Preparation of microporous vanadium pentoxide membrane electrodes by phase inversion

Two methods were developed to create microporous membranes of vanadium pentoxide (V₂O₅). In one method, the membranes were made from aqueous solutions of V₂O₅ polymers by phase inversion in acetone. Subsequent supercritical drying removed liquid from the pores to yield a V₂O₅ aerogel with a specific surface area of 165 ± 30 m²/g and a mean pore diameter near 50 nm. However, air-drying destroyed the pore structure to produce a dense V₂O₅ xerogel with a surface area under 10 m²/g. The second method eliminated the need for supercritical drying. The phase inversion of aqueous solutions of V₂O₅ polymers now occurred in a mixture of acetone and propylene carbonate. Partial air-drying removed the acetone, but not the liquid propylene carbonate. The resulting V₂O₅ was a wet gel with a specific surface area of 270 ± 70 m²/g and a mean pore diameter near 40 nm. Scanning electron micrographs of the V₂O₅ gels made by the first and second method showed similar microstructures with randomly entangled fibers. Electrochemical characterization of both materials suggested their performance as cathodes in lithium batteries is limited by electronic conductivity rather than lithium diffusion.