Carbon-free hydrated cobalt vanadium oxide as a promising anode for lithium-ion batteries

Recently, cobalt vanadium oxide (CoV2O6 or CVO), a transition metal-incorporated vanadium oxide, is proposed as a promising anode material for lithium-ion batteries (LIBs). Although introducing cobalt ions into vanadium oxide improves the electrical conductivity and structural stability, gradual structural deterioration compromises the long-term performance of CVO. In this study, hydrated CVO (CoV2O6·4H2O or CVO4H) is synthesized through a simple coprecipitation method, where Li-ion insertion/deinsertion is facilitated in the hydrated structure and the diffusion kinetics are enhanced relative to those of plain CVO. The presence of crystal water molecules in CVO4H increases the interplanar spacing of CVO, enhances the structural stability, and facilitates Li-ion diffusion. To systematically verify these characteristics, various electrochemical analyses (electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, and cyclic voltammetry) are performed. As-synthesized CVO4H exhibits high electrochemical performance (1141/1157 and 1078/1090 mAh g−1 at current densities of 100 and 500 mA g−1 after 200 and 300 cycles) with stable Li-cycling life and good rate capability (capacity retention of ∼70% at 10 A g−1 relative to 0.1 A g−1), without added carbon in the active material. Consequently, CVO4H is a promising candidate material for next-generation LIB anodes.