Composite Thin Film Electrodes Research Articles

Three-dimensional Li 2O–NiO–CoO composite thin-film anode with network structure for lithium-ion batteries

Three-dimensional Li 2O–NiO–CoO composite thin-film electrodes deposited on stainless steel substrates were synthesized by the electrostatic spray deposition (ESD) technique at 240 and 295 °C. The morphology of the composite was investigated by scanning electron microscopy. X-ray diffraction indicated that the as-deposited films are composites of Li 2O, NiO and CoO. The effects of the solvent used to dissolve the starting materials on the morphology and electrochemical performance of the thin-film electrodes were also investigated. It was found that the as-deposited thin-film electrodes exhibited a high reversible capacity (>800 mAh g −1 when cycled between 0.01 and 3 V at a cycling rate of 0.5 C), good capacity retention, and outstanding rate capability. The superior electrochemical performance may have resulted from the combination of the very porous structure and the three-dimensional network of the as-deposited thin-film electrodes, which contributed to a high surface area, favoured lithium-ion diffusion, and formed a stable integral structure. The thin-film electrodes could be promising anodes for use in high power and high energy density lithium-ion batteries.

Preparation and electrochemical performance of activated carbon thin films with polyethylene oxide-salt addition for electrochemical capacitor applications

The effect of polymer–salt addition in the activated carbon electrode for electric double-layer capacitor (EDLC) has been investigated. A series of composite thin film electrode consisting of activated carbon, carbon black, polytetrafluoroethylene and polymer–salt complex (polyethyleneoxide–LiClO4) with an appropriate weight ratio were prepared and examined their performance for EDLCs using 1 mol L−1 LiClO4 in ethylene carbonate:diethylcarbonate electrolyte solution. The electrochemical capacitance performances of these electrodes with different compositions were characterized by cyclic voltammetry, galvanostatic charge–discharge cycling, and AC impedance measurements. By comparison, the best results were obtained with a composite electrode rich in polymer–salt additive (132 F g−1 at 100 mA g−1 of galvanostatic experiment). In general, the polymer–salt-containing electrode had shown improved performance over activated carbon electrodes without polymer–salt at high current density.

Platinum–Glass Composite Electrode for Fuel Cell Applications

Thin-film electrodes for a low-power direct methanol fuel cell (DMFC) were prepared by incorporating carbon-supported Pt nanoparticles (Pt/C) into a silicon dioxide glass matrix. The SiO 2 matrix was prepared via a sol-gel technique where tetraethyl orthosilicate (TEOS) was hydrolyzed by H 2 O in the presence of methanol. The Pt/C was stirred into the sol and the resulting mixture was applied to a glass membrane substrate and cured. The resulting films were ∼ 2 μm thick. Scanning electron microscopy (SEM) images indicate that the Pt/C was well dispersed, forming glass-separated conductive islands with sheet resistances in excess of 5000 Ω/□. The catalyst islands were interconnected into a conductive sheet by electrolessly depositing platinum from an aqueous plating bath. The Pt/C-SiO 2 glass composite thin-film electrodes showed high methanol oxidation peak currents of ∼ 180 mA/cm 2 when immersed in 0.5 M H 2 SO 4 , 0.5 M methanol electrolyte. The composite electrode was also applied to the anode of a 1 cm 2 passive DMFC and compared to an equivalent passive DMFC with a traditional Nafion-based Pt anode electrode with 10 M MeOH at room temperature. The composite electrode DMFC showed a 50 mV higher open-circuit voltage than the Nafion electrode cell, and the current density was also modestly improved.

Net-like SnS/carbon nanocomposite film anode material for lithium ion batteries

SnS particles with sizes of 5.0–6.5 nm were prepared by a facile method. Resorcinol–formaldehyde sol with addition of the as-prepared SnS nanoparticles was spin-coated on a copper foil to prepare net-like SnS/C composite thin-film electrode for lithium ion batteries after carbonization at 650 °C. The SnS/C nanocomposite thin-film electrode showed preferable first coulombic efficiency and excellent cycling stability. The discharge and charge capacities were respectively 542.3 and 531.3 mAh/g after 40 cycles. The attractive electrochemical performances were mainly ascribed to the ultra fine particle, which showed no evident aggregation in high-resolution TEM image, and the effects of 3-dimensional net-like carbon structure, which uniformly surrounded the SnS nanoparticles to guarantee the contact, acted as a buffer matrix to alleviate the volume expansion of Li–Sn alloy and provided enough paths for electrolyte to reach SnS active material during discharge–charge process.

LiCoPO 4-based ternary composite thin-film electrode for lithium secondary battery

Lithium-excessive LiCoPO 4-based thin-film electrodes were fabricated by electrostatic spray deposition (ESD) technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) were used to analyze the structures and Co oxidation state of the electrodes. The electrochemical properties of these electrodes were evaluated by galvanostatic cell cycling. With an excess of lithium in the initial nominal compositions Li 1+ x CoPO 4 ( x = 0–1), a LiCoPO 4–Li 3PO 4–Co 3O 4 ternary composite was obtained after heat treatment. Li 3PO 4 and Co 3O 4 were introduced and homogeneously distributed in the LiCoPO 4 matrix. We have obtained distinct two-step feature of the voltage plateaus at 4.8 and 4.9 V, high specific capacity and excellent cycling performance for this “5 V”-electrode material. The presence of Co 3O 4 in the electrode can enhance its electronic conductivity and increase the capacity, while Li 3PO 4 can act as an electrolyte separation layer and improve the cycling performance of cells with electrolyte LiPF 6 (EC–DEC, 1:1 v/v).

Fabrication and characterization of SnO 2–RuO 2 composite anode thin film for lithium ion batteries

A SnO 2–RuO 2 composite thin film has very high potential for a hybrid of battery and supercapacitor since SnO 2–RuO 2 system might show battery and supercapacitor characteristics simultaneously. A SnO 2–RuO 2 composite thin film prepared by a magnetron direct current (dc) co-sputtering method in order to investigate a feasibility of monolithic thin film hybrid battery. The as-deposited SnO 2–RuO 2 composite thin film showed crystalline peaks in the X-ray diffraction (XRD) patterns. Rutherford backscattering spectrometry (RBS) and Auger electron spectrometry (AES) analysis were conducted to identify the composition of the as-deposited film. The SnO 2–RuO 2 composite thin film as an anode film for secondary battery demonstrated the first discharge capacity of 400 μAh/cm 2 μm. The discharge curve of the SnRuO composite thin film did not exhibit the 0.8–1.0 plateau characteristic of SnO 2. For SnRuO composite thin film electrode, a plateau at around 1.2 V was observed in the first cycle only. A degree of capacity fade of the SnO 2–RuO 2 composite thin film was almost same to that of the SnO 2 thin film, while the capacity of the SnO 2–RuO 2 thin film was larger than that of the pure SnO 2. In the mean time, the SnO 2–RuO 2 composite thin film as an electrode for supercapacitor exhibited a specific capacitance of 62.2 mF/cm 2 μm. These results suggested that the SnO 2–RuO 2 thin film could be used for thin film supercapacitor as well as thin film battery. Furthermore, this composite thin film holds promise for fabrication of monolithic thin film high power hybrid battery based on micro-processes.

Microstructure and Li alloy formation of nano-structured amorphous Si and Si/TiN composite thin film electrodes

Nano-structured silicon-based thin films have been successfully fabricated in amorphous Si and Si/TiN nano-composite forms by pulsed laser deposition method. A direct comparison of the lithium alloying behavior with the microstructure of these two thin films was investigated by measuring the X-ray diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectrometry and electrochemical galvanostatic cycling. The as-deposited Si and Si/TiN composite thin films fabricated at a laser fluence of 2 J/cm 2 were found to be amorphous. The amorphous Si/TiN nano-composite film used as negative electrode exhibited higher capacity and better capacity retention than that of amorphous Si film electrode, which could be attributed to the dispersed Si particles in the nanometer range, forming an amorphous structure of the composite film and the presence of an inactive matrix of TiN.

Electrochemical properties of metal oxides as anode materials for lithium ion batteries

Some oxides have been investigated as alternative materials for Li-ion batteries. In particular, the In2O3 anodic compound, synthesized in our laboratory, and some commercial powders (PbO, PbO2 and Fe2O3) were studied. The morphology of the oxides was analyzed by SEM investigation. The electrochemical characteristics obtained on composite thin-film electrodes based on these materials are here reported, in term of specific capacity and cyclability.

Experimental and theoretical analysis of LiMn 2O 4 cathodes for use in rechargeable lithium batteries by electrochemical impedance spectroscopy (EIS)

A comparative study of the impedance response measured with composite electrodes and thin film electrodes of LiMn 2O 4 was conducted. The electrodes were prepared on different current collectors (i.e. aluminium, carbonised aluminium and gold) and the experiments were run at various state-of-discharge (SOD) and liquid electrolyte compositions. The impedance response was shown to be strongly dependent on the current collector used. It was demonstrated that the high-to-medium frequency semicircle can be attributed to the contact resistance between the current collector and the active electrode material and that the medium-to-low frequency semicircle can be ascribed to the active electrode material. For the analysis, a mathematical model based on a resistance between the current collector and the active electrode material, interfacial-charge transfer coupled to the double-layer charging and solid-phase diffusion was developed. Potential distribution due to porous electrode effects was also considered. Fitting the model to experimental data enabled reasonable values of the exchange-current density, the double-layer capacitance and the solid-phase diffusion coefficient. However, the very low fitted value of the effective conductivity in the liquid phase indicates that this model does not give a satisfying description of the intercalation process of LiMn 2O 4.

Ag·YSZ複合薄膜電極を用いるYSZ酸素センサーの動作特性

An oxygen sensor with a Ag·YSZ (ZrO2-8 mol%Y2O3) composite thin film electrode deposited on a YSZ disk by ion-beam-sputtering (IBS) was developed. Compositions of the thin films tested were Ag-10 mol%YSZ and Ag-30 mol%YSZ. The performance of the oxygen sensors was examined at temperatures between 573 and 673 K. The mechanism of electrode reactions was inferred on the basis of the results obtained by an AC impedance method. The oxygen sensor with the Ag·YSZ composite thin film electrodes showed the Nernstian response in 1.0% oxygen at temperatures higher than 593 K. The lowest temperature for the Nernstian response was lower by 25 K than that reported for the sensor with a Ag thin film electrode. After a change in oxygen concentration, the response time of the sensor with the Ag-10 mol%YSZ electrode was shorter than that with the Ag-30 mol%YSZ electrode.

Electrochemical characterization of various tin-based oxides as negative electrodes for rechargeable lithium batteries

Tin oxide and tin-based composite electrodes are examined in both bulk and thin-film form for prospective use as negative electrodes for lithium rechargeable batteries. For bulk electrodes, tin oxides and Sn–Zn–P–O composite materials are compared by charge–discharge testings. Thin films of oxides and composite thin-film electrodes prepared by heat treatment (temperature and time) are characterized by X-ray diffraction analysis, Auger electron spectroscopy, and scanning electron microscopy. The characteristics of thin films are found to depend on the heat-treatment temperature, which influences the structure, the grain size, and adhesion to the substrate. Capacities higher than 350 mA h g −1 are found for bulk electrodes beyond 20 cycles, and beyond 100 cycles for thin-film electrodes.

Photoelectrochemical Behavior of Bi2S3 Nanoclusters and Nanostructured Thin Films

Quantized semiconductor nanoclusters of Bi2S3 are prepared in acetonitrile by reacting BiI3 with H2S or Na2S. Both preparation methods yield stable colloids with particle diameters of ≤5 nm. Excitation with a 355-nm laser pulse results in transient bleaching in the 400−500-nm region. This process is followed by the formation of S-surf with a difference absorption maximum around 540 nm. This we attribute to the chemical changes associated with the hole-trapping process. A composite thin film electrode comprised of SnO2/Bi2S3 nanocrystallites has been prepared by sequential deposition of SnO2 and Bi2S3 films onto an optically transparent electrode, and its photoelectrochemical behavior has been studied. The thin film is photoactive in the visible and near-IR and exhibits an incident photon to photocurrent efficiency (IPCE) of ∼15% at 400 nm.