Evaluation of ZnO nanorod arrays with dandelion-like morphology as negative electrodes for lithium-ion batteries

In this study, ZnO nanorod arrays have been evaluated for the negative electrodes of lithium-ion batteries. The ZnO nanorod arrays with dandelion-like morphology were directly grown on copper substrates by a hydrothermal synthesis process at 80 °C. X-ray diffraction, scanning electron microscopy, galvanostatic discharge-charge, and cyclic voltammetry were employed to characterize the structure and electrochemical property of the arrays. The array electrodes showed a stable capacity over 310 mAh g⁻¹ after 40 cycles, and good capacity retention as the anodes of lithium-ion batteries. It was believed that the unique dandelion-like binary-structure played an important role in the electrochemical performance of the array electrodes. The present finding opens the possibility to fabricate micro/nanometer hierarchical ZnO films that might be applied in lithium-ion batteries.     

Electrochemical performance and morphology evolution of nanosized ZnO as anode material of Ni-Zn batteries

Nanosized ZnO with prismatic form was prepared using homogeneous precipitation process and its electrochemical performance was investigated by the measurements of electrochemical cycle behaviors and passivation polarization curves. The discharge capacity delivered by nanosized ZnO still achieved about 600 mAh/g until the 250th cycle. Nanosized ZnO exhibited higher midpoint discharge voltage, better cycle stability and passivation toleration than commercial ZnO. Furthermore, nanosized ZnO showed the morphology evolution process differed slightly from that of the commercial ZnO, including morphology maintenance, orientation growth and the formation of Zn dendrites. The epitaxial growth, texture growth and crystal growth habit were put forward to illuminate the morphology evolution process.     

A novel high power symmetric ZnO/carbon aerogel composite electrode for electrochemical supercapacitor

We present, for the first time, a new material of symmetric electrochemical supercapacitor in which zinc oxide (ZnO) with carbon aerogel (CA) was used as active material. Physical properties of ZnO/CA composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that ZnO has single hexagonal structure and the grain size increases with increase of ZnO compository. The result of cyclic voltammetry indicates that the specific capacitance of ZnO/CA composite in 6 M KOH electrolyte was approximately 25 F/g at 10 mV/s for 2:1 composition. AC impedance analysis reveals that ZnO with carbon aerogel powder enhanced the conductivity by reducing the internal resistance. Galvanostatic charge/discharge measurements were done at various current densities, namely 25, 50, 75, and 100 mA/cm². It was found that the cells have excellent electrochemical reversibility and capacitive characteristics in KOH electrolyte. The maximum capacitance of the ZnO/CA supercapacitor was 500 F/g at 100 mA/cm². It has been observed that the specific capacitance is constant up to 500 cycles at all current densities, which implies that the dendrite formation was controlled.     

Microstructure and electrochemical properties of electron-beam deposited Sn-Cu thin film anodes for thin film lithium ion batteries

Thin film Sn-Cu anodes with high Cu content were prepared by electron-beam evaporation deposition using Cu substrate as current collector. Annealing, with the condition being determined by DSC, was used to improve the performance of these electrodes. X-ray diffraction (XRD), scanning probe microscopy (SPM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the structure and composition of the Sn-Cu thin film electrodes. Cyclic voltammetry and galvanostatical charge-discharge measurement were carried out to characterize the electrochemical properties of the as-deposited and annealed electrodes. ?-Cu₃Sn intermetallic phase was formed and interface strength between deposited active materials layer and current collector was enhanced by annealing the as-deposited film under suitable condition. The annealed thin film electrode showed good cycleability and had no phase change during cycling. Although large initial capacity loss was found associated with SEI formation due to increase of surface roughness of annealed electrode, a stable discharge capacity near 300 mAh/g with Coulomb efficiency of about 96% was obtained at voltage window of 0.1-2.0 V and a discharge capacity of about 200 mAh/g and Coulomb efficiency of 97% were kept stable up to 30th cycle at a narrower voltage window of 0.2-1.5 V versus Li/Li⁺.     

Porous polythiophene as a cathode material for lithium batteries with high capacity and good cycling stability

Polythiophene (PTh) has been synthesized by chemical oxidative polymerization and used as an active cathode material in lithium batteries. The lithium batteries are characterized by cyclic voltammetry (CV), galvanostatic charge/discharge cycling and electrochemical impedance spectroscopic studies (EIS). The lithium battery with the PTh cathode exhibits a discharge voltage of 3.7 V compared to Li⁺/Li and excellent electrochemical performance. PTh can provide large discharge capacities above 50 mA h g⁻¹ and good cycle stability at a high current density 900 mA g⁻¹. After 500 cycles, the discharge capacity is maintained at 50.6 mA h g⁻¹. PTh is a promising candidate for high-voltage power sources with excellent electrochemical performance.     

Charge/discharge characteristics of sulfur composite cathode materials in rechargeable lithium batteries

The charge and discharge characteristics of lithium batteries with sulfur composite cathodes have been investigated. The sulfur composites showed novel electrochemical characteristics. The analysis of the differential capacity indicated that the discharge process showed two voltage plateaus of 2.10 V and 1.88 V, and the charge process also presented two voltage plateaus of 2.22 V and 2.36 V. The overcharge test showed that the composite cannot be charged over 4.0 V, the voltage always stopped at about 3.9 V during charging, indicating that the composite presented the intrinsic safety for the overcharge of lithium batteries. The overcharge can cause serious safety problem for the conventional Li-ion batteries. The overcharge test also showed that the batteries with sulfur composite were destroyed when the upper cut-off voltage was over 3.6 V. However, the composite presented good reversible capacity after it was deep discharged even to 0 V. It showed stable cycleability and high cycling capacity of 1000 mAh g⁻¹ when cycling between 0.1 V and 3.0 V, indicative of the different characteristic from the conventional oxide cathode materials. The prototype polymer battery with the composite cathode material presented the energy density of 246 Wh kg⁻¹ and 401 Wh L⁻¹.     

Preparation and electrochemistry of NiO/SiNW nanocomposite electrodes for electrochemical capacitors

This paper studies nickel oxide/silicon nanowires (NiO/SiNWs) as composite thin films in electrodes for electrochemical capacitors. The SiNWs as backbones were first prepared by chemical etching, and then the Ni/SiNW composite structure was obtained by electroless plating of nickel onto the surface of the SiNWs. Next, the NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. Once the electrodes were constructed, the electrochemical behavior of these electrodes was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In 2 M KOH solution, the electrode material was found to have novel capacitive characteristics. Finally, when the NiO/SiNW composites were annealed at 400 °C, the maximum specific capacitance value was found to be as high as 681 F g⁻¹ (or 183 F cm⁻³), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. This study demonstrated that NiO/SiNW composites were the optimal electrode choice for electrochemical capacitors.     

1-Alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids as highly safe electrolyte for Li/LiFePO4 battery

Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO₄ battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li⁺/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO₄ cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO₄ battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g⁻¹, which the value is near to theoretical specific capacity (170 mAh g⁻¹). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g⁻¹) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g⁻¹ when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future.     

Synthesis and magnetic properties of Cu-doped ZnO nanowire arrays

Arrays of Cu-doped ZnO nanowires were successfully fabricated by electrodeposition of Zn²⁺ and Cu²⁺ into anodic aluminum oxide template and post-oxidation annealing in air atmosphere. The transmission electron microscopy result shows that the nanowires are uniform, about 100 nm in diameter and with the aspect ratio of up to 40. Selected area electron diffraction and X-ray diffraction results indicate that the nanowires are in hexagonal wurtzite structure. Magnetization measurements show that the Zn_1−xCu_xO (x = 0.07 and 0.11) nanowires exhibit room-temperature ferromagnetism and the enhancement of the ferromagnetism is revealed for the Zn_0.93Cu_0.07O nanowires annealed in vacuum.     

Electrochemical properties of LiNiO2 cathode after TiO2 or ZnO addition

LiNiO₂ was prepared by solid state reaction, and LiNiO₂ was mixed with 1-, 2-, or 5 wt% TiO₂ or ZnO for the preparation of cathodes for a lithium ion battery. The electrochemical properties of the cathodes were investigated and the effects of the addition of TiO₂ or ZnO were discussed. The voltage vs. capacity curves for charge and discharge at different numbers of cycles for LiNiO₂, 2 wt% TiO₂-added LiNiO₂, and 2 wt% ZnO₂-added LiNiO₂ showed that in all the samples the first discharge capacity is much smaller than the first charge capacity. The addition of TiO₂ or ZnO decreased the discharge capacities, but improved the cycling performance. The discharge capacities of LiNiO₂ and 2 wt% TiO₂-added LiNiO₂ decreased as the number of cycles increased. However, the discharge capacity of 2 wt% ZnO-added LiNiO₂ increased overall as the number of cycles increased. The −dx/|dV| vs. voltage curves for the 1st and 2nd cycles of 0, 1-, 2-, or 5 wt% TiO₂ or ZnO-added LiNiO₂ showed that all the samples underwent four phase transitions during charging and discharging.     

Novel synthesis and characterization of silicon carbide nanowires on graphite flakes

Silicon carbide nanowires were synthesized on the surface of graphite by partially reacting with silicon powders in NaF–NaCl based salt at 1150–1400 °C in argon. The effects of temperature and time of heat treatment as well as Si/graphite ratio on synthesis of SiC nanowires were studied. The results showed that the formation of SiC nanowires started at about 1200 °C, and the amounts of SiC nanowires increased in the resultant powders with increasing temperature. Their morphologies were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. It was found that β-SiC nanowires with diameter of 10–50 nm and various lengths grew along their preferred direction perpendicular to (111). The zeta potential of graphite was also increased after coating with silicon carbide nanowires. SiC nanowires that formed on the graphite surface acted as an anti-oxidant to a certain extent, and they protected the inner graphite from oxidation.     

Electrochemical properties of heat-treated polymer-derived SiCN anode for lithium ion batteries

Silicon-carbon-nitrogen material (SiCN) is pyrolyzed from polysilylethylenediamine (PSEDA) derivation, followed by a heat-treating process at 1000 °C in Ar atmosphere. This heat-treated SiCN material has an excellent electrochemical performance as an anode for lithium ion batteries. Charge-discharge cycle measurements show that the heat-treated SiCN material exhibits a high first cycle discharge capacity of 829.0 mAh g⁻¹ and stays between 400 and 370 mAh g⁻¹ after 30 cycles. The discharge capacity remains above 300 mAh g⁻¹ at the high current density of 80 and 160 mA g⁻¹. These values are higher than untreated SiCN and commercial graphite anodes, which indicates that the heat-treating process improves the charge-discharge capacity, cycle stability and high-rate ability of SiCN anode. It is seemed that changes of SiCN structure, the formation of loose nano-holes on material surface and the formation of graphitic carbon phase in heat-treating process contribute to the improvement of electrochemical properties for SiCN anode.     

Study of electrochemical hydrogen charge/discharge properties of FePO4 for application as negative electrodes in hydrogen batteries

We report the electrochemical hydrogen charge/discharge properties of electrodes containing crystalline and amorphous FePO₄ as active material in KOH electrolyte. Crystalline and amorphous FePO₄ were synthesized by an alcohol-assisted precipitation method, and the powders obtained were characterized by X-ray diffraction. X-ray photoelectron spectroscopy is used to investigate the mechanism of hydrogen charge/discharge behavior of FePO₄. The electrochemical hydrogen charge/discharge properties of electrodes containing crystalline and amorphous FePO₄ were investigated for potential application as negative electrodes in rechargeable hydrogen batteries. In galvanostatic discharge/charge mode at 25 °C, the crystalline FePO₄ showed a maximum discharge capacity of 109 mA h g⁻¹, while the amorphous FePO₄ showed a maximum discharge capacity of 81.4 mA h g⁻¹. The electrochemical kinetic properties, exchange current density, and proton diffusivity were calculated using linear polarization measurement and the potential-step method.     

Effect of annealing process on the growth and surface properties of Au–ZnO nanowire films grown by chemical routes

Au–ZnO nanowire films have been synthesized by chemical routes, electrochemical deposition (ECD) and chemical bath deposition (CBD) techniques, on zinc foil followed by annealing in air at 400 °C. X-ray diffraction patterns reveal formation of the ZnO wurtzite structure along with binary phases Au₃Zn and AuZn₃. Scanning electron microscopy shows the presence of ZnO nanowires having several micrometers in length and less than 120 nm in diameter synthesized by ECD and in the range of 70–400 nm using the CBD technique. During the annealing process, different surface morphologies originating from different catalytic effects of Au atoms/layers were observed. In addition, the effect of synthesis routes on crystalline quality and optical properties were studied by Raman and photoluminescence spectrometers indicating varying concentration of defects on the films. The Raman results indicate that Au–ZnO nanowire film prepared by chemical bath deposition route had better crystalline quality.     

Preparation and electrochemical characterization of TiO2 nanowires as an electrode material for lithium-ion batteries

Anatase TiO₂ nanowires containing minor TiO₂(B) phase were prepared by a hydrothermal chemical reaction followed by the post-heat treatment at 400 °C. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, transmission electron microscope, and field-emission scanning electron microscopy. The electrochemical properties were investigated by employing constant current discharge-charge test, cyclic voltammetry, and electrochemical impedance techniques. These nanowires exhibited high rate capacity of 280 mAh g⁻¹ even after 40 cycles, and the coulombic efficiency was approximately 98%, indicating excellent cycling stability and reversibility. The electrochemical impedance spectra showed a stable kinetic process of the electrode reaction. These results indicated that the TiO₂ nanowires have promising application for high energy density lithium-ion batteries.     

Electroless deposition of transparent conducting and 〈0 0 0 1〉-oriented ZnO films from aqueous solutions

Electroless ZnO deposition on a glass substrate from dissolved oxygen-free aqueous solutions containing Zn(NO₃)₂ and dimethylamineborane (DMAB) was examined to yield ZnO films applicable to a transparent conducting oxide (TCO). Concentration of Zn(NO₃)₂ was optimized in terms of crystal growth orientation and surface morphology using XRD and AFM, and that ranging from 0.065 to 0.075 M was found to provide well 〈0 0 0 1〉-oriented dense ZnO films. The polycrystalline ZnO films deposited with Zn(NO₃)₂ concentration of 0.07 M had a preferred 〈0 0 0 1〉 growth orientation and exhibited high visible transparency. Top-view and cross-sectional FE-SEM images revealed that hexagonal columnar ZnO grains with 200 nm in diameter and 290 nm in length grew almost vertically from a glass substrate. Heat treatment at 723 K under a reductive atmosphere was performed to increase the intrinsic carrier concentration in the ZnO film, and Hall effect measurements revealed low electrical resistivity of 4.7 × 10⁻³ Ω cm.     

Electrochemical and ex situ XRD studies of a LiMn1.5Ni0.5O4 high-voltage cathode material

Sub-micro spinel-structured LiMn_1.5Ni_0.5O₄ material was prepared by a spray-drying method. The electrochemical properties of LiMn_1.5Ni_0.5O₄ were investigated using Li ion model cells, Li/LiPF₆ (EC + DMC)/LiMn_1.5Ni_0.5O₄. It was found that the first reversible capacity was about 132 mAh g⁻¹ in the voltage range of 3.60-4.95 V. Ex situ X-ray diffraction (XRD) analysis had been used to characterize the first charge/discharge process of the LiMn_1.5Ni_0.5O₄ electrode. The result suggested that the material configuration maintained invariability. At room temperature, on cycling in high-voltage range (4.50-4.95 V) and low-voltage range (3.60-4.50 V), the discharge capacity of the material was about 100 and 25 mAh g⁻¹, respectively, and the spinel LiMn_1.5Ni_0.5O₄ exhibited good cycle ability in both voltage ranges. However, at high temperature, the material showed different electrochemical characteristics. Excellent electrochemical performance and low material cost make this spinel compound an attractive cathode for advanced lithium ion batteries.     

Electrodeposited PbO2 thin film as positive electrode in PbO2/AC hybrid capacitor

Lead dioxide (PbO₂) thin films were prepared on Ti/SnO₂ substrates by means of electrodeposition method. Galvanostatic technique was applied in PbO₂ film formation process, and the effect of deposition current on morphology and crystalline form of the PbO₂ thin films was studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The energy storage capacity of the prepared PbO₂ electrode was investigated by means of cyclic voltammetry (CV) and charge/discharge cycles, and a rough surface structure PbO₂ film was selected as positive electrode in the construction of PbO₂/AC hybrid capacitor in a 1.28 g cm⁻³ H₂SO₄ solution. The electrochemical performance was determined by charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results showed that the PbO₂/AC hybrid capacitor exhibited high capacitance, good cycling stability and long cycle life. In the voltage range of 1.8-0.8 V during discharge process, considering the weight of all components of the hybrid capacitor, including the two electrodes, current collectors, H₂SO₄ electrolyte and separator, the specific energy and power of the device were 11.7 Wh kg⁻¹ and 22 W kg⁻¹ at 0.75 mA cm⁻², and 7.8 Wh kg⁻¹ and 258 W kg⁻¹ at 10 mA cm⁻² discharge currents, respectively. The capacity retains 83% of its initial value after 3000 deep cycles at the 4 C rate of charge/discharge.     

Oxidation characteristics of nanodot and nanobump on TiN thin films by atomic force microscopy

The electrochemical oxidation characteristics of TiN thin films by atomic force microscopy (AFM) was investigated. The TiN films were produced on silicon substrate by atomic layer chemical vapor deposition (ALCVD). The anodization parameters, such as the anodized voltages, the oxidation times, and how they affected the creation and growth of the oxide nanostructures were explored. The results showed that the height of the TiN oxide dots grew as a result of either the anodization time or the anodized voltage being increased. The oxide growth rate was dependent on the anodized voltage and the resulting electric field strength. Furthermore, the oxide growth rate decreased immediately when the electric field strength reached (2-3) × 10⁷ V/cm rapidly decrease to a growth rate of 0.     

Preparation and electrochemical performance of nanosized Bi compounds-modified ZnO for Zn/Ni secondary cell

Surface-modified ZnO with nanosized Bi compounds was prepared on the basis of the hydrolysis of Bi(NO₃)₃. Transmission electron microscopy images revealed that some nanoparticles with about 40 nm in diameter were modified on ZnO. X-ray diffraction indicated that Bi compounds consisted of Bi₂O₃ and BiO. Electrochemical performances of the surface-modified ZnO were analyzed by charge/discharge cycle test and slow rate cyclic voltammetry (CV). Compared with Bi₂O₃–physically mixed ZnO, nanosized Bi compounds-modified ZnO showed the improved cycle performance, higher discharge capacity and utilization ratio of ZnO. The discharge capacity of the modified ZnO with 9.3 wt.% Bi was the most stable among all tested electrode material and maintained 450 mAh g⁻¹. In comparison with the average utilization ratio (53%) of the physically mixed ZnO, the average utilization ratio of the modified ZnO could reach 80%. The improvement of electrochemical performance resulted from the fact that surface modification with Bi compounds slowed dissolution of ZnO in the electrolyte and maintained the electrochemical activity of ZnO. Cyclic voltammograms clearly illuminated that the modifying agent could decrease polarization, maintain the electrochemical activity, and enhance the discharge capacity of ZnO.