Improved cycle life of Fe-substituted LiCoPO4

Fe-substituted LiCoPO4 exhibits greatly improved cycle life relative to LiCoPO4. Whereas, pure LiCoPO4 loses more than half of its discharge capacity at the 10th cycle, the Fe-substituted LiCoPO4 retains about 100% of its discharge capacity at the 10th cycle and about 80% of its capacity at the 500th cycle. It is suggested that improved cycle life results from Fe3+ substitution on the Li and Co sites. The partial substitution of Li+ by Fe3+ and Co2+ by Fe2+ and Fe3+ was evidenced from Rietveld analysis of X-ray powder diffraction data, infrared spectroscopy, X-ray photoelectron spectroscopy and Mössbauer spectroscopy. The majority of the Fe3+ substitutes at the Co2+ site. The composition of Fe-substituted LiCoPO4 is Li0.92Co0.8Fe2+0.12Fe3+0.08PO4 for a sample of starting composition LiCo0.8Fe0.2PO4.