Synthesis and electrochemical properties of Ge-doped Li3V2(PO4)3/C cathode materials for lithium-ion batteries

Ge-doped electrode materials Li3V2-xGex(PO4)3/C (x = 0, 0.01, 0.05, and 0.09) were synthesized by the sol-gel method. The morphologies and microstructures were characterized by transmission electron microscopy and X-ray diffraction, respectively. The valence states of the elements and electrochemical performance of the electrode materials were evaluated by X-ray photoelectron spectroscopy and constant current tests, respectively. The results indicated that an appropriate Ge doping level significantly improved the electrochemical properties of the Li3V2(PO4)3/C cathode. The Li3V1.99Ge0.01(PO4)3/C sample exhibited the best electrochemical performance, with a specific discharge capacity of 137.2 mAh g−1 at 0.2 C and 118.4 mAh g−1 at 5 C in the potential range of 2-4.3 V. After the charge-discharge process at different rates, the initial discharge capacity retention was 97.0%. Thus, the material is shown to exhibit excellent rate capability and stability.