Mo-doped LiV3O8 nanorod-assembled nanosheets as a high performance cathode material for lithium ion batteries†
Mo-doped LiV3O8 nanorod-assembled nanosheets were prepared by a simple hydrothermal reaction of LiOH·H2O, V2O5 and (NH4)6Mo7O24 as precursors followed by thermal annealing. X-ray diffraction results show that the intensity of the (100) peak is less than that of (11) in the Mo-doped LiV3O8 nanosheets, suggesting the inferior crystallinity of Mo-doped LiV3O8. Shifts of Raman bands to lower wavenumbers are found in the Mo-doped LiV3O8 material, which when compared with those of pure LiV3O8 indicates that Mo6+ substitutes V5+ in the LiV3O8 layer. X-ray photoelectron spectroscopy reveals that the Mo-doped LiV3O8 nanosheets calcined at 400 °C contain 25% V4+ and 3.5% oxygen vacancies, which likely compensates for the accommodation of 5% Mo6+. The Brunauer–Emmett–Teller surface area of the Mo-doped LiV3O8 nanosheets calcined at 400 °C is 24.8 m2 g−1, which is nearly double of LiV3O8 calcined at 400 °C (13.9 m2 g−1). The electrochemical and lithium ion intercalation properties of both pure and Mo-doped LiV3O8 cathode were systematically studied using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy. The Mo-doped LiV3O8 cathode shows a much higher lithium ion storage capacity, better cyclic stability, and higher rate capability than the pure LiV3O8 cathode. The maximum discharge capacity of the Mo-doped LiV3O8 (calcined at 400 °C) cathode is 269.0 mA h g−1 and retains 205.9 mA h g−1 at a current density of 300 mA g−1, which is much higher than 97.8 mA h g−1 of the LiV3O8 (also calcined at 400 °C) cathode during the 100th cycle. Note that Mo doping is found to increase the electrochemical reaction reversibility, reduce the electrochemical reaction resistance, and enhance the lithium ion diffusivity. The possible reasons for such significant enhancement in the discharge/charge capacity, cyclic stability and rate performance of the Mo-doped LiV3O8 cathode are elucidated based on the structure analysis.