Electrochemical Performance Of Lithium-rich Layered Oxide Cathode Materials For Li-ion Batteries

As one of the most important chemical-electrical energy conversion devices, the rechargeable lithium-ion batteries (LIBs) have been widely used in the area of power, illumination, communication and portable electronic devices for their high energy density, high working-voltage, long circle-life and high safety performance. However, fast-growing energy consumption leads to a higher requirement for LIBs: higher energy density, longer cyclic life and more reliable security, especially in electric vehicles and electricity storage systems. So we have to actively develop new systems and new materials. After research and development of many years, the reversible capacity of anode materials far exceeds that of cathodes. In addition, cathodes account for about 30%-40% of overall costs. Hence the performances of cathode materials determine the overall performances of the batteries and we must focus on the cathodes in order to develop high-performance lithium ion batteries. Lithium-rich layered transition metal oxides are considered as one of the most promising candidates for the next generation cathode materials due to their high energy density, high power density and high thermal stability. In this paper, we mainly focused on the structures and electrochemical properties of lithium-rich layered Li2RuO3-LiCoO2 composite and Li3NbO4-NiO composite, and some interesting results were obtained as follows:1. A layer-structured Li2RuO3-LiCoO2 composite was synthesized by the solid-state reaction method. In the as-prepared composite, Li2RuO3 component not only serves as the electrochemical active phase providing large reversible capacity, but also improves the structural stability of layered LiCoO2 at high potential. Electrochemical measurements show the composite has high reversible specific capacity and good capacity retention. Particularly, the initial discharge specific capacity can reach 240 mAh/g at the current density of 0.13 C between 2.0V and 4.5 V. It also exhibits an excellent cycling stability with capacity retention of 75% after 50 cycles. The present work suggests choosing appropriate transition metal M and M’for Li2MO3-LiM’O2 composite should be an efficient strategy for designing new cathode materials.2. A series of Li3NbO4-NiO solid solution were also prepared by the solid-state reaction method. Electrochemical measurements show the composite has high reversible specific capacity, especially for samples with high Nb content. The initial discharge specific capacity can reach 340 mAh/g at a moderate current density, in a wide range of charge and discharge cut-off voltages. Large reversible capacity is actually attributable to the reversible redox of Ni, coupled with redox reactions of oxide ions. In a word, it should be an efficient strategy to use oxide ion redox for desiging positive electrode materials for LIBs.