Synthesis and electrochemical performance of Sn-doped Li3V2(PO4)3/C cathode material for lithium ion battery by microwave solid-state technique

Li3V2−xSnx(PO4)3/C cathode materials with uniform and fine particle sizes were successfully and fast synthesized by a microwave solid-state synthesis method. X-ray diffraction patterns demonstrated that the appropriate addition of Sn did not destroy the lattice structure of Li3V2(PO4)3/C, but decreased the unit cell volume. X-ray photoelectron spectroscopy analysis demonstrated that the main chemical state of V in the Li3V1.95Sn0.05(PO4)3/C composite is +3 valence, while the chemical state of Sn in the Li3V1.95Sn0.05(PO4)3/C is +4 valence. Scanning electron microscope analysis illustrated that the addition of Sn slightly affected the morphology of samples. As the cathode materials for Li-ion batteries, Li3V2−xSnx(PO4)3/C (x ⩽ 0.10) exhibited higher discharge capacity and better cycle stability than the pure one. At a discharge rate of 0.5 C in the potential range of 2.5–4.5 V at room temperature, the initial discharge capacity of Li3V1.95Sn0.05(PO4)3/C was 136 mA h/g. The low charge-transfer resistances and large lithium ion diffusion coefficients confirmed that Sn-doped Li3V2(PO4)3/C samples possessed better electronic conductivity and lithium ion mobility. These improved electrochemical performances can be attributed to the appropriate amount of Sn doping in Li3V2(PO4)3/C system by enhancing structural stability and electrical conductivity. The present study also demonstrates that the microwave processing is a fast, simple and useful method for the fabrication of Li3V2(PO4)3/C crystals.