"With the development of mobile communication equipment and electric cars, there is an increasing demand for high capacity lithium-ion batteries. It is difficult for the present commercialized lithium-ion power batteries to meet the requirement of one charge to travel above 500 km, because of low discharge capacity, like lithium iron phosphate and ternary cathode material, possessing the discharge capacity lower than 180 mAh/g. Therefore, the specific capacity of cathode materials has become a bottleneck to increase the energy density of lithium-ion batteries. Lithium-rich cathode materials with large specific capacity (≥250 mAh/g), high discharge voltage (3.8 V), and high theory energy density (900 Wh/kg) are thought as ideal cathode material of power batteries for electric cars in the future, so, it is of great realistic significance to study the lithium-rich cathode materials with high specific capacity. This paper reviews the development of cathode materials for lithium-ion batteries as well as the situation of recent commercial cathode materials with low specific capacity. Structures and electrochemical properties of lithium-rich cathode materials as a new next-generation higher capacity are summarized, and the discharge mechanism and the latest progress in modifications are presented. Moreover, some problems related with lithium-rich materials for high energy-density lithium-ion batteries are presented, followed by the corresponding ideas and approaches of solution.

Contents
1 Introduction
2 Structural research of lithium-rich materials
3 Investigation on electrochemical behaviors of lithium-rich materials
3.1 Interpretation on the first charge/discharge
3.2 Interpretation on capacity and voltage fade
4 Modified research on lithium-rich materials
4.1 Surface coating
4.2 Bulk doping
4.3 Nanosizing
4.4 Hierarchical structure
4.5 Concentration-gradient distribution
4.6 Layered/Spinel heterostructure
4.7 Other methods
5 Conclusion