Síntese e caracterização de pentóxido de vanádio (V 2 O 5 ) dopado com óxido de zinco (ZnO) para aplicação como cátodo em baterias de íons de lítio

Abstract

his study aimed to synthesize and characterize vanadium oxide gels (V 2 O 5 ) doped with zinc oxide (ZnO). These materials are part of a special class of vanadium oxides, and have been studied with emphasis on their application as active material in lithium ion batteries. Vanadium oxide gels were synthesized by the sol-gel technique. In this route, the sol (aqueous solution formed by molecular precursors) evolves through hydrolysis and condensation reactions to a state known as gel. The gels were made from aqueous solutions of V 2 O 5 and H 2 O 2 at temperature of 63 ° C. The doping of the gels occurred through the addition of ZnO to the solution. After the synthesis the gels were impregnated onto FTO substrates in order to form the xerogels of V 2 O 5 . The xerogels were annealed at 393 K and 723 K and characterized by scanning electron microscopy (SEM), X ray diffraction (XRD), cyclic voltammetry and chronopotenciometry. The x ray diffraction indicated that the ZnO doping does not affect the long-range order of the samples even after annealing at 393 K and 723 K. This implies that the ZnO is dispersed in oxide structure. Analysis by SEM showed that the surface morphology of the xerogel is not dependent on dopant concentration. The surface is formed by interconnected vanadium oxide chains, independently of annealing temperature. However, after the intercalation of lithium ions, the surface of the samples presents micropores, precipitates and rods. Cyclic voltammetry showed that lithium ions are intercalated in the structure of xerogels. The best results were obtained for the sample doped with 5 mol% of ZnO. In this case we observe the invariance of the electrochemical efficiency of oxide even after twenty consecutive scan. Moreover, the cyclic voltammetry results correlate the enhanced electrochemical results to the presence of dopant and annealing temperature. The results of chronopotenciometry confirm the trend observed in the analysis of cyclic voltammetry. The doped ZnO affects the specific capacity of the samples. Compared to the standard undoped sample, the sample doped with the highest ZnO concentration of ZnO presented capacities around 480 mAh/g in the first cycle of charge/discharge. However, in all cases the specific capacity falls at consecutive cycles. Finally, although we have observed improved electrochemical efficiency with annealing temperature, this was not verified in chronopotentiometry measurements which indicate the decrease of capacity with increase of annealing temperature.