Mixed bi-material electrodes based on LiMn2O4 and activated carbon for hybrid electrochemical energy storage devices

The performance of mixed bi-material electrodes composed of the battery material, LiMn₂O₄, and the electrochemical capacitor material, activated carbon, for hybrid electrochemical energy storage devices is investigated by galvanostatic charge/discharge and pulsed discharge experiments. Both, a high and a low conductivity lithium-containing electrolyte are used. The specific charge of the bi-material electrode is the linear combination of the specific charges of LiMn₂O₄ and activated carbon according to the electrode composition at low discharge rates. Thus, the specific charge of the bi-material electrode falls between the specific charge of the activated carbon electrode and the LiMn₂O₄ battery electrode. The bi-material electrodes have better rate capability than the LiMn₂O₄ battery electrode. For high current pulsed applications the bi-material electrodes typically outperform both the battery and the capacitor electrode.     

Facile preparation of electrodes based on WO3 nanostructures modified with C and S used as anode materials for Li-ion batteries

An appropriate morphological and structure matrix configuration where lithium ions could insert and de-insert is essential for lithium-ion batteries (LiB). Tungsten oxides (WO₃) are especially attractive materials for this aim. In this research, the effects of the morphology and composition of WO₃ nanostructures on the charge/discharge behavior for Li-ion batteries are methodically examined. On the one hand, nanostructured WO₃ thin film was effectively synthesized by an electrochemical procedure. Then, an annealing treatment at 600°C in air environment for 4 h was carried out. In the second electrode synthesized, a carbon layer was uniformly deposited on WO₃ nanostructures to obtain a WO₃/C electrode. Finally, WO₃/WS₂ electrodes were prepared by means of in situ sulfurization of WO₃ one-step solid-state synthesis using tungsten trioxide (WO₃) and thiourea as precursor material. By using X-ray photoelectron spectroscopy, X-ray diffraction analysis, transmission electron microscopy, Raman spectra, and field-emission scanning electron microscopy, the three electrodes have been morphologically characterized. Electrochemical properties were analyzed by cyclic voltammogram, galvanostatic charge/discharge cycling, and electrochemical impedance spectroscopy. Among all the synthesized samples, WO₃/C nanostructures reveal the best performance as they exhibit the greatest discharge capacity and cycle performance (820 mA h g⁻¹).     

Some factors affecting the electrochemical performances of LaCrO3 as negative electrodes for Ni/MH batteries

Perovskite-type LaCrO₃ used as negative electrode for Ni/MH batteries was prepared by Pechini method and characterized by XRD and SEM. The electrochemical properties under various temperatures and electrolyte concentrations were investigated. The results showed that the discharge capacity of LaCrO₃ electrodes increased with the increase of temperature and electrolyte concentration. Meanwhile, the electrochemical properties of LaCrO₃ electrodes were found to be greatly influenced by the dimension of Ni powders, which served as catalyst in electrodes. EIS was employed to study the phenomena above.     

Fabrication and electrochemical properties of carbon nanotube array electrode for supercapacitors

The multiwalled carbon nanotube (MWNT) array was fabricated by chemical vapor deposition (CVD) in the template of porous alumina from the carbonaceous source of C₂H₂ in the presence of a catalyst of ferric metals. To utilize the external surface other than the inner surface of the carbon nanotubes, 1 mol/L sulfuric acid was applied to remove off the most part of AAO template on the carbon nanotube electrode. The electrochemical performances of the carbon nanotube array electrode were investigated by use of the cyclic voltammetry, galvanostatic charge/discharge and ac impedance methods for its application in supercapacitors. The specific capacitance of 365 F/g of the electrode was achieved with the discharge current density of 210 mA/g in the solution of 1 mol/L H₂SO₄. In addition, the carbon nanotube array electrode was found to have low equivalent series resistance (ESR) and good cycling stability.     

Improvement of electrochemical and thermal stability of LiFePO4@C batteries by depositing amorphous silicon film

Amorphous silicon (α-Si) films are deposited on LiFePO₄@C electrode by using vacuum thermal evaporation deposition technique and the effect of α-Si film on electrochemical performance of LiFePO₄@C cells is investigated systematically by the charge–discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. The results reveal that the present of α-Si film on electrode surface could remarkably improve the electrochemical performance at high charge/discharge rate, especially at elevated temperature. This enhancement may be attributed to the amelioration of the electrochemical dynamics on the electrode/electrolyte interface resulting from the beneficial effects of α-Si film, which might significantly suppress the rise of both of the surface film resistance and charge transfer resistance.     

Study of the electrochemical hydrogen storage properties of the proton-conductive perovskite-type oxide LaCrO3 as negative electrode for Ni/MH batteries

LaCrO₃ was prepared by glycine combustion method and investigated as negative electrode for Ni/MH batteries. The structures of the as-calcined powder and the 20th charge-discharge cycle sample were characterized by XRD. The electrochemical experimental results demonstrated that the LaCrO₃ electrode showed excellent electrochemical reversibility and considerably high charge-discharge capacity at various temperatures. Except for the charge-discharge cycle at 298 K, the discharge capacities of LaCrO₃ electrode keep steady at 107.1 mA h g⁻¹and 285 mA h g⁻¹ at 313 K and 333 K after 5 cycles, respectively.     

Structural and electrochemical properties of mixed calcium-zinc spinel ferrites nanoparticles

In the current work, we provide the electrochemical (EC) characteristics and considerable size of Ca-doped ZnFe₂O₄ nanoparticles. Mixed transition metal oxides are widely used as excellent electrode materials in superior supercapacitors because of their superior capacitance, low cost, and environmental friendliness. The prepared nanoparticles were characterized by X-ray diffraction (XRD), Field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and EC methods. The results exhibited that the as-synthesized nanoparticles had a cubic spinel crystal structure and efficient EC properties. The EC properties of the prepared electrodes were explored by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) studies. The Ca_0.1Zn_0.9Fe₂O₄ electrode demonstrated a specific capacitance (SC) ～208 Fg^-1 at a 2 mV/s scan rate due to significant morphological behavior. Therefore may be the prepared materials are the finest electrodes for supercapacitor applications.     

Comparison of Pore Structures of Cellulose-Based Activated Carbon Fibers and Their Applications for Electrode Materials

This study presents the first investigation of cellulose-based activated carbon fibers (RACFs) prepared as electrode materials for the electric double-layer capacitor (EDLC) in lieu of activated carbon, to determine its efficacy as a low-cost, environmentally friendly enhancement alternative to nanocarbon materials. The RACFs were prepared by steam activation and their textural properties were studied by Brunauer–Emmett–Teller and non-localized density functional theory equations with N₂/77K adsorption isotherms. The crystallite structure of the RACFs was observed by X-ray diffraction. The RACFs were applied as an electrode material for an EDLC and compared with commercial activated carbon (YP-50F). The electrochemical performance of the EDLC was analyzed using galvanostatic charge/discharge curves, cyclic voltammetry, and electrochemical impedance spectroscopy. The results show that the texture properties of the activated carbon fibers were influenced by the activation time. Crucially, the specific surface area, total pore volume, and mesopore volume ratio of the RACF with a 70-min activation time (RACF-70) were 2150 m²/g, 1.03 cm³/g and 31.1%, respectively. Further, electrochemical performance analysis found that the specific capacitance of RACF-70 increased from 82.6 to 103.6 F/g (at 2 mA/cm²). The overall high specific capacitance and low resistance of the RACFs were probably influenced by the pore structure that developed outstanding impedance properties. The results of this work demonstrate that RACFs have promising application value as performance enhancing EDLC electrode materials.     

Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

High methanol oxidation activity of electrocatalysts supported by directly grown nitrogen-containing carbon nanotubes on carbon cloth

The microstructure and electrochemical activity of the Pt-Ru supported by nitrogen-containing carbon nanotubes (CN_x NTs) directly grown on the carbon cloth have been investigated. The CN_x NTs directly grown on the carbon cloth (CN_x NTs-carbon cloth composite electrode) were synthesized using microwave-plasma-enhanced chemical vapour deposition first and then use as the template to support the Pt-Ru nanoclusters subsequently sputtered on. The ferricyanide/ferrocyanide redox reaction in cyclic voltammetry (CV) measurements showed a faster electron transfer on the CN_x NTs-carbon cloth composite electrode than the one with carbon cloth alone. Comparing their methanol oxidation abilities, it is found that the Pt-Ru nanoclusters supported by the CN_x NTs-carbon cloth composite electrode have considerably higher electrocatalytic activity than the carbon cloth counterpart. This result suggests high performance of the CN_x NTs-carbon cloth composite electrode, and demonstrates its suitability for direct methanol fuel cell applications.     

A study on the cycle performance of lithium secondary batteries using lithium nickel-cobalt composite oxide and graphite/coke hybrid carbon

10 Wh-class (30650 type) lithium secondary batteries were fabricated using LiNi_0.7Co_0.3O₂ as the positive electrode material and graphite/coke hybrid carbon as the negative electrode material. In our previous work, we found that LiNi_0.7Co_0.3O₂ and graphite/coke hybrid carbon each provide a longer cycle life among several candidates (Kida et al., J. Power Sources 94 (2001) 74; Kida et al., in preparation; Kinoshita et al., J. Power Sources 102 (2001) 284). In this study, the cycle performance of cells using both LiNi_0.7Co_0.3O₂ and graphite/coke hybrid carbon was examined and the deterioration factor of the discharge capacity was investigated during charge/discharge tests. We then focused our interest on the negative electrode and analyzed it using ⁷Li nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). After the discharge capacity of the battery deteriorated to 70% of the rated capacity after 2000 cycles, the graphite/coke hybrid carbon showed 91% of initial discharge capacity. When the solid electrolyte interface (SEI) (LiF, Li₂CO₃ and polymers) (E. Peled, J. Electrochem. Soc. 126 (1979) 2047) on the carbon negative electrode became thicker in the charge/discharge cycle test, the impedance was considered to have increased. This suggests that the deterioration of the graphite/coke hybrid carbon material is not so large, but that the production of the SEI on the negative electrode and impedance change of the negative electrode are factors of the capacity fade.     

Electrosynthesis and capacitive performance of polyaniline–polypyrrole composite

The composite of polyaniline and polypyrrole (PPY‐PANI) was prepared by two‐step electrochemical polymerization method. Techniques of scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravity analysis (TG/DTG) measurements were used to characterize the morphology and structure of the composite. The electrochemical properties of the composite were investigated by cyclic voltammetry (CV), galvanostatic charge‐discharge, and electrochemical impedance spectroscopy (EIS). The results indicated that the polyaniline–polypyrrole composite showed better electrochemical capacitive performance than polypyrrole (PPY) and polyaniline (PANI). The specific capacitance of the composite electrode was 523 F/g at a current of 6 mA/cm² in 0.5 M H₂SO₄ electrolyte. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Facile synthesis of a novel Fe3O4-rGO-MoO3 ternary nano-composite for high-performance hybrid energy storage applications

Supercapacitors (SCs) have been considered as inspiring energy storage devices due to the long cycle lifetime and high power densities. However, their energy density is limited due to the low capacitance of cathode materials and inferior cycling stability at practically useable potential windows >1.2 V. In this paper, we demonstrate the synthesis of a novel ternary Fe₃O₄-rGO-MoO₃ nano-composite (FGM) with nanoparticles-like morphology (NPs) by utilizing the fast and facile microwave hydrothermal process. The optimized composition of FGM nanocomposite is characterized by the XPS, EDS, Raman, SEM, TEM and HRTEM techniques. The FGM-NPs supported on the carbon cloth (FGM@CC) electrode is used to investigate the electrochemical charge storage properties in basic potassium hydroxide (KOH) electrolyte. The charge-storage properties of the FGM@CC electrode were studied by the CV, GCD and EIS techniques. The obtained results of FGM@CC electrode in aqueous electrolyte showed excellent electrochemical performance as compared with single metal oxides: maximum specific capacitance of 1666.50 F g⁻¹ (FGM@CC), 1075.26 F g⁻¹ (Fe₃O₄ NPs) and 952.38 F g⁻¹ (MoO₃ NPs) at a current density of 2.5 A g⁻¹. The capacitance retention was 95.01% (FGM@CC), 94.1% (Fe₃O₄ NPs) and 92.5% (MoO₃ NPs) after 5000 cycles. Further, the charge storage mechanism is analyzed in the light of power's law and systematical investigated the capacitive and diffusion controlled based stored charge in FGM@CC electrode. Thus FGM nano-composite showed best performance as the cathode material for the next generation flexible supercapacitors.     

Electrochemical capacitor composed of doped polyaniline and polymer electrolyte membrane

We prepared polyaniline doped with LiPF₆ and HCl, respectively, using chemical methods. The electrode composite was attached to both sides of Al mesh, while the polymer electrolyte mixture was spread on a glass plate. Then, the polyaniline‐based redox supercapacitor was fabricated using two electrodes and a polymer electrolyte membrane. The electrochemical performance of the redox supercapacitor was investigated by using the charge/discharge method, cyclic voltometry, and impedance spectroscopy. The initial specific capacitance was ≈115 F/g and it retained ≈90 F/g even after 5000 cycles. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1300–1304, 2003     

Charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides

The charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides was evaluated by various electrochemical techniques (cyclic voltammety, hydrodynamic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy). The effects of various factors, such as particle size, hydrous state, and structure, on the pseudocapacitive property were characterized. The electric double layer capacitance (C_dl), adsorption related charge (C_ad), and the irreversible redox related charge (C_irr) per unit mass and surface area of electrode material has been estimated and the role of structural water within the material either in micropores or interlayer are discussed.     

Synthesis and characterization of nano-sized calcium zincate powder and its application to Ni–Zn batteries

Nano-sized calcium zincate powders used as active materials for a secondary Zn electrode were prepared by a chemical co-precipitation method. The properties were studied by thermal gravimetric analysis (TGA), micro-Raman spectroscopy and nitrogen adsorption–desorption experiments. The secondary Zn electrodes using chemical co-precipitation calcium zincate powders (CP-ZnCa) and ball-milled calcium zincate powders (BM-ZnCa), were examined and compared. The electrochemical performance of the secondary Zn electrodes was systematically investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the electrochemical properties of the secondary Zn-pasted electrode using CP-ZnCa powders were greatly improved, as compared with conventional secondary ZnO electrodes. The results indicated that secondary Ni-Zn batteries using CP-ZnCa powders exhibited a better charge/discharge property and a longer life-cycle performance, compared with those based on ball-milled ZnO + Ca(OH)₂ (BM-ZnCa) powders.     

Origin of Capacity Fading in Nano-Sized Co3O4 Electrodes: Electrochemical Impedance Spectroscopy Study

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co₃O₄, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co₃O₄ with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co₃O₄ anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.     

A novel EDOT–nonylbithiazole–EDOT based comonomer as an active electrode material for supercapacitor applications

A novel EDOT–nonylbithiazole–EDOT based bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer was synthesized and was electrochemically deposited onto carbon fiber electrode as an active electrode material. An electrochemical impedance study on the prepared electrodes is reported in this paper. Capacitive behavior of the carbon fiber microelectrode/poly(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) system was investigated with cyclic voltammetry (CV) experiments and electrochemical impedance spectroscopy. Variation of capacitance values by scan rate and specific capacitance values at different potentials are presented. Specific capacitance value for a galvanostatically prepared polymer film with a charge of 5 C cm⁻² was obtained about 340 mF cm⁻². Effect of the solvent and the deposition charge on the capacitive behavior of the film was investigated using electrochemical impedance spectroscopy. An equivalent circuit model was proposed and the electrochemical impedance data were fitted to find out numerical values of the proposed components. The galvanostatic charge/discharge characteristic of a film was investigated by chronopotentiometry and the morphology of the films electrodeposited at different deposition charges were monitored using FE-SEM.     

碳球@纳米片状钴镍金属氧化物核壳型复合材料的制备及其电化学性能

以葡萄糖为碳源,采用水热炭化法制备碳球,然后以氯化钴和氯化镍为钴源和镍源,六次甲基四胺为沉淀剂,采用水热法和高温处理合成一种核壳结构的碳球@钴镍金属氧化物纳米复合材料,并研究其作为超级电容器电极材料的储能性能。借助X射线衍射、扫描电镜和低温氮气吸附/脱附等对材料的形貌和结构进行表征。采用循环伏安、恒电流充放电及交流阻抗等对材料的电化学性能进行研究。结果表明：碳球的加入能有效改善钴镍金属氧化物的分散性,同时降低材料的电子转移阻力,进而提高其电化学性能。当电流密度为1A/g时,所得碳球@钴镍金属氧化物核壳型复合材料的比电容为984.8F/g;当电流密度增大10倍（10A/g）时,仍保留86.3%的初始比电容值。当电流密度为15A/g时,经过2000次恒电流充放电后复合材料的比电容量保持率为94.6%,体现出较好的循环稳定性能。     

Hydrothermally synthesized microrods and microballs of NiCo2O4 for supercapacitor application

The microrods and microballs of NiCo₂O₄ are successfully synthesized by the hydrothermal method. The effect of ammonium hydroxide and ammonium fluoride on the surface microstructure is observed. The prepared microrods and microballs of NiCo₂O₄ are analyzed by various analytical tools like powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), with energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties are studied by using cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS), using the workstation Biologic SP-200. The maximum specific capacitance of the NiCo₂O₄ microrods electrode is 1671 F/g. The areal specific capacitance of the NiCo₂O₄ microrods electrode is 284 mF/g. The energy density and power density of microrods of NiCo₂O₄ electrode are 19 Wh/Kg and 282 W/kg, respectively. The equivalent series resistance (Rs) is 0.62 Ω for NiCo₂O₄ microrods.