Titania-carbon nanocomposite anodes for lithium ion batteries--effects of confined growth and phase synergism

Large-Scale Synthesis and Lithium Storage Performance of Multilayer TiO2 Nanobelts

Titanium dioxide (TiO2) has been widely investigated as the electrode material for lithium ion batteries (LIBs), due to its low cost, small volume expansion, and high environmental friendliness. However, the fading capacity and short cycle life during the cycling process lead to poor cycling performance. Herein, multilayer TiO2 nanobelts with a high specific surface area and with many pores between nanoparticles are constructed via a simple and large-scale approach. Benefiting from the multilayer nanobelt structure, as-prepared TiO2 nanobelts deliver a high reversible capacity, strong cycling stability, and ultra-long cycle life (~185mAhg−1 at 500mAg−1 after 500 cycles) as electrode materials for LIBs.

Direct Imprinting of Scalable, High-Performance Woodpile Electrodes for Three-Dimensional Lithium-Ion Nanobatteries

The trend of device downscaling drives a corresponding need for power source miniaturization. Though numerous microfabrication methods lead to successful creation of submillimeter-scale electrodes, scalable approaches that provide cost-effective nanoscale resolution for energy storage devices such as on-chip batteries remain elusive. Here, we report nanoimprint lithography (NIL) as a direct patterning technique to fabricate high-performance TiO₂ nanoelectrode arrays for lithium-ion batteries (LIBs) over relatively large areas. The critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current densities as high as 5000 mA g^-1. In addition, by sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily made in a "stack-up" manner. The height of architecture can be easily controlled by the number of stacked layers while maintaining nearly constant surface-to-volume ratios. The result is a proportional increase of areal capacity with the number of layers. The structure-processing combination leads to efficient use of the material, and the resultant specific capacity (250.9 mAh g^-1) is among the highest reported. This work provides a simple yet effective strategy to fabricate nanobatteries and can be potentially extended to other electroactive materials.

An Unprecedented Case: A Low Specific Surface Area Anatase/N-Doped Carbon Nanocomposite Derived from a New Single Source Precursor Affords Fast and Stable Lithium Storage

A nanocomposite of ultrafine anatase nanoparticles (<5 nm) embedded N-doped carbon (TiO₂-NPs/NC) with a relatively low specific surface area was successfully synthesized by in situ pyrolysis of a new and cheap single source precursor of (H₂en)₃[Ti₄(O₂)₄(Hcit)₂(cit)₂]·12H₂O (en = ethylenediamine and H₄cit = citric acid) under 550 °C and an inert atmosphere. The precursor in crystalline state was isolated from an aqueous solution containing of titanium butoxide, citric acid, hydrogen peroxide, and ethylenediamine and was characterized. The crystal structure was determined by X-ray single crystal diffraction. To our surprise, the low surface area TiO₂-NPs/NC exhibits a high specific capacity, superior rate capability, excellent cycle performance, and good processability as a negative material for rechargeable lithium-ion batteries (LIBs). A large reversible capacity of 360 and 125 mA h g^-1 and a high Coulombic efficiency (the average value is ∼99.8%) could be kept even after 1000 cycles under a current density of 0.3 and 6 A g^-1, respectively. An analysis of the voltammetric sweep data shows that the pseudocapacitive behavior occurred at the surface of the material and the lithium intercalation processes contribute to the total stored charge, resulting in the high capacity of the TiO₂-NPs/NC nanocomposite. The potentiostatic intermittent titration technique used to determine the lithium ion diffusion (D_Li+) suggested the TiO₂-NPs/NC nanocomposite displays a high D_Li+. In addition, the high electric conductivity provided by the NC substrate and the ultrafine anatase particles can mitigate the diffusion path for electrons and ions and tolerate higher strain, and thus effectively decrease pulverization and improve the rate and cycle performance. In particular, the observed superior lithium storage properties, resulting from the low surface area nanocomposite with ultrafine nanoparticles embedded NC substrate, are expected to have fundamental and practical implications for the preparation of high performance electrodes in LIBs or other cells.

A hierarchically structured anatase-titania/indium-tin-oxide nanocomposite as an anodic material for lithium-ion batteries

A nanotubular titania/ITO nanocomposite is synthesized, exhibiting enhanced electrochemical performance as an anodic material for lithium-ion batteries.

Oxygen vacancy induced fast lithium storage and efficient organics photodegradation over ultrathin TiO2 nanolayers grafted graphene sheets

In this work we have developed a unique structure of ultrathin (5nm) TiO2 nanolayers grafted graphene nanosheets (TiO2/G) and integrated oxygen vacancy (VO) into TiO2 to enhance its lithium storage and photocatalytic performances. The defective TiO2/G was synthesized by a solvothermal and subsequent thermal treatment method. When treated in a H2 atmosphere, the resulting TiO2-x/G(H2) has lower crystallinity, smaller crystal size, richer surface VO, higher surface area, larger pore volume, and lower charge transfer resistance than that reduced by NaBH4 solid, i.e., TiO2-x/G(NaBH4). More importantly, the surface VO in the TiO2-x/G(H2) could remarkably inhibit the recombination of photogenerated electron-hole pairs compared with the bulk Vo in the TiO2-x/G(NaBH4). As a result, the combination of all the factors contributed to the superiority of TiO2-x/G(H2), which demonstrated not only 70% higher specific capacity, longer cycling performance (1000 cycles) and better rate capability for lithium-ion battery, but also higher photocatalytic activity and 1.5 times faster degradation rate for organic pollutants removal than TiO2-x/G(NaBH4). The findings in this work will benefit the fundamental understanding of TiO2/G surface chemistry and advance the design and preparation of functional materials for energy storage and water treatment.

Soft-Templated Self-Assembly of Mesoporous Anatase TiO2/Carbon Composite Nanospheres for High-Performance Lithium Ion Batteries

Mesoporous anatase TiO2/carbon composite nanospheres (designated as meso-ATCCNs) were successfully synthesized via a facile soft-templated self-assembly followed by thermal treatment. Structural and morphological analyses reveal that the as-synthesized meso-ATCCNs are composed of primary TiO2 nanoparticles (∼5 nm), combined with in situ deposited carbon either on the surface or between the primary TiO2 nanoparticles. When cycled in an extended voltage window from 0.01 to 3.0 V, meso-ATCCNs exhibit excellent rate capabilities (413.7, 289.7, and 206.8 mAh g(-1) at 200, 1000, and 3000 mA g(-1), respectively) as well as stable cyclability (90% capacity retention over 500 cycles at 1000 mA g(-1)). Compared with both mesoporous TiO2 nanospheres and bulk TiO2, the superior electrochemical performance of the meso-ATCCNs electrode could be ascribed to a synergetic effect induced by hierarchical structure that includes uniform TiO2 nanoparticles, the presence of hydrothermal carbon derived from phenolic resols, a high surface area, and open mesoporosity.

New Approach to Create TiO2(B)/Carbon Core/Shell Nanotubes: Ideal Structure for Enhanced Lithium Ion Storage

To achieve uniform carbon coating on TiO2 nanomaterials, high temperature (>500 °C) annealing treatment is a necessity. However, the annealing treatment inevitably leads to the strong phase transformation from TiO2(B) with high lithium ion storage (LIS) capacity to anatase with low LIS one as well as the damage of nanostructures. Herein, we demonstrate a new approach to create TiO2(B)/carbon core/shell nanotubes (C@TBNTs) using a long-chain silane polymethylhydrosiloxane (PMHS) to bind the TBNTs by forming Si-O-Ti bonds. The key feature of this work is that the introduction of PMHS onto TBNTs can afford TBNTs with very high thermal stability at higher than 700 °C and inhibit the phase transformation from TiO2(B) to anatase. Such a high thermal property of PMHS-TBNTs makes them easily coated with highly graphitic carbon shell via CVD process at 700 °C. The as-prepared C@TBNTs deliver outstanding rate capability and electrochemical stability, i.e., reversible capacity above 250 mAh g(-1) at 10 C and a high specific capacity of 479.2 mAh g(-1) after 1000 cycles at 1 C. As far as we know, the LIS performance of our sample is the highest among the previously reported TiO2(B) anode materials.

A colloidoscope of colloid-based porous materials and their uses

Colloids assemble into a variety of bioinspired structures for applications including optics, wetting, sensing, catalysis, and electrodes.

High lithium ion battery performance enhancement by controlled carbon coating of TiO2 hierarchically porous hollow spheres

Hierarchical TiO₂/carbon hollow spheres have been designed and prepared for enhanced lithium storage due to the synergy of the hollow structure, carbon layer and newly formed numerous ∼5 nm Li₂Ti₂O₄ on the surface of the TiO₂ nanocrystals.

In-situ preparation of N-TiO2/graphene nanocomposite and its enhanced photocatalytic hydrogen production by H2S splitting under solar light

Highly monodispersed nitrogen doped TiO2 nanoparticles were successfully deposited on graphene (N-TiO2/Gr) by a facile in-situ wet chemical method for the first time. N-TiO2/Gr has been further used for photocatalytic hydrogen production using a naturally occurring abundant source of energy i.e. solar light. The N-TiO2/Gr nanocomposite composition was optimized by varying the concentrations of dopant nitrogen and graphene (using various concentrations of graphene) for utmost hydrogen production. The structural, optical and morphological aspects of nanocomposites were studied using XRD, UV-DRS, Raman, XPS, FESEM, and TEM. The structural study of the nanocomposite shows existence of anatase N-TiO2. Further, the details of the components present in the composition were confirmed with Raman and XPS. The morphological study shows that very tiny, 7-10 nm sized, N-TiO2 nanoparticles are deposited on the graphene sheet. The optical study reveals a drastic change in absorption edge and consequent total absorption due to nitrogen doping and presence of graphene. Considering the extended absorption edge to the visible region, these nanocomposites were further used as a photocatalyst to transform hazardous H2S waste into eco-friendly hydrogen using solar light. The N-TiO2/Gr nanocomposite with 2% graphene exhibits enhanced photocatalytic stable hydrogen production i.e. ∼5941 μmol h(-1) under solar light irradiation using just 0.2 gm nanocomposite, which is much higher as compared to P25, undoped TiO2 and TiO2/Gr nanocomposite. The enhancement in the photocatalytic activity is attributed to 'N' doping as well as high specific surface area and charge carrier ability of graphene. The recycling of the photocatalyst shows a good stability of the nanocomposites. This work may provide new insights to design other semiconductor deposited graphene novel nanocomposites as a visible light active photocatalyst.