[Show abstract][Hide abstract] ABSTRACT: Porous AgPd-Pd composite nanotubes (NTs) are used as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium-oxygen batteries. The porous NT structure can facilitate rapid O2 and electrolyte diffusion through the NTs and provide abundant catalytic sites, forming a continuous conductive network throughout the entire energy conversion process, with excellent cycling performance.
[Show abstract][Hide abstract] ABSTRACT: Conductive polypyrrole (PPy)-coated LiNi0.5Mn1.5O4 (LNMO) composites are applied as cathode materials in Li-ion batteries, and their electrochemical properties are explored at both room and elevated temperature. The morphology, phase evolution, and chemical properties of the as-prepared samples are analyzed by means of X-ray powder diffraction, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning and transmission electron microscopy techniques. The composite with 5 wt% polypyrrole coating shows a discharge capacity retention of 92% after 300 cycles and better rate capability than the bare LNMO electrode in the potential range of 3.5-4.9 V vs. Li/Li+ at room temperature. At the elevated temperature, the cycling performance of the electrode made from LNMO-5 wt% PPy is also remarkably stable (91% capacity retention after 100 cycles). It is revealed that the polypyrrole coating can suppress the dissolution of manganese in the electrolyte which occurs during cycling. The charge transfer resistance of the composite electrode is much lower than that of the bare LNMO electrode after cycling, indicating that the polypyrrole coating significantly increases the electrical conductivity of the LNMO electrode. Polypyrrole can also work as an effective protective layer to suppress the electrolyte decomposition arising from undesirable reactions between the cathode electrode and electrolyte on the surface of the active material at elevated temperature, leading to high coulombic efficiency.
Journal of Materials Chemistry A 01/2015; 3(1):404-411. DOI:10.1039/C4TA04018J · 7.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Monodisperse porous Ni0.5Zn0.5Fe2O4 nanospheres have been successfully synthesized by the solvothermal method. The diameter of the nanospheres can be tuned by controlling the reactant concentration. Lower reactant concentration is favoured for the synthesis of mesoporous Ni0.5Zn0.5Fe2O4 nanospheres with higher surface area. The electrochemical results show that mesoporous Ni0.5Zn0.5Fe2O4 nanospheres exhibit high reversible specific capacity (1110 mAh g−1) for Li storage and high capacity retention, with 700 mAh g−1 retained up to 50 cycles. The excellent electrochemical properties could be attributed to the large surface area and mesoporous structure. The results suggest that Ni0.5Zn0.5Fe2O4 could be a promising high capacity anode material for lithium ion batteries.
[Show abstract][Hide abstract] ABSTRACT: Paper-like free-standing germanium (Ge) and single-walled carbon nanotube (SWCNT) composite anodes were synthesized by the vacuum filtration of Ge/SWCNT composites, which were prepared by a facile aqueous-based method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Electrochemical measurements demonstrate that the Ge/SWCNT composite paper anode with the weight percentage of 32% Ge delivered a specific discharge capacity of 417 mA h g−1 after 40 cycles at a current density of 25 mA g−1, 117% higher than the pure SWCNT paper anode. The SWCNTs not only function as a flexible mechanical support for strain release, but also provide excellent electrically conducting channels, while the nanosized Ge particles contribute to improving the discharge capacity of the paper anode.
[Show abstract][Hide abstract] ABSTRACT: A germanium–graphene nanocomposite material with three-dimensional nanostructures has been synthesized by an efficient one-step, in situ, and aqueous-based method. The electrochemical properties of the germanium–graphene nanocomposite have been evaluated by galvanostatic discharge–charge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Results show that the germanium–graphene nanocomposite has a much more stable cycling performance than that of the pure germanium, with a capacity of about 832 mA h g−1 after 50 cycles. The rate capability is also improved significantly. The superior performance is attributed to the graphene content, which increases the material's conductivity, enlarges the specific surface area, delivers enough sites to allow dispersion of the Ge nanoparticles without excessive agglomeration, and provides void space to buffer the volume change during discharge–charge cycles.
[Show abstract][Hide abstract] ABSTRACT: In this study, LiNi0.5Mn1.5O4 (LNMO) nanoparticles were prepared as a 5 V cathode material via a rheological phase method and annealed at different temperatures: 680 °C, 750 °C, and 820 °C. The sample annealed at 750 °C shows the best performance. A room temperature ionic liquid (RTIL) containing 1 M lithium bis(trifluoromethanesulfonyl) imide (LiNTf2) in N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide (C4mpyrNTf2) was used as novel electrolyte in conjunction with the LNMO cathodes and their electrochemical properties have been investigated. The results show that the LNMO using RTIL as electrolyte has better coulombic efficiency and comparable discharge capacities to those of the cells assembled with standard liquid electrolyte (1 M LiPF6 in ethylene carbonate/diethyl carbonate). Electrochemical impedance spectroscopy shows that the RTIL is much more stable as the electrolyte for LiNi0.5Mn1.5O4 than the conventional electrolyte.
[Show abstract][Hide abstract] ABSTRACT: CuS nanostructured materials, including nanoflakes, microspheres composed of nanoflakes, microflowers, and nanowires have been selectively synthesized by a facile hydrothermal method using CuSO4 and thiourea as precursors under different conditions. The morphology of CuS particles were affected by the following synthetic parameters: temperature, time, surfactant, pH value, solvent, and concentration of the two precursors. The synthesized CuS nanomaterials were characterized by X-ray diffraction, Brunauer-Emmett-Teller N2 adsorption, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The electrochemical tests, including constant current charge-discharge and cyclic voltammetry, show the specific capacities of the different morphologies, as well as their rate capability. The nanowire electrode has near theoretical specific capacity and the best rate capability.
Journal of Nanoscience and Nanotechnology 02/2013; 13(2):1309-16. DOI:10.1166/jnn.2013.5987 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: LiV3O8–polyaniline nanocomposites have been synthesized via chemical oxidative polymerization directed by the anionic surfactant sodium dodecyl benzene sulfate. The polyaniline particles are uniformly coated on the LiV3O8 nanorods. The composite with 12 wt.% polyaniline retains a discharge capacity of 204 mAh g−1 after 100 cycles and had better rate capability (175 mAh g−1 at 2 C and 145 mAh g−1 at 4 C) than the bare LiV3O8 electrode in the potential range of 1.5–4.0 V. The polyaniline coating can buffer the dissolution into the LiPF6 electrode that occurs in LiV3O8 during cycling. The charge transfer resistance of the composite electrode was much lower than that of the bare LiV3O8 electrode, indicating that polyaniline coating significantly increases the electrical conductivity between the LiV3O8 nanorods. Polyaniline is a conductive binder which buffers the dissolution of LiV3O8 into the electrolyte and reduces the contact resistance among nanorods, so performance of the composite is significantly improved.
Journal of Power Sources 12/2012; 220:47–53. DOI:10.1016/j.jpowsour.2012.07.114 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Copper oxide-carbon composite with hollow sphere structure has been synthesized by a one-step spray pyrolysis method and tested as anode material for lithium-ion batteries. Different analytical methods, including X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric analysis, and systematic electrochemical tests were performed. The results demonstrate that the CuO-carbon composite in conjunction with carboxymethyl cellulose (CMC) binder has an excellent electrochemical performance, with a capacity of 577 mAh g(-1) up to 100 cycles. The usage of the water soluble binder, CMC, not only obviously improves the electrochemical performance, but also makes the electrode fabrication process much easier and more environmentally friendly.
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1314-7. DOI:10.1166/jnn.2012.4643 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fe3O4-carbon composite was prepared by the sol-gel method. The crystal structure, morphology, and phases present in the product were investigated by X-ray diffraction and by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy and field-emission SEM. Electrochemical characterization was performed using constant current charge-discharge testing and electrochemical impedance spectroscopy. The Fe3O4/C electrode has high initial columbic efficiency (87%) and outstanding cycling performance (775.3 mAh g(-1) after 90 cycles at a current density of 100 mA g(-1)).
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1246-50. DOI:10.1166/jnn.2012.4644 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Non-toxic, cheap, nanostructured ternary transition metal oxide CuFeO2 was synthesised using a simple sol–gel method at different temperatures. The effects of the processing temperature on the particle size and electrochemical performance of the nanostructured CuFeO2 were investigated. The electrochemical results show that the sample synthesised at 650 °C shows the best cycling performance, retaining a specific capacity of 475 mAh g−1 beyond 100 cycles, with a capacity fading of less than 0.33% per cycle. The electrode also exhibits good rate capability in the range of 0.5C–4C. At the high rate of 4C, the reversible capacity of CuFeO2 is around 170 mAh g−1. It is believed that the ternary transition metal oxide CuFeO2 is quite acceptable compared with other high performance nanostructured anode materials.
Journal of Power Sources 08/2011; 196(16-196):7025-7029. DOI:10.1016/j.jpowsour.2010.09.108 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A tin nanoparticle/polypyrrole (nano-Sn/PPy) composite was prepared by chemically reducing and coating Sn nanoparticles onto the PPy surface. The composite shows a much higher surface area than the pure nano-Sn reference sample, due to the porous higher surface area of PPy and the much smaller size of Sn in the nano-Sn/PPy composite than in the pure tin nanoparticle sample. Poly(vinylidene fluoride) (PVDF) and sodium carboxymethyl cellulose (CMC) were also used as binders, and the electrochemical performance was investigated. The electrochemical results show that both the capacity retention and the rate capability are in the same order of nano-Sn/PPy-CMC > nano-Sn/PPy-PVDF > nano-Sn-CMC > nano-Sn-PVDF. Scanning electronic microscopy (SEM) and electrochemical impedance spectroscopy (EIS) results show that CMC can prevent the formation of cracks in electrodes caused by the big volume changes during the charge-discharge process, and the PPy in the composite can provide a conducting matrix and alleviate the agglomeration of Sn nanoparticles. The present results indicate that the nano-Sn/PPy composite could be suitable for the next generation of anode materials with relatively good capacity retention and rate capability.