Metal nanowire nonwoven cloth (MNNC) is a metal sheet that has resulted from intertwined metal nanowires 100 nm in diameter with several dozen micrometers of length. Thus, it is a new metallic material having both a flexibility of the metal sheet and a large specific surface area of the nanowires. As an application that utilizes these properties, we propose a high-cyclability electrode for Li storage batteries, in which an active material is deposited or coated on MNNC. The proposed electrode can work without any binders, conductive additives, and current collectors, which might largely improve a practical gravimetric energy density. Huge electrode surfaces provide efficient ion/electron transports, and sufficient interspaces between the respective nanowires accommodate large volume expansions of the active material. To demonstrate these advantages, we have fabricated a NiO-covered nickel nanowire nonwoven cloth (NNNC) by electroless deposition under a magnetic field and annealing in air. The adequately annealed NNNC was shown to be an excellent conversion-type electrode that exhibits a quite high cyclability, 500 mAh/g at 1 C after 300 cycles, compared to that of a composite electrode consisting of NiO nanoparticles. Thus, the present design concept will contribute to a game-changing technology in future lithium ion battery (LIB) electrodes.
Nickel nanowires were synthesized via electroless deposition in an organic solvent (ethylene glycol) under a magnetic field. Deposition behavior of nickel particles and wires were electrochemically investigated at various concentrations of NaOH by an in-situ mixed potential measurement and voltammetry combined with quartz crystal microbalance. Based on the electrochemical investigation, a formation mechanism of nickel wires is proposed. According to the mechanism, nickel wires 100-370 nm in diameter with several dozen m of length were successfully prepared by controlling the reduction rate by varying a concentration of sodium hydroxide, trisodium citrate, and a nucleating agent, chloroplatinic acid.Nanowires of iron group metals (Fe, Co, Ni) and their alloys are attractive materials due to their magnetic properties. 1,2 Numerous synthesis methods of iron group nanowires have been reported. [3][4][5][6][7][8] In their methods, nanowires are formed by electrodeposition using templates such as anodized aluminum oxide 3-5 and polycarbonate membrane. 6-8 The methods with templates have notable advantages that highly-ordered and size-controlled nanowires can be obtained. The template methods, however, require several steps including fabrication and removal of templates in order to obtain bare nanowires. On the other hand, a self-assemble electroless deposition of ferromagnetic nanowires under a magnetic field is a relatively simple synthesis method without any templates. 9 In addition, electroless deposition is a powerful fabrication method with a wide variety of compositions and sizes in a large-scale 10,11 and thus, electroless deposition is suitable for a practical application.We have reported some studies of electrochemical approaches with in-situ mixed potential observation for the synthesis processes of copper, 12,13 cobalt, 14,15 nickel, 16 and Co-Ni alloy 17 nanoparticles, which is effective in thermodynamic oxidation-state control and analysis of the formation process of nanowires as well as nanoparticles. In the present work, the formation process of nickel nanowires via electroless deposition under a magnetic field was electrochemically investigated. In order to control the morphology of nickel deposits, the deposition behavior of nickel was studied by an in-situ mixed potential measurement; it is possible that the reduction rate of Ni(II) species affects the morphology of nickel deposits. Furthermore, the reduction rate and reduction potential of Ni(II) species were investigated by voltammetry combined with quartz crystal microbalance (QCM) as well as the oxidation rate and oxidation potential of hydrazine as a counterpart reaction. ExperimentalThe reaction solutions were prepared using nickel chloride hexahydrate (NiCl 2 Á 6H 2 O) as a source of Ni(II) ions, ethylene glycol (EG) as a solvent, and hydrazine monohydrate (N 2 H 4 Á H 2 O) as a reducing agent. Sodium hydroxide (NaOH) was added as a source of OH À ions. Trisodium citrate dihydrate (Na 3 C 6 H 5 O 7 Á 2H 2 O) and chloroplatinic acid hexahydrate ...
By using phase-field computer simulations, we have investigated the effects of the coherent strain due to the phase separation in the olivine-type LiFePO 4 . In this system, the coherent elastic-strain energy due to the lattice mismatch between LiFePO 4 and FePO 4 phases accompanied by insertion and extraction of Li ions is considered to play a crucial role in the phase separation kinetics during the charge/discharge process. The present phase-field micromechanics simulations reveal several significant features of the LiFePO 4 /FePO 4 system accompanying the coherent strain, such as the retardation of the phase separation, the charge rate dependence, the thermodynamic stability of coherent interfaces between dual phases, etc. Nucleation of the new phase is found to be fundamentally unlikely in terms of the elastic strain energy, except in the vicinity of the surface of the particles, and thus the phase separation would be dominated by the spinodal decomposition process. When the nucleus is present precedently, however, the phase separation can proceed in the mixture mode of the domino cascade and spinodal decomposition processes.
The synthesis process of Co–Ni alloy nanoparticles via electroless deposition in ethylene glycol EG was electrochemically investigated. Insufficient thermodynamic data for organic solvents prevented us from calculating the oxidation–reduction redox potentials of CoII/Co and NiII/Ni redox pairs in organic solvents. In the present work, however, the redox potentials of CoII/Co and NiII/Ni redox pairs in EG were determined by using voltammetry combined with quartz crystal microbalance. In the cyclic voltammograms, the deposition current of cobalt on cobalt substrate was much higher than that of nickel on nickel substrate, which resulted in decreasing particle size with increasing nickel amount. Moreover, it was experimentally clarified that a mixed potential was determined by each partial reaction. Specifically, the hydrazine oxidation reaction was dominant in this reaction system, which is a key to controlling the mixed potential. © 2010 The Electrochemical Society. DOI: 10.1149/1.3352893 All rights reserved. Manuscript submitted December 22, 2009; revised manuscript received February 4, 2010. Published April 8, 2010. Nanoparticles of iron group metals, i.e., Fe, Co, Ni, and their alloys, are attracting great interest because of their magnetic prop-erties. Specifically, iron group alloy nanoparticles have high poten-tial for various applications, such as magnetic field sensors, elec-tronic inductors, magnetic separation, and biomedical applications
Co-Ni nanowires 40-100 nm in diameter with several dozen μm of length were prepared via electroless deposition under a magnetic field. The formation of Co-Ni nanowires was investigated by an in-situ mixed potential measurement and a cyclic voltammetry combined with a quartz crystal microbalance electrode. These electrochemical measurements revealed that the deposition rate of nickel on nickel is lower than that of cobalt on cobalt. Nickel works as an inhibitor in a growth process of Co-Ni alloys. Thus, the thickness of Co-Ni alloy nanowires is drastically reduced by the addition of Ni(II) in solution. The morphology of Co-Ni nanowires is also strongly affected by the magnetization of Co-Ni alloy nanoparticles which are precursors in the formation of nanowires. Both the magnetization and the deposition rate in Co-Ni alloys are the key parameters to control the aspect ratio and surface morphology of nanowires.
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