doping other materials
4.4 Particle nanocrystallization and control of structures or morphologies of cathode materials
4.5 Proposing and exploration of new method
5 Conclusions and outlook