Mo-doped LiV3O8 nanorod-assembled nanosheets as a high performance cathode material for lithium ion batteries

Abstract

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 100^th 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.