Preparation And Applications In Lithium Ion Battery Of CNT@TiO₂Composite Nanocables

Carbon nanotubes （CNTs） have unique electrical, mechanical and thermal properties,which have been widely used in many ifelds，such as nanoelectronics, sensing，photocatalysisand lithium-ion batteries et al. It is still a challenge to develop simple methods to large scalesynthesize CNTs. Recently, a novel bamboo-like polymer nano tubes were reported, whichcan be effectively prepared on large scale and low cost. In this thesis, bamboo-like CNTs,TiO₂nanotubes and CNT@TiO₂coaxial nanocables were prepared by a sol-gel method andpost-calcination in presence of polymer nanotubes acting as both a template and carbonsource. These as-synthesized materials were applied in lithium-ion batteries, theirelectrochemical properties were investigated.Sulfonation of polymer is a common method for introducing hydrophilic groups on thesurface of polymer material. The polydivinylbenzene （PDVB） nanotubes were sulfonated inconcentrated sulifiric acid and stirred at50°C. Based on FT-IR spectra, TEM and thedispersion experiment, the polymer nanotubes have been successfully sulfonated, whichpreserves the bamboo-like nanotube structure. The dispersion of sulfonated polymernanotubes is greatly improved in the water. A phenomenon was found that the sulfonaetdPDVB （SPDVB） nanotubes were carbonized in inert atmosphere, bamboo-like carbonnanotubes （CNTs） were obtained. However, when non-sulfonted PDVB nanotubes werecarbonized at the same situation, the irregular large bulk carbon materials were obtained.What’s more，the effects of sulfonation time and pyrolysis temperature on the CNTs’morphology and electrochemical performance have been discussed. The results indicate thatthe CNTs obtained at900°C have the BET surface area of480m²g^-1，the wall of CNTscontains lots of mciropores of0.55nm. Moreover, the CNTs electrode exhibits a highreversible capacity of230mA h "1g under the conditi1ons of1000mAg^-1 up to300cycles，which is a potential candidate for lithium ion battery anode materials.Atfer the polymer nanotubes were sulfonated, on the one hand, the dispersion of polymer nanotubes in ethanol and water is greatly enhanced, on the other hand, the surface of polymernanotubes produces the hydrophilic layer with sulfonic acid groups, which are capable ofadsorption or forming complexes with a large variety of tfinctional components such as metalions，metal oxide precursors and basic inorganic precursors, etc. The CNT@TiO₂core/sheathcoaxial nanocables and TiO₂nanotubes have been successfully prepared by gel inducedfavorable hydrolysis of tetrabutyl titanate （TBT） and post-calcination. The effects of thesulfonation time, the feeding amount of TBT and carbonized temperature on the morphology,composition and electrochemical performance of the CNT@TiO₂composite have beensystematically discuss. The results are as follows:0.1g SPDVB nanotubes sulfonated at50。Cfor12h and1.33g TBT were dispersed in10ml of ethanol and was placed in0°C ice bathfor the hydrolysis，the SPDVB@titania-gel nanocables with a titania-gel sheath thickness of110?120nm were obtained. Atferwards, the CNT@TiO₂nanocables were obtained bycalcinating SPDVB@titania-gel nanocables at700°C for2h in N2atmosphere. When actingas lithium ion battery anode materials, the CNT@TiO₂composite exhibits a high reversibleca"1pacity of231mA h g under the conditions of1000mA "1g up to100cycles, which possessthe higher capacity than that of CNT@TiO₂composites at other temperature, previously1reported materials and as-prepared pure TiO₂nanotubes (70mA hg^-1). The pore sizedistribution shows that The CNT@TiO₂composite includes micropores （0.4-2nm）,mesopores （2-6and10-50nm） and macropores （50-200nm）, guaranteeing suiffciently rapidtransport of both ions and electronic. The micropores and macropores in the compositesmainly come rfom the CNT core，and the mesopores mainly come rfom the TiO₂sheath. Themultiple pores can increase the electrode/electrolyte contact area, shorten the diiffision pathsof ion transport. Moreover, the CNT@TiO₂composite nanocables take on a stable cycleperformance both at high temperature （50。C） and low temperature （0°C）.