Nanocomposite LiFePO4·Li3V2(PO4)3/C synthesized by freeze-drying assisted sol-gel method and its magnetic and electrochemical properties

Abstract

Nano-sized LiFePO4·Li3V2(PO4)3/C was synthesized via a sol-gel route combining with freeze-drying. X-ray diffraction results show that this composite mainly consists of olivine LiFePO4 and monoclinic Li3V2(PO4)3 phases with small amounts of V-doped LiFePO4 and Fe-doped Li3V2(PO4)3. The magnetic properties of LiFePO4·Li3V2(PO4)3/C are significantly different from LiFePO4/C. Trace quantities of ferromagnetic impurities and Fe2P are verified in LiFePO4/C and LiFePO4·Li3V2(PO4)3/C by magnetic tests, respectively. LiFe-PO4·Li3V2(PO4)3/C possesses relatively better rate capacities and cyclic stabilities, especially at high charge-discharge rates. The initial discharge capacities are 136.4 and 130.0 mA h g−1, and the capacity retentions are more than 98% after 100 cycles at 2 C and 5 C, respectively, remarkably better than those of LiFePO4/C. The excellent electrochemical performances are ascribed to the mutual doping of V3+ and Fe2+, complementary advantages of LiFePO4 and Li3V2(PO4)3 phases, the residual high-ordered carbon and Fe2P with outstanding electric conductivity in the nanocomposite.