Binder Free Synthesis of Sulphur Doped Co3V2O8 Nanoarray for Hybrid Asymmetric Supercapacitor Application in Aqueous and Non-Aqueous Medium

Abstract

Metal vanadate are the class of compound for high performance electrochemical charge storage application due to its multiple stable oxidation states, high electrical and ionic conductivity and high rate capability. Among all the metal vanadate, Co3V2O8 is one of the potential candidate due to low cost and environmentally benign nature of cobalt. However, the introduction of Sulfur in Co3V2O8 matrix substantially improves the electrochemical performance by improving the electrical conductivity. Herein, we report Sulfur doped Co3V2O8 (S-Co3V2O8) nanosheet arrays grown on Ni foam hydrothermally without using any binder. As synthesized Co3V2O8 attains nanosheet morphology with height of ~200 nm and thickness of ~10 nm. We note that the shape and size of S-Co3V2O8 nanosheet arrays remain unchanged after the doping of sulfur in Co3V2O8. Further, the thickness of nanosheet increases with increasing reaction time. We observed that the electrochemical performance of S-Co3V2O8 nanosheet array is ~25% better than the undoped Co3V2O8 nanosheet arrays. In aqueous alkaline electrolyte, S-Co3V2O8 nanosheet array exhibits a specific capacity of 1476 C/g (3690 F/g) at 2 A/g with enhanced rate capability and an excellent capacity retention of 94.2% at 5 A/g specific current after 4000 cycles. The doping of sulfur improves the electrochemical performance due to its low electronegativity and large size as compared to oxygen, which creates a robust structure, better transport properties and improved charge storage capacity. An asymmetric supercapacitor fabricated using S-Co3V2O8 nanosheet arrays as cathode and activate carbon (AC) as anode shows high specific capacity (or capacitance) of 174.5 C/g (or 116.33 F/g), energy density (36.4 Wh/kg) and power density (740 W/kg) at 2 A/g with 98.4% capacity retention after cycles. Further, Li-ion hybrid capacitor fabricated in the CR2032 coin cell exhibits specific capacity of 994 mAh/g with energy density of 695 W/kg at specific current of 1 A/g with good rate capability and 46.5% capacity retention after 100 cycles renders it as a potential candidate for future high energy storage system with long term durability.