Tuning the Fe/P Ratio to Suppress Li/Fe Antisite Defects and Achieve High-Rate Performance in Fe-Deficient LiFePO4/C

Carbon coated Fe-deficient LiFexPO4 (x = 0.95, 0.96, 0.97, 0.98, 0.99) cathodes were produced by a combined co-precipitation and carbothermal reduction routes. The effect of the Fe/P atomic ratio on the crystal structure Li/Fe antisite defect, and electrochemical performance of non-stoichiometric cathode materials was investigated. X-ray diffraction patterns and Rietveld refinements reveal that, even when the Fe/P ratio is less than 1.0, the cathode preferentially forms a LiFePO4 phase containing iron vacancies rather than a mixture of LiFePO4 and Li3PO4. Because Li-site vacancies and structural integrity induced by the Fe/P ratio exert opposite effects, the highest capacity is obtained at an Fe/P ratio of 0.97.