A one-step water based strategy for synthesizing hydrated vanadium pentoxide nanosheets from VO2(B) as free-standing electrodes for lithium battery applications

Abstract

The synthesis of two dimensional (2D) materials from transition metal oxides, chalcogenides, and carbides mostly involve multiple exfoliation steps in which hazardous solvents and reagents are used. In this study, hydrated vanadium pentoxide (V₂O₅·nH₂O) nanosheets with a thickness of a few nanometers were prepared via a facile environmentally friendly water based exfoliation technique. The exfoliation process involved refluxing the precursor, vanadium dioxide (VO₂(B)), in water for a few days at 60 °C. The proposed exfoliation mechanism is based on the intercalation/insertion of water molecules into the VO₂(B) crystals and the subsequent cleavage of the covalent bonds holding the layers of VO₂(B) together. The thermal and chemical analyses showed that the approximate chemical composition of the nanosheets is H_0.4V₂O₅·0.55H₂O, and the percentage of V^V content to that of V^IV in the nanosheets is about 80(3)% to 20(3)%. The exfoliated aqueous suspension of the V₂O₅·0.55H₂O nanosheets was successfully deposited onto multi-walled carbon nanotube (MW-CNT) paper to form free-standing electrodes with a thickness of the V₂O₅·0.55H₂O layer ranging between 45 and 4 μm. A series of electrochemical tests were conducted on the electrodes to determine the cyclability and rate capability of lithium insertion into V₂O₅·0.55H₂O nanosheets. The electrodes with the thinnest active material coating (∼4 μm) delivered gravimetric capacities of up to 480 and 280 mA h g⁻¹ when cycled at current densities of 10 and 200 mA g⁻¹, respectively.