VO2 nanoflake arrays for supercapacitor and Li-ion battery electrodes: performance enhancement by hydrogen molybdenum bronze as an efficient shell material

Abstract

Hydrogen molybdenum bronze (HMB) is electrochemically deposited as a homogeneous shell on VO₂ nanoflakes grown on graphene foam (GF), forming a GF + VO₂/HMB integrated electrode structure. Asymmetric supercapacitors based on the GF + VO₂/HMB cathode and neutral electrolyte are assembled and show enhanced performance with weaker polarization, higher specific capacitance and better cycling life than the unmodified GF + VO₂ electrode. Capacitances of 485 F g⁻¹ (2 A g⁻¹) and 306 F g⁻¹ (32 A g⁻¹) are obtained because of the exceptional 3D porous architecture and conductive network. In addition, the GF + VO₂/HMB electrodes are also characterized as the cathode of lithium ion batteries. Very stable capacities at rates up to 30 C are demonstrated for 500 cycles. This new type of shell material is expected to have its generic function in other metal oxide based nanostructures.