Improved electrochemical performances of carbon-coated LiFePO4 microspheres for Li-ion battery cathode

The olivine-structured LiFePO4 have attracted a lot of interests for many advantages in lithium-ion batteries, but the low electronic conductivity and lithium ion diffusivity still limit the electrochemical performance. In order to overcome the challenge, the hydrothermal and high temperature heat treatment strategy for the synthesis of carbon-coated LiFePO4 microspheres as an example for lithium-ion batteries is reported. In this strategy, precursor composed of spherical particles and a viscous slurry was formed by hydrothermal reaction with subsequent stirring and evaporation process. After heat treatment of the precursor, LiFePO4 microspheres are formed. Carbon-coated LiFePO4 microspheres sample was prepared by using sucrose as carbon source, and the effects of structure, morphology and carbon source addition on electrochemical performance were fully studied. Results in electrochemical test demonstrate that the carbon-coated LiFePO4 showed much better performances than bare LiFePO4. The lithium-ion batteries assembled by LiFePO4/C-2 (amount of carbon source added was 15 wt%) composites as cathode material possessed large discharge capacity (ca. 116.5 mAh g(-1) at 0.1 C), good rate performance (82.8 mAh g(-1)at 2 C) and long cycling lifespan. The discharge specific capacity was maintained at 133.6 mAh g(-1) after 50 cycles with almost no attenuation, and the coulomb efficiency was close to 100%. The improved electrochemical properties may be ascribed to suitable amount of carbon source added and secondary microsphere structure.