| Energy shortage and environment pollution are two major crisises the global community has to face in the21st century for the sustainable development of the human society. In fact, sustainable energy storage techniques have been regarded as one of the most effective and green way to sovle these problems. Among them, alkali metal-ion batteries, including lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) represent two of the most promising techniques due to their environmental friendliness, safety, high energy density and long life. The key factor that determines the performance of a battery is the electrode material. To achive a high performance, it is highly important to develop a suitable electrode material. This thesis focuses on the study of the preparation and electrochemical behavior of lithium and/or sodium insertion into nanostructured TiO2and carbon-based TiO2composites. The main findings are as follows:A one-pot and fast microwave-assisted solvothermal (MAS) method has been developed for the preparation of nanosheet-assembled TiO2-B spheres (TBNSs) using [Bmim][BF4] as a soft template. The morphology and phase of the as-obtained TiO2nanostructures can be readily adjusted by altering the temperature, reaction time, and reactant concentration. The hierarchically nanostructured TBNSs show enhanced rate performance and cyclability as an anode material for LIBs, due to the stable nanostructure, large surface area, nanoporous nature, and fast pseudocapacitive reaction of TiO2-B nanosheets. It is expected that the conceptual development of microwave-heating techniques may bring about the replace of conventional heating in many solution-based reactions, shortening the reaction time and improving the product quality of TiO2-B for next-generation of rechargeable batteries in high-power applications.A novel hybrid nanoarchitecture, CNTs strongly coupled with TiO2-B nanosheet arrays (CNTs@TiO2-B NSs) was prepared in the present of [Bmim][BF4] room temperature ionic liquid. The unique structural features of the hybrid CNTs@TiO2-B NSs including effective transport pathways for electrons and Li ions along CNTs, porous nature, large specific surface area and stability of the1D nanoarchitecture, together with the fast pseudocapacitive feature and reduced ion-diffusion length of thin TiO2-B nanosheet arrays, contribute to the superior capacity, cyclability and rate capability. We believe that the easy ionic liquid-guiding approach can be applied to fabricate other hybrid materials. The concept of combining the fabrication of unique hybrid nanoarchitectures with polymorphs having a pseudocapacitive behavior is general for developing other electrode materials.To determine the fundamental phase-related energy storage properties of TiO2, a microwave-assisted acid treated technique for fabricating TiO2nanobelts with tunable phase proportion of TiO2-B and anatase along with detailed kinetic analysis has been presented. The materials exhibit a phase-dependent pseudocapacitive behavior, demonstrated by a linear relationship between the TiO2-B phase proportion and capacitive charge. The TiO2-B phase with open tunnels along the b and c-axes provides a qusi-2D channel for lithium transport, which is much like the surface adsorption reactions of lithium. These features contribute to a fast pseudocapacitive behavior. In contrast, the lithium storage behavior in anatase with narrower tunnels is dominated by the slow solid-state diffusion and goes through a phase transformation process, both of which are adverse to pseudocapacitance. The phase-dependent pseudocapacitive behavior can be rationalized by the distinct structure-related behavior of lithium in the two host structures.A large-scale and cost-effective approach has been developed for the fabrication of N/B co-doped nanotube-constructed TiO2spheres (NT-T) with TiO2-B/anatase mixed phases. Based on systemic investigations on the dependence of structure factors on the rate performance by several advanced electrochemical techniques and first-principle calculations, it is found that the TiO2-B/anatase grain interfaces contribute to additional interface lithium storage. In addition, the N/B co-doping would benefit the fast transport of both electrons and Li+ions, resulting in enhancement of electronic and ionic conductivities simultaneously. The combination of these merits contribute to an outstanding rate capability, demonstrated by160mAh g-1at60C, representing one of the best rate performances among all Ti-based anodes. From a fundermental point of view, the demonstrated relsults are also important, particularly to reveal the relationship between rate performance and structure and offer guilines for the design of high-rate electrode materials.A hybrid material, graphene coupled TiO2, was prepared and evaluated as an anode material for SIBs, exhibiting a superior rate capability and cyclability exceeding all electrode materials reported to date. Interestingly, a Na+intercalation pseudocapacitance dominated charging process was revealed, which contributes much to the superior rate capability and cyclability of the hybrid. First principle calculations further evidence that the hybridization of graphene with TiO2reduces the diffusion barrier, hence favors the sodium intercalation pseudocapacitive process. This work demonstrates that it is highly promising to exploit electrode materials featuring intercalation pseudocapacitance to achieve SIBs with low cost, high rate and long life. |
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