Non-Stoichiometric Carbon-Coated Lifexpo4 As Cathode Materials For High-Performance Li-Ion Batteries

A series of non-stoichiometric carbon-coated lithium iron phosphate (LiFexPO4/C) have been prepared by a solid-state reaction to study the variation of electrochemical performance at different x values. Characterized by XRD in conjunction with Rietveld refinement, Mossbauer, TEM, Raman, etc., it is indicated that the Li-O bond is elongated in the Fe-poor non-stoichiometric lithium iron phosphate with decreasing x value, while the content of Fe2P and graphitization degree of carbon layer in LiFexPO4/C samples is associated with the ratio of x. The powder electronic conductivity increases from 8.33 x 10(-2) S cm(-1) to 16.67 x 10(-2) S cm(-1) as the x value decreases from 1.04 to 0.98, which is due to a suitable amount of Fe2P and a superior graphitized carbon layer. Among different Fe/Li ratios, LiFe0.98PO4/C exhibits the highest rate capability of 163.5 mA h g(-1) at 0.1C and 93.5 mA h g(-1)1 at 20C, as well as the largest diffusion coefficient of 12.6 x 10(-14) cm(2) s(-1). It is illustrated that the synergy effect of elongated Li-O bonds, moderate Fe2P and graphitized carbon layer results in the high performance of non-stoichiometric LiFexPO4/C.