Vanadium metal-organic frameworks derived VOx/Carbon nano-sheets and paperclip-like VOx/nitrogen-doped carbon nanocomposites for sodium-ion battery electrodes

In this work, vanadium metal-organic framework derived VOx/carbon and VOx/N-doped carbon nanocomposites are presented. The methodology introduced here is based on a novel polyol synthesis of vanadium metal-organic frameworks (MOFs) involving a microwave-assisted solvothermal reaction of vanadyl acetylacetonate with biphenyl-4,4′-dicarboxylic acid (Bpdc) and/or 2,2′-bipyridine-4,4′-dicarboxylic acid (NBpdc) in diethylene glycol (DEG) at the temperature of 230 °C. The V-based MOFs, labeled as V-Bpdc and V-NBpdc, were used as precursors for the preparation of VOx/carbon and VOx/N-doped carbon nanocomposites with unique sponge-like nano-sheet and paperclip-like morphology, respectively. The nanocomposites were obtained via thermal transformation of as-prepared vanadium MOFs in the argon atmosphere at 600 °C. The VOx/carbon sample consists of nano-sheets with the thickness 5–20 nm while the VOx/N-doped carbon paperclip-like nanocomposite has a rod diameter 35–70 nm. It was found that the approach reported here provides an effective and simple preparation pathway of carbon-based nanocomposites containing homogeneously distributed VOx species. Both V-MOFs and V-MOF-derived nanocomposites were characterized by the variety of physicochemical methods. In the following step, the obtained nanocomposites were investigated as electrode materials in sodium-ion batteries. Based on the obtained results, high electrochemical activities of VOx/carbon and VOx/N-doped carbon nanocomposites were evidenced. Particularly, in the case of VOx/N-doped carbon-based electrode, high capacity and low irreversible capacity were achieved. Therefore, reported materials are found to be promising candidates for electrode materials in sodium-ion batteries.