Solvothermal Synthesis Of Hierarchical Metal Oxide Nanomaterials As Lithium-ion Battery Anodes

Lithium ion battery(LIB) has achieved great commercial success in portable electronic devices, hybrid electric vehicles(HEV), and electric vehicles(EV) due to high specific capacity, high working voltage, outstanding energy density, and environmental benignity. However, graphite, the commercial LIB anode, has a high propensity to form lithium dendrites during repeated charging/discharging processes due to its low intercalation potential, which brings severe safety concerns. In addition, the low specific capacity of graphite cannot meet the rapidly increasing technical requirement. Thus, it has been one of the central issues to develop new generation of lithium-ion battery anode to replace graphite with high specific capacity, good energy density output, excellent cyclic stability, and good operation safety. Titania is one of the most promising lithium-ion battery anode due to its abundance, structural stability, and good safety. Nevertheless, the inherent poor electron conductivity and Li+ diffusion ability inhibit its practical capacity, which limits its practical usage. Generally, two approaches are introduced to resolve these problems: synthesis of nano-structured titania or compositing with conductive matrix like carbonaceous materials. Our research is to combine the two approaches together to synthesize hierarchical titania/carbon nanohybrids. Following is the main content of the research:1. Hierarchical porous titania/carbon nanohybrid microspheres are synthesized through a facile method. Polystyrene, used as the templating agent and carbon source, is first dissolved in N, N? dimethyl formamide(DMF). Concentrated hydrochloric acid(HCl) and titania precursor--titanium tetraisopropoxide(TTIP) are then added in the solution. Assisted by solvothermal treatment, TiO2/PS microspheres are formed due to the integration of titania nanoparticles within the PS microspheres. The as-prepared samples are finally converted to TiO2/C microspheres under argon calcination. The carbon content of the microspheres can be controlled through further annealing in air. Systematic studies have been performed to unveil the mechanism for the formation of TiO/PS microspheres, structure and morphology characterization, and electrochemical performance as lithium-ion battery anode and photocatalyst for hydrogen conversion through catalytic water splitting under light illumination.2. A template free method has been developed to synthesize hierarchical TiO2 microspheres with different morphologies. Assisted by solvothermal reaction in 1, 4-dioxane, four different micro/nano structures can be obtained with increasing concentrations of concentrated HCl: microspheres, nanorod@sphere, nanorodspheres, nanorod cauliflowers. Crystalline TiO2 structures are obtained after calcination in air. The mechanism for the template free synthesis the hierarchical TiO2 microspheres is investigated. And the electrochemical performance of the TiO2 microspheres as lithium-ion battery anode and photo catalyst for hydrogen conversion is studied. The structureproperty correlation of the TiO2 microspheres is discussed.