| Titanium based oxide(TiO2, Li4Ti5O12) has been regarded as an excellent material in the present commercial lithium-ion batteries due to its low cost, structural stability, safety, high-rate performance and environmental friendliness. However, the poor Li-ion diffusivity, particles aggregation and sluggish kinetics for charge transfer greatly restrict further development of titanium based oxide electrodes.In this paper, in order to improve its electrochemical properties, the hierarchical porous CNT/TiO2, CNT/Li4Ti5O12 nanocomposites with nanocable and interpenetrating structure have been constructed. The morphologies and structures of the composite materials were characterized by a variety of analysis methods. The electrochemical performance of the composite materials was studied in detail. We discussed the synergy mechanism of electrochemical reaction for two phases in the composite, the relationship between the structures and electrochemical properties, which is a theoretical basis for the research, development and application of new generation anode materials for Li-ion batteries. The concrete research contents are as follows:1. Mixed crystal phases(anatase/rutile) TiO2@CNT porous nanocomposites using TiCl3 and polymer nanotubes as the titanium and carbon source were simply prepared by a two-step hydrothermal process with subsequent heat treatment in nitrogen. As anode materials for lithium-ion batteries, the nanocomposites exhibit the high reversible capacity of 363.6 mAh/g at 100 mA/g after 200 cycles. They have also the excellent rate capability, remarkable electrochemical performance at a broad temperature window with a reversible capacity of 443 mAh/g(55℃) and 84.5 mAh/g(0℃) at 500 mA/g after 300 cycles. Moreover, they display the superior long-term cycling stability at high current density of 2000 mA/g, attaining a high discharge capacity of 153.3 mAh/g for up to 2000 cycles. The enhanced electrochemical performance of the nanocomposites benefits from the few rutile TiO2, which can improve the dispersion rate of the electronic, it is conductive to the rapid transport of lithium ions and electrons.2. The interpenetrating CNT@TiO2 porous nanocomposites were rationally designed by the combination of saturated adsorption, the sol-gel and the subsequent thermal treatment. As anode materials for lithium-ion batteries, the nanocomposites exhibit the high reversible capacity of 523 mAh/g at 100 mA/g after 200 cycles. They have also the excellent rate capability, remarkable electrochemical performance at a broad temperature window with a reversible capacity of 607 mAh/g(55℃) and 188 mAh/g(0℃) at 500 mA/g after 400 cycles. Moreover, they display the superior long-term cycling stability at high current density(2000 mA/g), attaining a high discharge capacity of 189 mAh/g for up to 2000 cycles. Its electrochemical performance is much better than the mixed crystal phases(anatase/rutile) TiO2@CNT nanocomposites, which is attributed to the interpenetrating CNT@TiO2 nanocomposites with the unique interpenetrating structure, abundant multimodal porosity and the high surface area. This unique structure was specifically designed to shorten the diffusion paths of both electronic and ionic transport, and increase the electrode-electrolyte contact area, which are in favor of a rapid charge and discharge processes. Moreover, two components of interpenetrating nanocomposites with different physiochemical properties have generally good compatibility. In addition, nanocomposites with the structure of interpenetrating usually possess macroscopic robustness and homogeneity, nanoscale thickness, mechanical strength and high flexibility. Hence, the electrode is capable of accommodating frequent mechanical strains to continuous energy supply for long time applications in LIBs. These results indicate that interpenetrating CNT@TiO2 porous nanocomposites is a potential candidate for high-power lithium storage.3. The porous CNT@Li4Ti5TiO12 core-sheath coaxial nanocables have been constructed by a sol-gel method combined with a following low temperature reflux process and a short post-annealing. As anode materials for lithium-ion batteries, the nanocomposites exhibit the high reversible capacity of 322.5 mAh/g at 200 mA/g after 200 cycles. They have also the excellent rate capability and the superior long-term cycling stability at high current density, which could attain a high discharge capacity of 198.7 mAh/g at 2000 mA/g for up to 2000 cycles. The enhanced electrochemical performance of the nanocomposites benefits from their unique structure of core-sheath coaxial nanocable, high BET surface area, hierarchical nanopores and the high electronic conductivity. |
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