High capacity and good cycling stability of multi-walled carbon nanotube/SnO2 core-shell structures as anode materials of lithium-ion batteries

The multi-walled carbon nanotube/SnO₂ core-shell structures were fabricated by a wet chemical route. The electrochemical performance of the core-shell structures as anode materials of lithium-ion batteries was investigated. The initial discharge capacity and reversible capacity are up to 1472.7 and 1020.5 mAh g⁻¹, respectively. Moreover, the reversible capacity still remains above 720 mAh g⁻¹ over 35 cycles, and the capacity fading is only 0.8% per cycle. Such high capacities and good cyclability are attributed to SnO₂ network structures, excellent mechanical property and good electrical conductivity of the multi-walled carbon nanotubes.     

Synthesis of polycrystalline SnO2 nanotubes on carbon nanotube template for anode material of lithium-ion battery

Polycrystalline tin oxide nanotubes have been prepared by a layer-by-layer technique on carbon nanotubes template. Firstly, the surface of carbon nanotubes was modified by polyelectrolyte. Then, a uniform layer of tin oxide nanoparticles was formed on the positive charged surface of carbon nanotubes via a redox process. At last, the polycrystalline tin oxide nanotubes were synthesized after calcination at 650 °C in air for 3 h. The as-synthesized polycrystalline nanotubes with large surface area exhibit finer lithium storage capacity and cycling performance, which shows the potentially interesting application in lithium-ion battery.     

Preparation of graphene/TiO2 anode materials for lithium-ion batteries by a novel precipitation method

This paper reports a large-scale production route for graphene/TiO₂ nanocomposites using water-based in situ precipitation method. In this method, freshly prepared graphene oxides/TiO₂ obtained by precipitating Ti(SO₄)₂ with NH₃H₂O was subjected to heat treatment in the presence of N₂, which resulted in the formation of graphene/TiO₂ nanocomposites. Graphene/TiO₂ composites prepared by our method were found to be suitable as anode materials for lithium ion batteries because of its stable cycling performance and high capacity.     

Nano-sized Li-Fe composite oxide prepared by a self-catalytic reverse atom transfer radical polymerization approach as an anode material for lithium-ion batteries

A novel Self-catalytic Reverse Atom Transfer Radical Polymerization (RATRP) approach that can provide the radical initiator and the catalyst by the system itself is used to synthesize a nano-sized Li-Fe composite oxide powder in large scale. Its crystalline structure and morphology have been characterized by X-ray diffraction and scanning electron microscopy. The results reveal that the composite is composed of nano-sized LiFeO₂ and Fe₃O₄. Its electrochemical properties are evaluated by charge/discharge measurements. The results show that the Li-Fe composite oxide is an excellent anode material for lithium-ion batteries with good cycling performance (1249 mAh g⁻¹ at 100th cycle) and outstanding rate capability (967 mAh g⁻¹ at 5 C). Such a self-catalytic RATRP approach provides a way to synthesize nano-sized iron oxide-based anode materials industrially with preferable electrochemical performance and can also be applied in other polymer-related area.     

Preparation and ethanol sensing properties of the superstructure SnO2/ZnO composite via alcohol-assisted hydrothermal route

Self-assembled superstructure of SnO₂/ZnO composite was synthesized by using alcohol-assisted hydrothermal method gas sensing properties of the material were investigated by using a static test system. The structure and morphology of the products were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM). The diameter of the SnO₂ nanorods was about 40 nm with a length of about 300 nm, SnO₂ nanorods and ZnO nanosheets interconnect each other to form a superstructure. The gas sensing properties of superstructure SnO₂/ZnO composite with different content of ZnO were investigated. Furthermore, the superstructure SnO₂/ZnO composite sensor is characterized at different operating temperatures and its long-term stability in response to ethanol vapor is tested over a period of 3 months.     

Synthesis and characterization of carbon-coated Fe3O4 nanoflakes as anode material for lithium-ion batteries

The carbon-coated Fe₃O₄ nanoflakes were synthesized by partial reduction of monodispersed hematite (Fe₂O₃) nanoflakes with carbon coating. The carbon-coated Fe₃O₄ nanoflakes were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and galvanostatic charge/discharge measurements. It has been demonstrated that Fe₂O₃ can be completely converted to Fe₃O₄ during the reduction process and carbon can be successfully coated on the surface of Fe₃O₄ nanoflakes, forming a conductive matrix. As anode material for lithium-ion batteries, the carbon-coated Fe₃O₄ nanoflakes exhibit a large reversible capacity up to 740 mAh g⁻¹ with significantly improved cycling stability and rate capability compared to the bare Fe₂O₃ nanoflakes. The superior electrochemical performance of the carbon-coated Fe₃O₄ nanoflakes can be attributed to the synthetic effects between small particle size and highly conductive carbon matrix.     

Preparation of Mn2SnO4 nanoparticles as the anode material for lithium secondary battery

The ultrafine Mn₂SnO₄ nanoparticles with diameters of 5-10 nm have been prepared by thermal decomposition of precursor MnSn(OH)₆. The MnSn(OH)₆ nanoparticles precursor was synthesized by a hydrothermal microemulsion method. X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and electron diffraction have been employed to characterize the crystal structures and morphologies of the as-prepared samples. High-resolution transmission electron microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The thermal characterization was studied by differential thermal analysis and thermogravimetry analysis measurements. Electrochemical test showed that the Mn₂SnO₄ nanoparticles exhibited a high initial charge-discharge capacity of 1320 mAh/g.     

Quasi-cube ZnFe2O4 nanocrystals: Hydrothermal synthesis and photocatalytic activity with TiO2 (Degussa P25) as nanocomposite

The fabrication and photocatalytic application of zinc ferrite nanocrystals were reported. Quasi-cube ZnFe₂O₄ nanocrystals with typical small sizes of 5-15 nm were successfully synthesized by a facile hydrothermal approach. ZnFe₂O₄/P25 nanocomposite was prepared by physically grinding the ZnFe₂O₄ nanocrystals with TiO₂ (commercial Degussa P25) at ambient temperature, and it exhibited excellent photocatalytic activity for the mineralization of Rhodamine B. UV-vis measurement and photocatalytic test results showed that ZnFe₂O₄ nanocrystals exhibited effective band-gap coupling to P25 nanopowders by simply physical grinding without any surface modification or high-energy balling, which is usually adopted in conventional mixture process. This phenomenon can be attributed to the high surface activities of the as-obtained tiny ZnFe₂O₄ nanocrystals and commercial P25 nanoparticles. It may imply that the mixing process of composite materials would be simplified by further lowering the grain sizes of their component particles.     

Facile synthesis of α-MnO2 nanostructures for supercapacitors

Various α-MnO₂ nanostructures have been successfully synthesized by a simple hydrothermal method based on the redox reactions between the MnO₄⁻ and H₂O in mixture containing KMnO₄ and HNO₃. The effect of varying the hydrothermal time to synthesize MnO₂ nanostructures and the forming mechanism of α-MnO₂ nanorods were investigated by using XRD, SEM and TEM. The results revealed an evolvement of morphologies ranging from brushy spherical morphology to nanorods depending upon the hydrothermal time. The surface area of the synthesized nanomaterials varied from 89 to 119 m²/g. Electrochemical properties of the products were evaluated using cyclic voltammetry and galvanostatic charge–discharge studies, and the sample obtained by hydrothermal reaction for 6 h at 120 °C showed maximum capacitance with a value of 152 F/g. In addition, long cycle life and excellent stability of the material were also demonstrated.     

VO2(B) nanospheres: Hydrothermal synthesis and electrochemical properties

Monodisperse VO₂(B) nanospheres with an average size of 100 nm were synthesized by hydrothermal method. Experiments showed that the surfactant octadecyl-amine played an important role during the formation of the nanospheres, and possible mechanism was suggested. Moreover, the potential uses of VO₂ nanospheres were primarily probed as electrodes for lithium-ion batteries.     

Microwave homogeneous synthesis of porous nanowire Co3O4 arrays with high capacity and rate capability for lithium ion batteries

In this paper, an efficient microwave-assisted homogeneous synthesis approach by urea hydrolysis is used to synthesize cobalt-basic-carbonate compounds. The dimensions and morphology of the synthesized precursor compounds are tailored by changes in the incorporated anions (CO₃²⁻ and OH⁻) under different conditions of temperature and time under microwave irradiation. The wire-like cobalt-basic-carbonate compound self-assembles into one-dimensional porous arrays of Co₃O₄ nanowires constructed of interconnected Co₃O₄ nanocrystals along the [1 1 0] axis after thermal decomposition at 350 °C. The textural characteristics of the Co₃O₄ products have strong positive effects on their electrochemical properties as electrode materials in lithium-ion batteries. The obtained porous nanowire Co₃O₄ arrays exhibit excellent capacity retention and rate capability at higher current rates, and their reversible capacity of 600 mAh g⁻¹ can be maintained after 100 cycles at the high current rate of 400 mA g⁻¹.     

A new gel route to synthesize LiCoO2 for lithium-ion batteries

A new synthetic route, i.e. the radiated polymer gel (RPG) method, has been developed and demonstrated for the production of LiCoO₂ powders. The process involved two processes: (1) obtaining a gel by polymerizing a mixed solution of an acrylic monomer and an aqueous solution of lithium and cobalt salts under γ-ray irradiation conditions and (2) obtaining LiCoO₂ powders by drying and calcining the gel. Thermogravimetric analysis (TGA), X-ray diffraction (XRD) and electron scanning microscopy (SEM) were employed to study the reaction process and the structures of the powders. Galvanostatic cell cycling, cyclic voltammetry and ac impedance spectroscopy were used to evaluate the electrochemical properties of the LiCoO₂ powders. It was found that a pure phase of LiCoO₂ can be obtained at the calcination temperature of 800 °C. Both the particle size (micrometer range) and specific charge/discharge capacity of an RPG-LiCoO₂ powder increase with increasing the concentration of its precursor solution.     

CTAB-assisted sol-gel synthesis of Li4Ti5O12 and its performance as anode material for Li-ion batteries

A simple CTAB-assisted sol-gel technique for synthesizing nano-sized Li₄Ti₅O₁₂ with promising electrochemical performance as anode material for lithium ion battery is reported. The structural and morphological properties are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical performance of both samples (with and without CTAB) calcined at 800 °C is evaluated using Swagelok™ cells by galvanostatic charge/discharge cycling at room temperature. The XRD pattern for sample prepared in presence of CTAB and calcined at 800 °C shows high-purity cubic-spinel Li₄Ti₅O₁₂ phase (JCPDS # 26-1198). Nanosized-Li₄Ti₅O₁₂ calcined at 800 °C in presence of CTAB exhibits promising cycling performance with initial discharge capacity of 174 mAh g⁻¹ (∼100% of theoretical capacity) and sustains a capacity value of 164 mAh g⁻¹ beyond 30 cycles. By contrast, the sample prepared in absence of CTAB under identical reaction conditions exhibits initial discharge capacity of 140 mAh g⁻¹ (80% of theoretical capacity) that fades to 110 mAh g⁻¹ after 30 cycles.     

Silicon nanowire array films as advanced anode materials for lithium-ion batteries

Silicon nanowire array films were prepared by metal catalytic etching method and applied as anode materials for rechargeable lithium-ion batteries. The films completely consisted of silicon nanowires that were single crystals. Aluminum films were plated on the backs of the silicon nanowire films and then annealed in an argon atmosphere to improve electronic contact and conduction. In addition to easy preparation and low cost, the silicon nanowire film electrodes exhibited large lithium storage capacity and good cycling performance. The first discharge and charge capacities were 3653 mAh g⁻¹ and 2409 mAh g⁻¹, respectively, at a rate of 150 mA g⁻¹ between 2 and 0.02 V. A stable reversible capacity of about 1000 mAh g⁻¹ was maintained after 30 cycles. The good properties were ascribed to the silicon nanowires which better accommodated the large volume change during lithium-ion intercalation and de-intercalation.     

Preparation of porous SnO2 helical nanotubes and SnO2 sheets

We report a surfactant-free chemical solution route for synthesizing one-dimensional porous SnO₂ helical nanotubes templated by helical carbon nanotubes and two-dimensional SnO₂ sheets templated by graphite sheets. Transmission electron microscopy, X-ray diffraction, cyclic voltammetry, and galvanostatic discharge–charge analysis are used to characterize the SnO₂ samples. The unique nanostructure and morphology make them promising anode materials for lithium-ion batteries. Both the SnO₂ with the tubular structure and the sheet structure shows small initial irreversible capacity loss of 3.2% and 2.2%, respectively. The SnO₂ helical nanotubes show a specific discharge capacity of above 800 mAh g⁻¹ after 10 charge and discharge cycles, exceeding the theoretical capacity of 781 mAh g⁻¹ for SnO₂. The nanotubes remain a specific discharge capacity of 439 mAh g⁻¹ after 30 cycles, which is better than that of SnO₂ sheets (323 mAh g⁻¹).     

Synthesis and characterization of SnO-carbon nanotube composite as anode material for lithium-ion batteries

SnO-carbon nanotube composite was synthesized by a sol-gel method. The electrochemical behavior of the composite using an anode active material in lithium-ion batteries was investigated. It was found that the composite showed enhanced anode performance compared with the unsupported SnO or carbon nanotube (CNT). The capacity fade of the composite electrode was reduced over unsupported SnO or CNT. We attribute the results to the conductivity and ductility of the CNT matrix, and the high dispersion of SnO.     

Synthesis and electrochemical characteristics of Sn-Sb-Ni alloy composite anode for Li-ion rechargeable batteries

Micro-scaled Sn-Sb-Ni alloy composite was synthesized from oxides of Sn, Sb and Ni via carbothermal reduction. The phase composition and electrochemical properties of the Sn-Sb-Ni alloy composite anode material were studied. The prepared alloy composite electrode exhibits a high specific capacity and a good cycling stability. The lithiation capacity was 530 mAh g⁻¹ in the first cycle and maintained at 370-380 mAh g⁻¹ in the following cycles. The good electrochemical performance may be attributed to its relatively large particle size and multi-phase characteristics. The former reason leads to the lower surface impurity and thus the lower initial capacity loss, while the latter results in a stepwise lithiation/delithiation behavior and a smooth volume change of electrode in cycles. The Sn-Sb-Ni alloy composite material shows a good candidate anode material for the rechargeable lithium ion batteries.     

Facile synthesis of mesoporous core-shell TiO2 nanostructures from TiCl3

The present study reports the synthesis and formation process of mesoporous core-shell TiO₂ nanostructures by employing a glucose-assisted solvothermal process using water-ethanol mixture as solvent and subsequent calcination process at 550 °C for 4 h. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption analysis were used to investigate the structural properties of these nanostructures. By optimizing the preparation conditions, especially the contents of water and ethanol in the mixture solvent, mesoporous core-shell TiO₂ nanostructures were obtained. These mesoporous nanostructures have anatase phase and exhibit the superior photocatalytic activity. This synthesis route is facile due to the usage of stable and low-cost Ti precursor such as TiCl₃ and is thus applicable for large-scale production.     

P25/graphene nanocomposites as a high-performance anode material for lithium ion batteries

P25/graphene nanocomposites were successful synthesized in a water-ethanol solvent under hydrothermal conditions. During the process of the reduction of GO into graphene (GR), the P25 nanoparticles were decorated on graphene sheets simultaneously. Moreover, the GR content in the as-synthesized nanocomposites can be easily adjusted by changing the dosage of P25. The interesting P25/GR nanocomposites were found to be a promising anode material for lithium-ion batteries and showed significantly enhanced Li-ion insertion/extraction performance. The optimal weight percentage of GR was found to be 29.9%, which resulted in a high capacity of 282.8 mAh g⁻¹ after 50 cycles at a current rate of 0.5 C. The improved capacity may be attributed to the synergetic effect between graphene sheets and P25 nanoparticles.     

Tetragonal-(Zr,Co)O2 solid solution: Combustion synthesis, thermal stability in air and reduction in H2, H2-CH4 and H2-C2H4 atmospheres

The synthesis of Co²⁺-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr_0.9Co_0.1O_1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H₂, H₂-CH₄ and H₂-C₂H₄ atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H₂-CH₄ produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H₂-C₂H₄ produces 15-30 nm nanofibers.