Amorphous V₂O₅/carbon composites as electrochemical supercapacitor electrodes

High rate intercalation electrode performance of V₂O₅ gel/carbon composites has been demonstrated. A V₂O₅ sol was prepared by a reaction of metallic vanadium with a hydrogen peroxide solution. Acetylene black powder was added into the sol with acetone to yield a homogeneous suspension. A composite of amorphous V₂O₅ and carbon was loaded on a macroporous nickel current collector, and heat-treated at 120 °C to obtain a sample electrode. Electrochemical measurements were performed in some organic electrolytes like LiClO₄/PC or LiPF₆/γ-butyrolactone (γ-BL) at room temperature. It was confirmed that a composite electrode with the V₂O₅/carbon ratio of 0.7 in weight showed 54% of the ideal capacity, 360 mA h/g (4.2-2.0 V) based on V₂O₅, even at a very high rate discharge at 150 C or 54 A/g V₂O₅. The diffusion length of this host-guest system was estimated as 30-50 nm by means of a simulation of the discharge curves using a diffusion model assuming D̃=10^-12 cm²/s. The reversibility was also satisfactory and no capacity loss was observed after thousands of times of discharge/charge cycles between 4.2 and 3.0 V at the rate of 20 C. A prototype electrode was fabricated by coating a thin layer of the composite on an Al sheet current collector using an applicator. It showed the capacity of 40 mA h/g electrode at a current density as high as 30 mA/cm².