Synergistic effects in an AB5–Co material as an anode for a secondary alkaline battery

The AB₅ alloy and Co powders have been mixed at various weight ratios to form AB₅–Co composite electrodes. The discharge properties such as discharge capacity, discharge plateau, and cycling stability are investigated by charge and discharge testing using Arbin battery testing equipment. Synergistic effects in the composite electrodes contribute to significant improvements of the discharge behavior. For instance, the composite AB₅–25%Co electrode shows a high discharge capacity of 395.1 mAh/g, which is significantly higher than that of AB₅ or Co electrode, and good cycling stability. The discharge process is also characterized by electrochemical impedance spectroscopy. Moreover, the electrochemical discharge mechanism is discussed.     

Electrochemical properties of negative SiMox electrodes deposited on a roughened substrate for rechargeable lithium batteries

To replace conventional carbon, silicon has been widely proposed as a next-generation negative electrode (anode) material for lithium-ion batteries. In this study, Si and SiMo_x-alloy deposited by an RF-magnetron sputtering system is investigated by means of X-ray diffraction, ex situ Raman spectroscopy and transmission electron microscopy. Electrochemical tests are conducted and four different Si and SiMo_x-alloy electrodes and their structures and textual properties are characterized with X-ray photoelectron spectroscopy. The surface morphologies of the electrodes are also observed using field-emission scanning electron microscopy. The electrochemical properties of the electrodes are examined through cycling tests and electrochemical impedance spectroscopy. The results show that rough Cu foil and Mo as alloy materials help Si to retain its discharge capacity and overcome volume expansion during charging and discharging. After a few cycles, the Si electrode severely loses capacity, whereas the SiMo_x-alloy electrodes display good cycle retention and high capacity. The SiMo_0.79 electrode gives an initial capacity of 1319 mAh g⁻¹ that decreases to 1180 mAh g⁻¹ after 100 cycles (89.4%).     

Surface layer formed on silicon thin-film electrode in lithium bis(oxalato) borate-based electrolyte

A Si thin-film electrode of 200 nm is prepared using E-beam evaporation and deposition on copper foil. The use of a lithium bis(oxalato) borate (LiBOB)-based electrolyte markedly improves the discharge capacity retention of a Si thin-film electrode/Li half-cell during cycling. The surface layer formed on Si thin-film electrode in ethylene carbonate/diethyl carbonate (3/7) with 1.3 M LiPF₆ or 0.7 M LiBOB is characterized by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopic analysis. The surface morphology of the electrode after cycling is investigated using scanning electron microscopy. The relationship between the physical morphology and the electrochemical performance of Si thin-film electrode is discussed.     

A paste type negative electrode using a MmNi5 based hydrogen storage alloy for a nickel–metal hydride (Ni–MH) battery

Different conducting materials (nickel, copper, cobalt, graphite) were mixed with a MmNi₅ type hydrogen storage alloy, and negative electrodes for a nickel–metal hydride(Ni–MH) rechargeable battery were prepared and examined with respect to the discharge capacity of the electrodes. The change in the discharge capacity of the electrodes with different conducting materials was measured as a function of the number of electrochemical charge and discharge cycles. From the measurements, the electrodes with cobalt and graphite were found to yield much higher discharge capacities than those with nickel or cobalt. From a comparative discharge measurements for an electrode composed of only cobalt powder without the alloy and an electrode with a mixture of cobalt and the alloy, an appreciable contribution of the cobalt surface to the enhancement of charge and discharge capacities was found.     

Electrochemical characterizations of multi-layer and composite silicon-germanium anodes for Li-ion batteries using magnetron sputtering

To improve the electrochemical performance of Si film, we investigate the addition of two film forms of Ge. Si/Ge multi-layered and Si-Ge composite electrodes that are fabricated by magnetron sputtering onto Cu current collector substrates are investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and extended X-ray absorption fine structure (EXAFS) are employed to analyze the structures of the Si-Ge electrodes. When used as an anode electrode for a lithium ion battery, the first discharge capacity of a Si/Ge 150 multi-layer cell with a ratio of Si 15 nm/Ge 3 nm is 2099 mAh g⁻¹ between 1.1 and 0.01 V. A stable reversible capacity of 1559 mAh g⁻¹ is maintained after 100 cycles with a capacity retention rate of 74.25%. Additionally, the Si_0.84Ge_0.16 composite has an initial discharge capacity of 1915 mAh g⁻¹ and a capacity retention of 74.25%. In full cell tests of Si-Ge electrodes, the Si_0.84Ge_0.16/LiCoO₂ cell delivers a specific capacity of approximatly 160 mAh g⁻¹ and a capacity retention of 52.4% after 100 cycles. The results reveal that these two systems of sputtered Si-Ge electrodes can be used as anodes in lithium ion batteries with higher energy densities.     

Sputtered manganese oxide thin film on carbon nanotubes sheet as a flexible and binder‐free electrode for supercapacitors

In this work, flexible carbon nanotubes (CNTs)/manganese oxide (MnO₂) composite electrode was fabricated by direct deposition of MnO₂ nanoparticles on CNTs sheet by RF magnetron sputtering. The surface morphology and microstructure of the CNTs and CNTs/MnO₂ composite electrodes were characterized by X‐ray diffraction (XRD), scanning electron microscope‐energy dispersive spectroscopy (SEM‐EDS), X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was found that 1‐μm thick MnO₂ film covered the surface of CNTs sheet with MnO₂ mass loading of 0.125 mg/cm². CNTs/MnO₂ composite was tested as electrode materials for supercapacitors in sulfate media (1‐M H₂SO₄ and Na₂SO₄) by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The results obtained showed that CNTs/MnO₂ composite electrode displayed good electrochemical performance in 1‐M Na₂SO₄, while the chemical stability of MnO₂ film was highly affected due its dissolution in acidic medium. A specific capacitance of 940 F/g was retained (with a capacitance retention of about 80%) after 3000 GCD cycles. CNTs/MnO₂ all‐solid symmetric supercapacitor using PVA/H₃PO₄ gel electrolyte exhibited an initial specific capacitance 80 F/g and decreased by 25% after 3000 cycles.     

A novel carbon-silicon composite nanofiber prepared via electrospinning as anode material for high energy-density lithium ion batteries

Electrospun carbon-silicon composite nanofiber is employed as anode material for lithium ion batteries. The morphology of composite nanofiber is optimized on the C/Si ratio to make sure well distribution of silicon particles in carbon matrix. The C/Si (77/23, w/w) nanofiber exhibits large reversible capacity up to 1240 mAh g⁻¹ and excellent capacity retention. Ex situ scanning electron microscopy is also conducted to study the morphology change during discharge/charge cycle, and the result reveals that fibrous morphology can effectively prevent the electrode from mechanical failure due to the large volume expansion during lithium insertion in silicon. AC impedance spectroscopy reveals the possible reason of unsatisfactory rate capability of the nanofiber. These results indicate that this novel C/Si composite nanofiber may has some limitations on high power lithium ion batteries, but it can be a very attractive potential anode material for high energy-density lithium-ion batteries.     

Anode properties of Ru-coated Si thick film electrodes prepared by gas-deposition

Thick film electrodes consisting of Ru and Ru-coated Si particles were fabricated by a gas-deposition method and their electrochemical properties of anodes for Li rechargeable battery were evaluated. The discharge capacity of the Ru electrode at 1000th cycle is approximately 400 mAh g⁻¹. The result showed that the electrode reaction is based on the redox reaction of RuO₂ which was formed on the Ru surface during the charge-discharge processes. By coating Si particles with Ru using an electroless deposition technique, we obtained an electrode with remarkable discharge capacity of 570 mAh g⁻¹ at 1000th cycle. The reason for the improvement in the electrode performance appears to result from the fact that the Ru electrode exhibits excellent cycleability itself and the Ru coated on Si reduces the stress generated by the immense volumetric changes occurring in the Si particles.     

An investigation of the origin of the electrochemical hydrogen storage capacities of the ball-milled Co–Si composites

The Co–Si composites with a molar ratio of 2:1 are synthesized by ball-milling method and their potential as negative electrode materials of Ni–MH batteries is investigated. The microstructure, morphology and chemical state of the ball-milled Co–Si composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD patterns show that the ball-milled samples for 10 and 20 h contain Co, Si and Co₂Si phases, and the ball-milled samples for 40 and 60 h are mainly amorphous Co₂Si alloys. In contrast to the high initial discharge capacity (1012 mAh/g) obtained for the sample ball-milled for 10 h, the discharge capacities of the samples ball-milled for 40 and 60 h are very low. It indicates that the hydrogen storage capacity of pure Co₂Si alloy is very low. It is found that the formation of active Co nanoparticles and Si oxidation are responsible for the high values of the initial discharge capacities of the ball-milled samples for 10 and 20 h. However, after the first cycle, the discharge capacities of the composites drop below 300 mAh/g. Based on XRD and cyclic voltammetric results, the remaining discharge capacity is mainly contributed by the conversion reaction of Co/Co(OH)₂.     

Preparation and electrochemical properties of Co–Si3N4 nanocomposites

Cobalt nanoparticles on an amorphous Si₃N₄ matrix were synthesized by direct ball-milling of Co and Si₃N₄ powders for an improvement of their electrochemical performance. The microstructure, morphology and chemical state of the ball-milled Co–Si₃N₄ composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of Co–Si₃N₄ composites was investigated by galvanostatic charge–discharge process and cyclic voltammetry (CV) technique. It is found that metallic Co nanoparticles of 10–20 nm in size are highly dispersed on the amorphous inactive Si₃N₄ matrix after the ball-milling. The composite with a Co/Si molar ratio of 2/1 shows the optimized electrochemical performance, including discharge capacity and cycle stability. The formation of Co nanoparticles with a good reaction activity is responsible for the discharge capacity of the composites. The reversible faradic reaction between Co and β-Co(OH)₂ is dominant for ball-milled Co–Si₃N₄ composite. The surface modification of the hydrogen storage PrMg₁₂–Ni composites using Co–Si₃N₄ composites can enhance the initial discharge capacity based on the hydrogen electrochemical oxidation and Co redox reaction.     

Effects of pretreatment of LM-Ni3.9Co0.6Mn0.3Al0.2 alloy powders in a KOH/NaBH4 solution on the electrode characteristics and inner pressure of nickel-metal-hydride secondary batteries

The discharge capacities of lanthanum-rich mischmetal (LM)-Ni_3.9Co_0.6Mn_0.3Al_0.2 alloy electrodes are significantly degraded by an increase in the C rate. Nevertheless, the discharge capacity of alloy electrodes pretreated with KOH/NaBH₄ is maintained higher than that of raw alloy electrodes, with the difference in discharge capacities between the raw and pretreated alloy electrodes more prominent at higher C rates. The charge retention of the electrodes decreases with increasing rest time. In particular, the charge retention of the pretreated alloy electrode is lower than that of the raw alloy electrode due to the higher self-discharge rate. The overvoltage for hydrogen evolution of the pretreated alloy electrode is superior to that of the raw alloy electrode, particularly at higher temperatures. This phenomenon indicates that the charge efficiency of the electrode was significantly improved by the surface pretreatment, resulting from its high surface catalytic activity. Repeated charge-discharge increases the inner pressure of the battery. Nevertheless, due to its higher charge efficiency and faster recombination rate, the inner pressure of the battery made using the pretreated alloy electrode is much smaller than that of the battery made using a raw alloy electrode.     

Effect of fluoroethylene carbonate additive on interfacial properties of silicon thin-film electrode

A silicon thin-film electrode (thickness = 200 nm) is prepared by E-beam evaporation and deposition on copper foil. The electrochemical performance of a lithium/silicon thin-film cell is investigated in ethylene carbonate/diethyl carbonate/1.3 M LiPF₆ with and without 3 wt.% fluoroethylene carbonate (FEC). The addition of FEC remarkably improves discharge capacity retention and coulombic efficiency. The surface morphology and chemical composition of the solid electrolyte interphase (SEI) formed on the surface of the silicon thin-film electrode after cycling are studied through scanning electron microscopy and X-ray photoelectron spectroscopy analysis. A smoother and more stable SEI layer structure is generated by the introduction of the FEC additive to the electrolyte.     

Effects of particle size and type of conductive additive on the electrode performances of gas atomized AB5-type hydrogen storage alloy

The phase composition, morphology, structure, and state of the surface of gas atomized LaNi_4.5Al_0.5 alloy powders constituting a fine (≤50 μm), a medium (160–316 μm), and a coarse (630–1000 μm) fraction have been investigated. The electrochemical and storage characteristics of electrodes made from these powders with addition of electrolytic copper powder or a carbon composite (1 wt.% carbon nanotubes + 7 wt.% nanosized carbon black) as a conductive additive have been studied. In the work, X-ray diffraction, scanning electron microscopy, electron-probe microanalysis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and several electrochemical methods have been used. It has been established that, in the initial state, the coarse-fraction gas atomized powders show a better kinetics of the hydrogen exchange reactions and higher discharge capacity (∼300 mA h/g). It is shown that electrodes made from the powders of all the fractions have a good high-rate discharge capability. Hydrogen diffusion coefficients during discharge of the electrodes made from the alloy powders of all the fractions and conductive additives have been calculated. It is shown that, for LaNi_4.5Al_0.5 alloy electrodes with the composite carbon additive, the hydrogen diffusion coefficients during discharge computed from data obtained by the electrochemical impedance spectroscopy method agree well with those calculated from cyclic current–voltage curves (2–4 × 10⁻⁹ cm²/s).     

Preparation and electrochemical hydrogen storage properties of Co9S8 alloy coated with cobalt/graphene composite

A facile one-pot reduction process is used to obtain the cobalt/graphene composite (CoRGO). The CoRGO materials exhibit unique reticular globular morphology. Co₉S₈ hydrogen storage alloy is fabricated via mechanical alloying method. Different amounts of CoRGO are coated on the surface of Co₉S₈ alloy by ball milling. The electrochemical characterizations of the composites are conducted in the standard tri-electrode system. Ultimately, the CoRGO coated Co₉S₈ electrode shows preferable performance than the RGO modified alloy (603.6 mAh/g) and original alloy (577.3 mAh/g). As the additive content of CoRGO is 6 wt%, a maximum discharge capacity of 637.5 mAh/g is obtained. Furthermore, the cycle stability and high-rate dischargeability of the electrode are also enhanced. The Co particles in the CoRGO participate in the reversible redox reactions and the graphene provides high conductivity. The CoRGO with distinctive structure and morphology can not only improve the electrocatalytic activity but also increase the specific surface area of Co₉S₈ alloy. The cobalt and graphene species in the CoRGO composite serve a synergistic effect in further facilitating the hydrogen diffusion, expediting the charge transfer in/on the alloy and improving the corrosion resistance, thus enhancing the electrochemical performance and reaction kinetics of Co₉S₈ alloy.     

The influence of some additives on the electrochemical behaviour of sintered nickel electrodes in alkaline electrolyte

Sintered nickel electrodes containing cobalt and cadmium hydroxides as additives were prepared by anodic polarization in 42 wt.% KOH solution of sintered nickel supports impregnated with mixed metal nitrate solutions. The structural and electrochemical characteristics of these electrodes were investigated by scanning electron microscopy, X-ray diffraction, cyclic voltammetry and charge–discharge curves. The addition of Co(OH)₂ and Cd(OH)₂ in active material have been shown to increase the discharge capacity and coulombic efficiency of nickel electrode by improvement of the electrode processes reversibility and by minimizing of the parasitic oxygen evolution reaction.     

Contribution of polyaniline coating to the stability and performance of nickel hydroxide based electroactive materials

This study has been conducted for investigating the contribution of polyaniline (PANI) to the electroactivity of nickel hydroxide (NH) by using a combination of electrochemical, structural and morphological characterization techniques. NH, PANI and nickel hydroxide/PANI composite (NHP) electrodes were produced on nickel foam substrates. Electrodeposition and chemical bath deposition methods were used for the preparation of NH and PANI, respectively. All the electrochemical experiments were conducted in alkaline solutions. NH and PANI were used as reference materials and exhibited properties in accordance with the literature. Namely, for NH electrode capacity decayed by cycling because of the phase transformation from α to β-Ni(OH)₂, and particles growth from 350 to 850 nm. Also, flower-like structure of the as prepared Ni(OH)₂ faded after 2000 cycles. On the other hand, PANI electrode although exhibited a decrease in the conductivity because of its degradation retained its capacity over cycling because of swelling and shrinking that led to an increased surface area. Composite electrode consisting of PANI and NH resulted in an improvement of capacity retention. At the beginning of cycling capacitance of the composite electrode was 0.64 F/cm², capacity decreased to 0.47 F/cm² after 500 cycles then, continuously increased and finally reached to 0.54 F/cm² after 2000 cycles. Presence of PANI in combination with NH, limited the particle growth and contributed to the preservation of flower like structure of NH. Contrary to both NH and PANI electrodes, charge transfer resistance of NHP exhibited a decrease with cycling indicating a synergy between NH and PANI in addition to morphological changes.     

Investigation of solid electrolyte interfacial layer development during continuous cycling using ac impedance spectra and micro-structural analysis

The formation of passivating surface films on the electrodes of a lithium-ion polymer battery was investigated at various cycling state using ac impedance spectroscopy and scanning electron microscopy (SEM). A sealed commercial cell (Sony Co.) with a nominal capacity of 840 mAh was used for the experiment. An equivalent circuit used to model the impedance spectra show that, with continuous cycling there is a relatively large increase in the interfacial impedance and charge transfer resistances after a few hundred charge–discharge cycles. It was observed that the cell capacity decrease with increase cell impedance. SEM analysis on the electrodes shows that during continuous charge–discharge cycling, the deposition of sub-micro-size particles and dissolution of surface films on the graphite surface. This observation is consistent with increase in cell impedance as a function of charge/discharge cycling.     

Preparation of Sn–Co alloy electrode for lithium ion batteries by pulse electrodeposition

Sn–Co alloy films for Li-ion batteries were prepared by pulse electrodeposition on the copper foils as current collectors. Nanocrystalline Sn–Co alloy electrodes produced by using a solution containing cobalt chloride and tin chloride at constant electrodeposition conditions (pulse on-time t_on at 5 ms and pulse off-time t_off at 5 ms) with varying peak current densities, Jp have been investigated. The structures of the electroplated Sn–Co alloy thin films were studied to reveal film morphology current density relationships and the effect of the current density parameters on the electrochemical properties. X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analyzer and Energy-Dispersive X-ray Spectroscopy (EDS) facilities were used for determination the relationships between structure and experimental parameters. Cyclic voltammetry (CV) tests were carried out to reveal reversible reactions between cobalt–tin and lithium. Galvanostatic charge/discharge (GC) measurements were performed in the cells formed by using anode composite materials produced by pulse electro co-deposition. The discharge capacities of these cells were cyclically tested by a battery tester at a constant current in the different voltage ranges between 0.02 V–1.5 V. The results have shown that Sn–Co alloy yielded promising reversible discharge capacities with a satisfactory cycle life for an alternative anode material to apply for the Li-ion batteries.     

Nanostructured electrodes for next generation rechargeable electrochemical devices

Nanostructured intercalating electrodes offer immense potential for significantly enhancing the performance of rechargeable rocking chair (e.g. Li⁺ and Mg²⁺) and asymmetric hybrid batteries. The objective of this work has been to develop a variety of cathode (e.g. V₂O₅, LiMnO₂ and LiFePO₄) and anode (e.g. Li₄Ti₅O₁₂) materials with unique particle characteristics and controlled composition to reap the maximum benefits of nanophase electrodes for rechargeable Li-based batteries. Different processing routes, which were chosen on the basis of the final composition and the desired particle characteristics of electrode materials, were developed to synthesize a variety of electrode materials. Vapor phase processes were used to synthesize nanopowders of V₂O₅ and TiO₂. TiO₂ was the precursor used for producing ultrafine particles of Li₄Ti₅O₁₂. Liquid phase processes were used to synthesize nanostructured LiMn_xM_1−xO₂ and LiFePO₄ powders. It was found that (i) nanostructured V₂O₅ powders with a metastable structure have 30% higher retention capacity than their coarse-grained counterparts, for the same number of cycles; (ii) the specific capacity of nanostructured LiFePO₄ cathodes can be significantly improved by intimately mixing nanoparticles with carbon particles and that cathodes made of LiFePO₄/C composite powder exhibited a specific capacity of ∼145 mAh/g (85% of the theoretical capacity); (iii) nanostructured, layered LiMn_xM_1−xO₂ cathodes demonstrated a discharge capacity of ∼245 mAh/g (86% of the theoretical capacity) at a slow discharge rate; however, the composition and structure of nanoparticles need to be optimized to improve their rate capabilities and (iv) unlike micron-sized (1–10 μm) powders, ultrafine Li₄Ti₅O₁₂ showed exceptional retention capacity at a discharge rate as high as 10 C in Li-test cells.     

Anodic deposition of manganese oxide electrodes with rod-like structures for application as electrochemical capacitors

The electrochemical properties of nanocrystalline manganese oxide electrodes with rod-like structures were investigated to determine the effect of morphology, chemistry and crystal structure on the corresponding electrochemical behavior of manganese electrodes. Manganese oxide electrodes of high porosity composed of 1-1.5 μm diameter rods were electrochemically synthesized by anodic deposition from a dilute solution of Mn(CH₃COO)₂ (manganese acetate) onto Au coated Si substrates without any surfactants, catalysts or templates under galvanostatic control. The morphology of the electrodes depended on the deposition current density, which greatly influenced the electrochemical performance of the capacitor. Electrochemical property and microstructure analyses of the manganese oxide electrodes were conducted using cyclic voltammetry and microstructural techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The synthesized rod-like manganese oxide electrodes at low current densities exhibited a high specific capacitance due to their large surface areas. The largest value obtained was 185 F g⁻¹ for deposits produced at .5 mA cm⁻². Specific capacity retention for all deposits, after 250 charge-discharge cycles in an aqueous solution of 0.5 M Na₂SO₄, was about 75% of the initial capacity.