关键词: 锂离子电池, 正极材料, LiFePO₄, 高性能

Olivine-type LiFePO₄, as an important cathode material of lithium-ion batteries, has been paying numerous attentions owing to the high theoretical capacity, good cycle stability, environmental friendliness, safety, etc.But, for bulk LiFePO₄ materials, there are some shortcomings such as the low conductivity of ca. 10^-9 S·cm^-1 and low diffusion coefficient of lithium ions.Some methods have been developed to improve its performance, including supporting, packaging, doping, and/or nanocrystallization.Carbon materials have been widely used in lithium-ion batteries as the conductive agent and modifier owing to the good conductivity, excellent electrochemical/mechanical stability, special pore structures favoring the mass transfer, low cost, and environmental friendliness.Among these, the conductivity and pore structure have a significant impact on the electrochemical performance of the cathode materials such as LiFePO₄.The carbon nanomaterials with three-dimensional hierarchical structure are paying more and more attentions because of the special pore structure.Herein, we reported the high performance of the cathode materials, LiFePO₄ supported on carbon nanocages (CNCs).CNCs are prepared using benzene as precursors and magnesium oxide as template, which have high specific surface area up to 1274 m²·g^-1, excellent electrical conductivity of 1.44 S·cm^-1, multiscale pore structure, etc.The LiFePO₄/CNCs nanocomposite was prepared following the procedure.CNCs were impregnated with the Li⁺, Fe²⁺ and PO₄^3- -containing acid solutions, the final products were obtained by sintering at 700 ℃ under the gaseous mixture of Ar and 5 vol.% H₂.The component, structure, and electrochemical performances were investigated by X-ray diffraction, transmission electron microscope, thermogravimetry, and electrochemical tests.The LiFePO₄ nanoparticles with the size of 10～25 nm were homogeneously dispersed on CNCs.The bulk conductivity of LiFePO₄/CNCs was 0.529 S·cm^-1, far higher than 2.27×10^-9 S·cm^-1 of pure LiFePO₄.The LiFePO₄/CNCs composite delivered a large discharge capacity of 163 mAh·g^-1 at a rate of 0.1 C, close to the theoretical capacity of LiFePO₄.Even at the high rates of 15 C and 30 C, the discharge capacities still reach 96 and 75 mAh·g^-1, respectively.After 200 cycles at the high rate of 15 C, the tested cell still remains a specific capacity of 92 mAh·g^-1.These results indicated that the LiFePO₄/CNCs composite as cathode material of lithium-ion batteries possessed excellent high-rate performance and cycling stability, superior to the LiFePO₄/CNTs composite.It could be ascribed to high surface area, hierarchical porous structure, and excellent electrical conductivity of CNCs support as well as the nanoscale size and high crystallinity of LiFePO₄ particles.

Key words: lithium-ion battery, cathode material, LiFePO₄, high performance