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The influence of excessive lithium on the crystal structure, morphology, and electrochemical properties of Fe-deficient Li x FePO 4 ( x = 1.00, 1.02, 1.04, 1.05) cathode material was investigated using co-precipitation and the carbon thermal method. The X-ray diffraction pattern and Rietveld refinement results show that excessive Li + combines with the phosphate group to form Li 3 PO 4 rather than occupying the Fe site to form antisite pairs. Benefitting from the intrinsic ion conductivity of lithium phosphate, the lithium diffusion coefficient of Li x FePO 4 increases. However, the charge transfer impedance (Rct) also increases with increasing Li content due to the presence of Li 3 PO 4 , a nonconductive phase that can block the electric transfer channel. The biphasic Li x FePO 4 ( x = 1.02) compound shows the best performance. This work suggests an effective and easy way to improve the electrochemical performance by adding excessive Li, which leads to the formation of Li 3 PO 4 . [ABSTRACT FROM AUTHOR]