Applying Nanoscale Kirkendall Diffusion for Template-Free, Kilogram-Scale Production of SnO₂ Hollow Nanospheres via Spray Drying System

A commercially applicable and simple process for the preparation of aggregation-free metal oxide hollow nanospheres is developed by applying nanoscale Kirkendall diffusion to a large-scale spray drying process. The precursor powders prepared by spray drying are transformed into homogeneous metal oxide hollow nanospheres through a simple post-treatment process. Aggregation-free SnO₂ hollow nanospheres are selected as the first target material for lithium ion storage applications. Amorphous carbon microspheres with uniformly dispersed Sn metal nanopowder are prepared in the first step of the post-treatment process under a reducing atmosphere. The post-treatment of the Sn-C composite powder at 500 °C under an air atmosphere produces carbon-and aggregation-free SnO₂ hollow nanospheres through nanoscale Kirkendall diffusion. The hollow and filled SnO₂ nanopowders exhibit different cycling performances, with their discharge capacities after 300 cycles being 643 and 280 mA h^-1, respectively, at a current density of 2 A^-1. The SnO₂ hollow nanospheres with high structural stability exhibit superior cycling and rate performances for lithium ion storage compared to the filled ones.