Synthesis and electrochemical properties of Ti4+ doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li3 − xFe2 − xTix(PO4)3/C (x = 0–0.4) cathodes designed with Fe doped by Ti was studied. Both Li3Fe2(PO4)3/C (x = 0) and Li2.8Fe1.8Ti0.2(PO4)3/C (x = 0.2) possess two plateau potentials of Fe3+/Fe2+ couple (around 2.8 V and 2.7 V vs. Li+/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li2.8Fe1.8Ti0.2(PO4)3/C has higher reversibility and better capacity retention than that of the undoped Li3Fe2(PO4)3/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.

► Li3 − xFe2 − xTix(PO4)3/C composite cathodes were prepared by ball-milling method. Ti-doping can improve the electrochemical property of Li3Fe2(PO4)3.
► The optimized doping level was found to be x = 0.2.
► The second phase of LiTi2(PO4)3 will emerge if the doping level higher than 0.2.