Sol-gel synthesized carbon-coated vanadium borate as anode material for rechargeable Li and Na batteries

Transition metal borates, attracting researchers to investigate whether they can exhibit Li cycling similar to the metal oxides, were criticized for their poor electrochemical reversibility. Herein, citric acid assisted sol-gel technique had been used to synthesize high-performance VBO3 anode for Li-ion batteries. High-purity and well-crystallized VBO3 particles covered with amorphous carbon layer (VBO3/carbon) were applied as electrodes for both rechargeable Li and Na batteries. In the Li system, the VBO3/carbon composite delivered a high reversible capacity of 859.5 mA h g−1 in the first cycle, and showed an outstanding rate ability of ∼720 mA h g−1 even at a current density of 200 mA g−1, which suggests both V and B in VBO3 had participated in the electrochemical redox reaction during the Li intercalation and extraction. However, the Na storage of VBO3/carbon after conversion reaction exhibited typical capacitance behavior but poor electrochemical reversibility.