Li4P2O7 modified high performance Li3V2(PO4)3 cathode material

Abstract

Li₃V₂(PO₄)₃ was prepared from a stoichiometric and a non-stoichiometric set of precursors. The non-stoichiometric preparation led to particles coated with a thin layer (<5 nm) of Li₄P₂O₇ and Li₃PO₄ (G-LVPO), as verified through high resolution transmission electron microscopy and slow scan X-ray diffraction. The stoichiometric material was bare (B-LVPO), i.e. no film was present, as confirmed by the same techniques. Amorphous and crystalline Li₃V₂(PO₄)₃ will co-exist when the synthesis temperature ranges from 700 °C to below 900 °C. The Li₃V₂(PO₄)₃ phase will completely crystallize and particles grow bigger than 300 nm when the synthesis temperature reaches to or higher than 900 °C. Cyclic voltammetry plots of B-LVPO and G-LVPO show that they undergo the same phase transitions between 3.0 V and 4.3 V and preserve a good structural stability over cycled in the range from 3.0 V to 4.8 V. G-LVPO has a smaller ohmic/charge transfer resistance compared with B-LVPO, which enables a better rate capability and cycling ability of G-LVPO than B-LVPO. In this report we were able to determine that the non-stoichiometric chemistry leads to a coating of Li₄P₂O₇ and Li₃PO₄ on the Li₃V₂(PO₄)₃ and that the coating appears to improve the rate capability and the cycling ability of the material.