Unique-structured composite microspheres of carbon and MoTe were prepared by a two-step process. Precursor C-MoO composite microspheres were prepared by spray pyrolysis, and then the precursor was transformed into C-MoTe composite microspheres by a tellurization process. C-MoTe composites with a uniform distribution of MoTe nanocrystals (C/MoTe) and core-shell-structured C-MoTe composites (C@MoTe) were synthesized at tellurization temperatures of 450 and 600 °C, respectively. At a higher tellurization temperature of 600 °C, all of the MoTe nanocrystals moved to the surface of the microsphere because of the Ostwald ripening process. The initial discharge capacities of the C/MoTe, C@MoTe, and bare MoTe (i.e., containing no carbonaceous materials) powders for Na-ion storage at a current density of 1.0 A g were 328, 388, and 341 mA h g, respectively. The discharge capacities of the C/MoTe, C@MoTe, and bare MoTe powders for the 200 cycle were 241, 286, and 104 mA h g, respectively, and the corresponding capacity retentions, which were measured from the second cycle were 100%, 99%, and 37%, respectively. The high structural stability and well-developed two-dimensional layer of MoTe of the C@MoTe microspheres provide superior Na-ion storage properties compared to those of the C/MoTe microspheres and bare MoTe powder.

NiO nanofibers composed of hollow NiO nanospheres with different sizes were prepared by electrospinning method. The mean size of the hollow NiO nanospheres was determined by the mean size of the Ni nanocrystals of the Ni-C composite nanofibers formed as an intermediate product. Porous-structured NiO nanofibers were also prepared as a comparison sample by direct oxidation of the electrospun nanofibers. The discharge capacities of the nanofibers composed of hollow nanospheres reduced at 300, 500, and 700 °C for the 250th cycle were 707, 655, and 261 mA h g(-1), respectively. However, the discharge capacity of the porous-structured NiO nanofibers for the 250th cycle was low as 206 mA h g(-1). The nanofibers composed of hollow nanospheres had good structural stability during cycling.

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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 g−1, respectively, at a current density of 2 A g−1. The SnO2 hollow nanospheres with high structural stability exhibit superior cycling and rate performances for lithium ion storage compared to the filled ones.