| Lithium ion batteries (LIBs) have attracted a tremendous amount of interest for both transportationand stationary storage applications. Compared with the commercial graphite anodes, titanium dioxide(TiO2) has been demonstrated as potential anode materials for the next generation of high-powerbatteries due to its higher capacity, low cost, excellent cycling performance, and improved safety.However, TiO2also suffers from poor electronic conductivity (10-12~10-7S·cm-1), slow Li+diffusion(10-15~10-9cm2·s-1) in the solid active material and poor rate performance owing to particlesaggregation in the repeated Li+de/intercalation process, which ultimately affect practical applicationsof this materials. Based on the above analysis, some modified approaches have been applied in effortsto improve the electrochemical performance of TiO2in this thesis, including the construction of TiO2micro/nano network structure, and nitrogen-doped reduced graphene oxide hybird materials with highelectrical conductivity and hydrogenated TiO2/reduced graphene oxide composites, the concreteresearch contents are as follows:(1) Micro-/nano-sized TiO2/C composites were prepared using natural polymer nanocrystallinecellulose (NCC) as template and the electrochemical properties of the as-prepared materials weresystematically investigated. The obtained TiO2with nanoparticles morphology could effectively reducelithium ion diffusion path and increase the electrode/electrolyte contact area. Moreover, sucroses areused as carbon precursors to enhance the conductivity of the materials by one-pot hydrothermal route.Electrochemical tests show that the porous micro-/nano-sized conductive network structure TiO2/Ccomposite exhibit supor rate capability and cycle stability.(2) TiO2/nitrogen-doped reduced graphene oxide nanocomposite (TiO2/N-RGO) is prepared via afacile one-pot hydrothermal method, in which ethylene glycol and ammonia are used as the reducingagent and nitrogen precursor, respectively. Electrochemical tests show that the TiO2/N-RGOnanocomposite exhibits superior rate capability and outstanding capacity retention. The reversiblecapacity of the TiO2/N-RGO electrode is up to126.8mAh g-1at10C and still remains at118.4mAhg-1after100cycles with only6.62%capacity loss. The excellent electrochemical performances can beattributed to electronic structure modification of graphene, which promoting intrinsic electron transferbetween the host substrate and electroactive materials. To further enhance the intrinsic conductivity ofTiO2, hydrogenated TiO2/reduced-graphene oxide (H-TiO2/RGO) nanocomposite is synthesised via afacile one-step hydrogenation treatment process. The H-TiO2/RGO nanocomposites reflect much higherrate capability and better capacity retention. At a current rate of1C, the reversible capacity of theH-TiO2/RGO electrode is up to225.3mAh g-1and after100cycles the capacity retention was93.3%.The excellent electrochemical performances are highly related to high electronic conductivity derived from hydrogenated TiO2frameworks and the well-contact zero-dimensional H-TiO2nanoparticle withtwo-dimensional reduced-graphene oxide nanosheets, which efficiently shortened the Li+diffusion pathlengths, enhanced electrolyte-active material contact area and facilitated rapid e-transfer.(3) Mesoporous Li4Ti5O12/carbon nanofibers (LTO/C NFs) are prepared by a facileelectrospinning method combined with soft-template self-assembly. Compared with the regularLTO/C NFs, the mesoporous LTO/C NFs show much higher rate capability and better capacityretention. At a current rate of5C, the reversible capacity of the mesoporous LTO/C NFs electrode isup to127.4mAh g1and still remains at122.7mAh g1after100cycles. The excellentelectrochemical performances are closedly related to well-defined one-dimens ional (1D) mesoporousnanostructure with LTO nanoparticles embedded in the carbon framework, which efficientlyshortened the path length of Li+diffusion, enhanced electrolyte-active material contact area andfacilitated rapid electron transfer. |
