Kilogram-scale production of SnO₂ yolk-shell powders by a spray-drying process using dextrin as carbon source and drying additive

A simple and general method for the large-scale production of yolk-shell powders with various compositions by a spray-drying process is reported. Metal salt/dextrin composite powders with a spherical and dense structure were obtained by spray drying and transformed into yolk-shell powders by simple combustion in air. Dextrin plays a key role in the preparation of precursor powders for fabricating yolk-shell powders by spray drying. Droplets containing metal salts and dextrin show good drying characteristics even in a severe environment of high humidity. Sucrose, glucose, and polyvinylpyrrolidone are widely used as carbon sources in the preparation of metal oxide/carbon composite powders; however, they are not appropriate for large-scale spray-drying processes because of their caramelization properties and adherence to the surface of the spray dryer. SnO₂ yolk-shell powders were studied as the first target material in the spray-drying process. Combustion of tin oxalate/dextrin composite powders at 600°C in air produced single-shelled SnO₂ yolk-shell powders with the configuration SnO ₂@void@SnO₂. The SnO₂ yolk-shell powders prepared by the simple spray-drying process showed superior electrochemical properties, even at high current densities. The discharge capacities of the SnO₂ yolk-shell powders at a current density of 2000mAg^-1 were 645 and 570mAhg^-1 for the second and 100th cycles, respectively; the corresponding capacity retention measured for the second cycle was 88%. Not just an empty shell: Tin oxalate/dextrin composite powders were produced on a large scale by means of a commercial spray-drying process and transformed into single-shelled SnO₂ yolk-shell powders by combustion in air at 600°C (see figure). The SnO₂ yolk-shell powders showed superior electrochemical properties as anode materials for lithium-ion batteries.