A comparative insight of potassium vanadates as positive electrode materials for Li batteries: influence of the long-range and local structure.

Potassium vanadates with ratio K/V = 1:3, 1:4, and 1:8, prepared by a fast and facile synthesis route, were investigated as positive electrode materials in lithium batteries. KV3O8 and K0.5V2O5 have layered structures, while K0.25V2O5 exhibits a tunnel framework isomorphic to that of β-Na0.33V2O5. The Raman spectra of KV3O8, K0.5V2O5, and K0.25V2O5 compounds are reported here for the first time, and a detailed comparative analysis distinguishes spectral patterns specific to each structural arrangement. The electrochemical performances of these potassium vanadates toward lithium insertion were investigated. The potassium-richer compound KV3O8 shows a good rechargeability in spite of a low discharge capacity of 70 mAh g(-1), while the potassium-poorer bronze K0.25V2O5 exhibits the highest specific capacity of 230 mAh g(-1) but a slow and continuous capacity fade with cycling. We demonstrate that the K0.5V2O5 compound, with its double-sheet V2O5 layered framework characterized by a large interlayer spacing of 7.7 Å, is the best candidate as positive electrode for lithium battery among the potassium-vanadium bronzes and oxides. A remarkable specific capacity of 210 mAh g(-1), combined with excellent capacity retention, is achieved.