LiFePO4 modified Li1.02(Co0.9Fe0.1)0.98PO4 cathodes with improved lithium storage properties

LiCoPO4 and Li1.02(Co0.9Fe0.1)0.98PO4 were prepared by conventional solid state reactions. The surface modification of Li1.02(Co0.9Fe0.1)0.98PO4 particulates by LiFePO4 was successfully carried out by a dry coating procedure. TEM analysis confirmed the presence of a LiFePO4 coating layer of about 20 nm on the surface of the Li1.02(Co0.9Fe0.1)0.98PO4 particles. All three cells delivered high initial discharge capacities of 122, 130 and 128 mA h g-1 for LiCoPO4, Li1.02(Co0.9Fe0.1)0.98PO4, and LiFePO4 modified Li1.02(Co0.9Fe0.1)0.98PO4, respectively. However, these cells presented quite different cycle retention rates after 20 cycles, 21, 22 and 70% for LiCoPO4, Li1.02(Co0.9Fe0.1)0.98PO4, and LiFePO4 modified Li1.02(Co0.9Fe0.1)0.98PO4, respectively. The improved cycle retention of the LiFePO4-modified Li1.02(Co0.9Fe0.1)0.98PO4 resulted from its reduced reactivity towards the electrolyte and the effective prevention of resistive layer formation on the LiCoPO4 surface during high voltage cycling.