Abstract:γ-LiV2O5/VO2 composites were synthesized through thermal lithiation reaction of mixed valence (+4, +5) vanadium oxides by lithium bromide. The phase evolution, morphology and discharge behavior at 500 ℃ were investigated by thermal gravimeter/differential thermal analysis (TG/DTA), X-ray diffraction(XRD), scanning electron microscopy(SEM) and specific surface analysis(BET). The mixed vanadium oxides are obtained from the pyrolytic decomposition of ammonium metavanadate, with V6O13 as main phase. Results show that the lithiation reaction begins at about 258 ℃, with γ-LiV2O5 and VO2(B) as the product. VO2(B) can transit to VO2(R) in the range of 400−500 ℃, following by grain growth and crystalline development with the increase of temperature and roasting time. The ratio of γ-LiV2O5 to VO2 can be modified by the additive content of lithium bromide. A lattice shearing model about the nucleation and growth of LixV2O5 and VO2(B) inside mixed valence (+4, +5) vanadium oxides (e.g. V6O13, V3O7) is speculated, which is relative to oxygen-/vacancy-diffusion and structural evolution inspired by lithium-insertion. The open-circuit voltage of 2.6 V is observed in the single cell of Li-B/LiCl-KCl/(γ-LiV2O5/VO2) at 500 ℃, and the specific capacities of 146 and 167 mA∙h/g (cut-off voltage 1.4 V) are measured for the positive material at 100 mA/cm2 and 200 mA/cm2, respectively.

Key words: thermal cell; γ-LiV2O5/VO2 composite material; lithiation