Electrochemical properties of spherical hollow SnO₂-TiO₂-C composite powders prepared by spray pyrolysis

Hollow spherical SnO₂-TiO₂-C composite powders with uniform compositions are prepared by spray pyrolysis from precursor solutions containing Sn and Ti compounds along with citric acid and ethylene glycol. The prepared composite powders are subsequently heat-treated at various temperatures. Samples treated at 400°C show the presence of amorphous structures and fine crystallites with sizes ranging to a few nanometers. Crystalline peaks corresponding to rutile-like crystal structures are observed in the XRD patterns of the composite powders treated at 600°C. The peaks in the XRD patterns of the SnO₂ phase with the rutile structure marginally shift to higher angles because of the formation of the SnO₂-TiO₂ solid solution. Crystals with sizes below 10 nm present in composite powders treated at 600°C are coated with a layer of amorphous carbon. Phase separation of Sn and Ti components dose not occur during the crystallization of the composite powders by heat-treatment. The cycle performances of the SnO₂-TiO₂-C composite powders are better than that of pure SnO₂ powders at a constant charge and discharge rate of 700 mA g^-1 in the voltage range 0.01-3.0 V. The discharge capacities after 50 cycles for the composite powders treated at 600°C are 394, 396, 327, and 244 mAh g^-1 at discharge rates of 300, 1400, 2100, and 3500 mA g^-1, respectively.