ELECTROCHEMICAL SODIUM INTERCALATION IN NA0.33V2O5 BRONZE SYNTHESIZED BY A SOL-GEL PROCESS

Electrochemical sodium intercalation in Na0.33V2O5 bronze prepared by a sol-gel process (SGP bronze) is studied at room temperature in a sodium-based non aqueous electrolyte. Sodium occupancy inside the β-Na0.33V2O5 lattice proceeds in a similar manner to that of Li intercalation, i.e., in the available sites of the tunnel structure of the bronze, which corresponds to a maximum uptake of about 1.6 Na+ per mole of sodium bronze. The enhancement of the structural anisotropy obtained by the sol-gel method induces a better electrochemical behaviour, as compared with that of the similar bronze synthesized through solid state reactions at high temperature (SSR bronze). The chemical diffusion coefficient of Na+ ions, DNa+ is found to be one or two orders of magnitude lower than of Li+ ions. A satisfactory reversibility of Na+ ion insertion is obtained when cycling experiments are performed in the potential window 3.6/2.4 V at 30 μA/cm2, since about 65% of the initial capacity is recovered after the 30th cycle, i.e., 50 Ah kg-1.