Synthesis And Electrochemical Performance Of Layered Li-rich Cathode Materials For Li-ion Batteries

The development of new-generation of green energy has become an important strategic choice for sustainable development of human society. Lithium ion batteries (LIBs) as a new green energy storage device, have advantages of high operating voltage, high energy density, non-pollution, long cycle life and so on, which have promising prospect in electric vehicles and energy storage. The overall performance of LIBs depends primarily on the cathode materials, so the design of high-performance cathode materials is the key to the development of new-generation high-energy LIBs. Compared with other cathode materials (such as LiCoO2, LiFePO4, LiMn2O4, etc.), lithium-rich layered cathode material xLi2MnO3-(1-x)LiMO2 (M= Ni, Co, Mn) can deliver a discharge capacity of more than 250 mAh g-1, which makes it a promising candidate of cathode material for future LIBs. In this research work, nano-structured and hierarchical micro/nano-structured Li-rich layered oxides were adopted to improve its poor rate capability and cycle stability.Ethylene glycol and PVP were used to synthesize nano-structured Li-rich material Li1.2Mn0.56Ni0.16Co0.08O2. The structure, morphology and electrochemical performances of the as-prepared samples with and without PVP were extensively investigated. Li1.2Mn0.56Ni0.16Co0.08O2 sample synthesized with PVP has uniform distribution of primary particles with sizes of 50-100 nm and is well crystallized. Discharge capacities of 286.1,266.4,234.1,209.7,184.9,151.7 and 123.3 mAh g=1 are obtained at current densities of 20,40,100,200,400,1000 and 2000 mA g=1 between 2.0 and 4.8 V, respectively. Nano particles have shorter lithium-ion diffusion pathways and larger surface areas, which improve the utilization of active material and enhance the rate capability.A novel hierarchical micro/nano lithium-rich cathode material Li1.2Mn0.54Ni0.18Co0.08O2 was synthesized via a facile solvothermal method combined with a calcination process. The as-prepared sample with a peanut-like micro-structure is composed of primary particles with sizes of 100-300 nm, and has high crystallinity and well-formed layered structure. As a cathode material for Li-ion batteries, it delivers a discharge capacity of 229.9 mAh g-1 at a current density of 200 mA g-1 between 2.0 and 4.8 V with a high capacity retention of 94.2% after 100 cycles. High reversible discharge capacities of 198.3,167.5 and 145 mAh g-1 are obtained at 400, 1000 and 2000 mA g-1, respectively. The excellent electrochemical performances are attributed to the reduced Li-ion diffusion path length and good structural stability of the hierarchical structure.