Synthesis mechanism of LiNiVO4 by wet chemical method and mixed valence of nickel and vanadium

The single phase LiNiVO₄ has been successfully synthesized by adopting a new mild liquid route with oxalic acid as both complexant and precipitant, and this method is named the CPG method. The products were obtained by sintering the dry gel precursor which was prepared by the CPG method at 200–850 °C for 2–10 h in air. The products were tested by XRD, XPS, ESR and TGA-DTA, and the results indicate that the single phase LiNiVO₄ could be obtained at 450°C for 2–3 h in air and LiNiVO₄ was still steady at 850 °C for 10 h. The valence analyses show that in LiNiVO₄ the valence of lithium is +1, both nickel and vanadium have the mixed valence, namely +2, +3 for nickel and +4, +5 for vanadium respectively. The LiNiVO₄ can be expressed as LiNi³⁺ _x Ni²⁺ _1-x V⁴⁺ _x V⁵⁺ _1-x O₄ (0⩽x<1). The pyrolysis mechanism of the dry gel is also discussed.