Facile synthesis of hierarchical and porous V2O5 microspheres as cathode materials for lithium ion batteries.

Hierarchical and porous V2O5 microspheres have been fabricated by a refluxing approach followed by annealing in air. The resulting porous V2O5 microspheres typically have diameters of 3-6 µm and are constructed of intertwined laminar nanocrystals or crosslinked nanobricks. It is found that the vanadyl glycolates rinsed with water have pronounced pore structures than that rinsed with ethanol alone. In addition, the configuration of the vanadyl glycolates microspheres can be tuned during the refluxing along with stirring. The possible formation processes of the vanadyl glycolates and V2O5 products have been discussed based on the experimental data. Electrochemical tests indicate that the hierarchical and porous V2O5 microspheres exhibit relatively high and stable Li(+) storage properties. The porous V2O5 microspheres assembled by intertwined nanoparticles maintain reversible Li(+) storage capacities of 102 and 80 mAh g(-1), respectively; whilst the porous V2O5 microspheres assembled by crosslinked nanobricks maintain reversible Li(+) storage capacities of 100 and 85 mAh g(-1) over 100 cycles at current rates of 0.5 and 1 C, respectively. The superior Li(+) storage performance of the hierarchical and porous V2O5 microspheres could mainly be ascribed to the improved electrode/electrolyte interface, reduced Li(+) diffusion paths, and relieved volume variation during lithiation and delithiation processes.

Facile and fast synthesis of porous TiO2 spheres for use in lithium ion batteries.

Porous anatase TiO2 spheres have been synthesized by a microwave-assisted hydrothermal reaction of spherical particle precursors followed by annealing in air. The synthesized TiO2 spheres are formed by interconnected nanocrystals with size of 8.7 nm in average and have grain diameters of 250-400 nm. After annealing at 500°C, the TiO2 samples maintain spherical shape and develop highly mesoporous characteristics with a specific surface area of 151 m(2) g(-1). The TiO2 samples annealed at 750°C consist of larger aggregated particles with diameters of 500-900 nm and still retain mesoporous anatase structure, but with a reduced specific surface area of 25.6 m(2) g(-1). Electrochemical studies reveal that the porous TiO2 spheres annealed at 500°C own very high and stable lithium ion (Li(+)) storage capacities of 207, 184, 166, and 119 mA h g(-1) at 0.5, 1, 2, and 5C (850 mA g(-1)) rates, respectively, owing to their highly porous nanostructures and fine spherical morphology. In contrast, the TiO2 spheres annealed at 700°C exhibit modest electrochemical performance due to their reduced pore structures and larger crystallite size. The prepared porous TiO2 spherical particles show great promise for use as high performance anode materials for lithium ion batteries (LIBs).