Electrochemical and Magnetic Studies of Li-Deficient Li1-xCo1-xFexPO4 Olivine Cathode Compounds

Abstract

Li-deficient olivine compounds, Li1-xCo1-xFexPO4 (x < 0.15), were prepared by calcination of the sol-gel derived precursors in ambient atmosphere. They were almost single phase at x < 0.10 but some impurity phases were found at x > 0.10. The lattice parameters changed continuously with an increase in the Fe substitution. Their variation in the range of x < 0.10 roughly obeyed Vergard's law. From the 57Fe Mössbauer spectrum at room temperature, it was shown that the introduced Fe took a trivalent high-spin state in the olivine lattice. The temperature-dependent magnetic susceptibility exhibited that the Fe incorporation enhanced the antiferromagnetic ordering: the Neel temperature shifted higher. Furthermore, the electrochemical performances, such as cycling stability and rate capability, were improved significantly with an appropriate substitution (about 10%) with Fe3+. Consequently, the Fe3+ incorporated compounds with Li deficiency as the charge compensation are thought to be good candidates as high-voltage cathode material, which may enhance the energy density of Li ion battery.