Optimized carbon-coated LiFePO4 cathode material for lithium-ion batteries

Lithium iron phosphate (LiFePO4) cathode material has been synthesized by a solid-state reaction. The XRD patterns of the samples show that the single-phase LiFePO4 compounds can be obtained in our experimental conditions. According to Popa theory, using the result from Rietveld refinement, the shape and the size of crystallite can be obtained. The result shows that the use of carbon gel in precursors do not change the structure of the crystal, but it can inhibit the particle growth and restrain the anisotropy growth of the grain at a lower temperature. At a higher temperature, carbon-coated LiFePO4 shows an anisotropy growth, i.e. growth rate along (1 0 0) crystal plane is more rapid than that of (1 1 1) crystal plane. In our experimental conditions, a spherical carbon-coated LiFePO4 can be synthesized successfully at 650 °C. The electrochemical testing indicated that the spherical carbon-coated LiFePO4 had the excellent performance. Its initial specific capacities were 156.7 mAh g−1 under the rate of C/10. At the 50th cycle, the reversible specific capacities were found to approach 151.2 mAh g−1 (the ratio of 96.5% of initial capacity).