Studies of Composite Cathode Material LiFePO4–Li3V2(PO4)3 and It’s Precursor FeVO4·xH2O

Abstract

Abstract As both iron and vanadium sources, the spherical amorphous FeVO4·xH2O powders are synthesized through an aqueous precipitation method by using Fe(NO3)3, NH4VO3, and ammonia water as starting materials. The effects of pH value of precursor solution on the Fe/V molar ratio is studied, it is found that when the pH is 4, the Fe/V molar ration is 1.004, it is close to 1. The FeVO4·xH2O powders are preheat treated at 600 °C for 12 h in air to obtain triclinic FeVO4. The FeVO4 powders are homogeneously mixed with Li2CO3, NH4H2PO4, and oxalic acid with stoichiometric ratio, and then sinter at 750 °C for 12 h in argon atmosphere to obtain LiFePO4–Li3V2(PO4)3 composite material. The structural properties, particle morphology, and electrochemical performance of composite cathode material LiFePO4–Li3V2(PO4)3 were studied. The FeVO4 not only plays as the main reactant to form LiFePO4 and Li3V2(PO4)3, but also as the dopants doping LiFePO4–Li3V2(PO4)3. The LiFePO4–Li3V2(PO4)3 composite cathode shows good electrochemical performance, and its discharge capacity is about 138.7 mA h g−1 at 1 C rate after 100 cycles, which retains 93.3% of it’s theoretical capacity (148.6 mA h g−1) for composite cathode material LiFePO4–Li3V2(PO4)3 in the voltage range of 2.5–4.5 V.