Electrochemical in situ construction of vanadium oxide heterostructures with boosted pseudocapacitive charge storage

Abstract

Pseudocapacitive materials hold extraordinary promise for improving the energy densities of electrochemical capacitors but are often limited to electrodes with ultralow mass loadings (e.g. <1 mg cm⁻²) due to the sluggish mass transport kinetics in thicker electrodes. Here a V₅O₁₂/VO₂ heterojunction nanomaterial with a built-in electric field near the heterointerface is fabricated on a 3D graphite substrate via an in situ electrochemical method for the first time, which can remarkably enhance the capacitive performance by improving the electron/ion delivery kinetics. The V₅O₁₂/VO₂ electrode (mass loading ∼10.8 mg cm⁻²) achieves a high areal capacitance of 5.03 F cm⁻² (465 F g⁻¹) with a good rate capability and long cycle life, outperforming the V₅O₁₂ and VO₂ counterparts, as well as the state-of-the-art reported VO_X electrodes. An asymmetric supercapacitor assembled using V₅O₁₂/VO₂ as the negative electrode and MnO₂ as the positive electrode can deliver high areal/volumetric energy densities of 1.42 mW h cm⁻²/11.85 mW h cm⁻³. An extrapolated gravimetric energy density of 18.6 W h kg⁻¹ can also be achieved, based on the entire weight of the device (76.6 mg cm⁻², active material ratio ∼30%), representing a critical step of pushing pseudocapacitors toward practical applications.