Current Charge Discharge Research Articles

The Performance of Fibrous CDC Electrodes in Aqueous and Non-Aqueous Electrolytes

The aim of this study was to investigate the electrochemical behaviour of aqueous electrolytes on thin-layer (20 µm) nanoporous carbide-derived carbon (CDC) composite fibrous directly electrospun electrodes without further carbonisation. There have been previously investigated fibrous electrodes, which are produced by applying different post-treatment processes, however this makes the production of fibrous electrodes more expensive, complex and time consuming. Furthermore, in the present study high specific capacitance was achieved with directly electrospun nanoporous CDC-based fibrous electrodes in different neutral aqueous electrolytes. The benefit of fibrous electrodes is the advanced mechanical properties compared to the existing commercial electrode technologies based on pressure-rolled or slurry-cast powder mix electrodes. Such improved mechanical properties are preferred in more demanding applications, such as in the space industry. Electrospinning technology also allows for larger electrode production capacities without increased production costs. In addition to the influence of aqueous electrolyte chemical composition, the salt concentration effects and cycle stability with respect to organic electrolytes are investigated. Cyclic voltammetry (CV) measurements on electrospun electrodes showed the highest capacitance for asymmetrical cells with an aqueous 1 M NaNO3-H2O electrolyte. High CV capacitance was correlated with constant current charge–discharge (CC) data, for which a specific capacitance of 191 F g−1 for the positively charged electrode and 311 F g−1 for the negatively charged electrode was achieved. The investigation of electrolyte salt concentration on fibrous electrodes revealed the typical capacitance dependence on ionic conductivity with a peak capacitance at medium concentration levels. The cycle-life measurements of selected two-electrode test cells with aqueous and non-aqueous electrolytes revealed good stability of the electrospun electrodes.

Synthesis of Porous Carbon By Hydrothermal Carbonization and Zinc Chloride Activation of Granulated White Sugar for Supercapacitor Application

The increased global energy demand and pollution of environment due to the consumption of fossil fuels require utilization of energy generated from renewable energy sources such as wind, tidal and solar power. As the contribution of these energy resources grows the energy storage systems with high energy densities, efficiencies and long cycle life become increasingly important. Energy storage systems are needed at times of high energy demand by storing energy when in excess. In this regard supercapacitors (SCs) are considered as the most promising energy storage devices due to their high power density, short characteristic time constant, excellent coulombic reversibility (98% or higher), high energy efficiency (92 – 94%), long cycle life (over 106 cycles) and wide operation temperature range [1-3]. Porous carbon materials are the most promising electrode materials for portable SCs due to the high surface area, good electrical conductivity, good chemical stability, low gravimetric density and low cost [4,5]. The electrical energy accumulated in SCs depends on the electrochemically active surface area and, thus, on the porosity and hierarchical porous structure of a carbon material. In addition, the presence of mesopores in porous carbon materials determines the power density of SCs having a strong effect on the rate of mass transfer and adsorption rate of charge carriers inside the hierarchical porous matrix. Therefore, the characteristics of micro- and mesoporous carbon materials (especially the ratio of micropore and mesopore surface areas and pore volumes) have to be optimized to improve further the specific energy and power density of EDLCs [4,5]. The objective of this study was to investigate the applicability limits of carbon material derived from granulated white sugar (GWS carbon) by hydrothermal carbonization (HTC) method combined with subsequent zinc chloride activation step of hydrochar, for SC electrodes. Synthesized GWS carbon material was used as an electrode material in SC cell filled with 1 M triethylmethylammonium tetrafluoroborate (TEMABF4) solution in acetonitrile (AN) or 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (EMImBF4) as the electrolytes. Cyclic voltammetry (CV), constant current charge/discharge (CC), electrochemical impedance spectroscopy (EIS) and constant power discharge (CP) methods were used to study the electrochemical performance of EDLC. The EIS, CV and CC measurement results show that the values of specific capacitance are somewhat higher for EMImBF4 (135 F g-1) electrolyte compared to the TEMABF4 in AN (110 F g-1). The CP test results show that at low constant power values the stored energy is higher for EDLC based on EMImBF4 ionic liquid (48 W h kg-1) compared with EDLC based on TEMABF4 in AN electrolyte (39 W h kg-1). However, the best capacitance retention, shortest relaxation time constant and substantially higher energy density delivered at higher constant power values were established for SC cell in 1 M TEMABF4 solution in AN due to the lower viscosity and higher electrical conductivity compared to the ionic liquid based electrolyte [5]. Acknowledgements This research was supported by the EU through the European Regional Development Fund (Centers of Excellence, 2014-2020.4.01.15-0011 and 3.2.0101–0030, TeRa project SLOKT12026T. Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026) and Institutional Research Grant IUT20–13. This work was partially supported by Estonian Research Council grants PUT1033 and PUT55.

Granulated White Sugar Derived Carbon Material for Energy Storage Application

In recent years, environmentally friendly energy storage devices have gained increasing attention due to the growing requirement of energy storage for sustainable energy applications. Among the various existing energy storage devices, supercapacitors (electrical double layer capacitors (EDLC) and hybrid capacitors (HC)) are considered as the most promising short-term energy storage devices [1]. EDLCs store energy in the electrical double layer, where the adsorption of ions is based mainly on the electrostatic interactions. The unique characteristics of EDLCs allow them to replace or combine with batteries and fuel cells in applications where the high-power pulses are important, such as the different energy recuperation systems and peak power sources, hybrid electric vehicles, wind turbines, digital communication devices, cameras and mobile phones, laptops, etc. [1]. Porous carbon materials are considered to be the most promising electrode materials for portable supercapacitors due to the high surface area, good electrical conductivity, good chemical stability, low gravimetric density and low cost [2]. The electrical charge accumulated in EDLC depends on the electrochemically active surface area and, thus, on the porosity and hierarchical porous structure of a carbon material. In addition, the presence of mesopores in porous carbon materials determines the power density of EDLC having a strong effect on the rate of mass transfer (diffusion and migration) and adsorption rate of charge carriers inside the hierarchical porous matrix. Therefore, the characteristics of micro- and mesoporous carbon materials (especially the ratio of micropore and mesopore surface areas and pore volumes) have to be optimized to improve further the specific energy and power density of EDLCs [1,2]. The objective of this study was to investigate the applicability limits of carbon material derived from granulated white sugar (GWS carbon) by hydrothermal carbonization (HTC) method combined with subsequent zinc chloride activation step of hydrochar, for supercapacitor electrodes. Synthesized GWS carbon material was used as an electrode material in the two-electrode single cells of EDLC filled with 1 M triethylmethylammonium tetrafluoroborate (TEMABF4) solution in acetonitrile (AN) or 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (EMImBF4) as the electrolytes. Cyclic voltammetry (CV), constant current charge/discharge (CC), electrochemical impedance spectroscopy (EIS) and constant power discharge (CP) methods were used to study the electrochemical performance of EDLC. The EIS, CV and CC measurement results show that the values of specific capacitance are somewhat higher for EMImBF4 (135 F g-1) electrolyte compared to the TEMABF4 in AN (110 F g-1). The CP test results show that at low constant power values the stored energy is higher for EDLC based on EMImBF4 ionic liquid (48 W h kg-1) compared with EDLC based on TEMABF4 in AN electrolyte (39 W h kg-1). However, the best capacitance retention and shortest relaxation time constant were established for EDLCs in 1 M TEMABF4 solution in AN due to the lower viscosity and higher electrical conductivity compared to the ionic liquid based electrolytes and EDLC based on 1 M TEMABF4 solution in AN electrolyte delivers substantially higher energy at higher constant power values. Thus, the GWS carbon material synthesized using cheap and abundant GWS as the starting material, show good electrochemical performance in TEMABF4 in AN as well in EMImBF4 ionic liquid and is promising carbon material for the high energy and power density supercapacitor application. Acknowledgements This research was supported by the EU through the European Regional Development Fund (Centers of Excellence, 2014-2020.4.01.15-0011 and 3.2.0101–0030, TeRa project SLOKT12026T. Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026) and Institutional Research Grant IUT20–13. This work was partially supported by Estonian Research Council grants PUT1033 and PUT55.

(Metal-Organic Framework)-Polyaniline sandwich structure composites as novel hybrid electrode materials for high-performance supercapacitor

Carbonized Zn-(Metal-Organic Framework)MOF- polyaniline composites for high performance of supercapacitor have been developed from zinc acetate, 8-Hydroxyquinoline, and aniline via a simple process. The as-synthesized product has been characterized by X-ray powder diffraction (XRD), Scanning electron microscopy(SEM), Fourier transform infrared spectra (FT-IR), Transmission electron microscope (TEM). The electrochemical properties of carbonized Zn-MOF/polyaniline electrode were investigated by current charge–discharge and cyclic voltammetry. The specific capacitance of MOF/PANI has been approach to be as high as 477 F g−1 at a current density of 1 A g−1.

Electrosynthesised Metal (Ni, Fe, Co) Oxide Films on Single-Walled Carbon Nanotube Platforms and Their Supercapacitance in Acidic and Neutral pH Media

The need for alternative energy sources has led to renewed research interests in electrochemical energy storage systems, especially supercapacitors [1]. Carbon materials such as carbon blacks, carbon fibres, cloths and nanotubes [2], have been used as electrode supports in supercapacitors. Carbon nanotubes (CNTs) have attracted attention due to their unique properties such as high surface area and high porosity that lead to high power densities of supercapacitors [2]. In the quest for an alternative sources, researchers have explored the charge storage properties of different metal oxide systems such as anhydrous Co-Ni oxides in alkaline medium, MnO2 in neutral and acidic conditions, NiO in an acidic conditions [3], Co3O4 in an alkaline medium [4], and Fe3O4 in neutral solution (Na2SO4) and in both neutral and alkaline media [5], as an inexpensive alternatives to RuO2. In addition to good supercapacitive behaviour, metal oxides also have the advantage that they can be readily made into thin films. Although, supercapacitive properties of metal oxides on different substrates have been reported, this work represents the first time a comparative study of the supercapacitive properties of three metal (Ni, Fe, Co) oxide nanoparticles electrochemically deposited onto SWCNTs was carried out. In this work, Supercapacitive properties of single-walled carbon nanotubes/metal oxides nanocomposites (SWCNT-MO where M=Ni, Fe, Co) is described. The SWCNT-MO nanocomposites were confirmed with SEM, EDX and XPS techniques. Supercapacitive properties of the modified electrodes in H2SO4 and Na2SO4 electrolytes was investigated using cyclic voltammetry (CV), galvanostatic constant current charge-discharge (CD) and the electrochemical impedance spectroscopy (EIS) techniques. Electrodecorating acid-functionalised SWCNTs with metal (Ni, Fe, Co) oxide nanoparticles leads to significant enhancements on the supercapacitive properties of these materials in acidic and neutral media compared to many other literature reports. SWCNT-NiO nanocomposite modified electrodes gave better supercapacitive performance with a specific capacitance of 186 mFcm-2 (or 928 Fg-1). This value compared quite favourably and even higher than values hitherto reported in several literature.

A Comparative Study on Ag-Doped and Surfactant Assisted MnO2Prepared by Direct and Pulse Current Electrodeposition on Surgical Grade Stainless Steel as High-Performance Supercapacitor

Direct and pulse current electrodeposition techniques were applied for preparation of novel electro-active manganese oxides. The influences of Ag doping and addition of cetyltrimethylammonium bromide (CTAB) on electrochemical properties were discussed. The morphology and structure of the electrodes are studied by different techniques including field emission scanning electron microscopy (FE-SEM), contact angle and X-ray photoelectron spectroscopy (XPS). Electrochemical behavior of the samples are investigated by cyclic voltammetry (CV), constant current charge-discharge (CC), and electrochemical impedance spectroscopy (EIS). The specific capacitances were measured to be 269, 315, 435, 442, 480 and 508 F g-1 for M-g, M-p, MC-g, MC-p, MCA-g and MCA-p (current density = 1 A g-1), respectively. The MCA-p exhibit high specific capacitance, excellent cycling stability (only 7.5% loss after 1000 cycles at 1 A g-1), and high energy densities (71 Wh kg-1). Ag doping and addition of CTAB which provides more active sites for the pseudocapacitive reactions.

MWCNTS/Nickel Oxide Nanocomposite Supercapacitor Made from Two Electrode Coin Type Cells

Studies have shown that carbon nanotubes-metal oxide (CNT/MO) nanocomposite modified electrodes exhibited huge capacitive current in some electrolytes [1-6]. Therefore, it becomes imperative to establish the charge storage properties of these materials as a potential source for energy generation in acidic and neutral medium since most reported work has been conducted in an alkaline environment. In this work, supercapacitive property of synthesised nickel oxides (NiO) nanoparticles integrated with multi-walled carbon nanotubes (MWCNT) in an acidic medium using a two-electrode coin cell type supercapacitor was investigated. Successful formation of the MWCNT-NiO nanocomposite was confirmed with techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDX) and X-ray diffraction spectroscopy (XRD). The supercapacitive behaviour of both the symmetry and the asymmetry MWCNT-NiO based supercapacitor in 1 M H2SO4 and 1 M Na2SO4 electrolytes was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic constant current charge-discharge (CD) techniques. There was a good correlation between the CV and the CD specific capacitance (SC) values for the asymmetry supercapacitor. Asymmetry supercapacitor (MWCNT-NiO|H2SO4|MWCNT) gave the highest SC value of 925.9 mFcm-2 (53.9 F g-1) and energy deliverable efficiency of 101.0±8.1%. High SC values which are higher than most of those reported in literature were obtained. The electrodes demonstrated high stabilities with no significant changes in SC values over 1000 cycles.

Direct growth of urchin-like ZnCo2O4 microspheres assembled from nanowires on nickel foam as high-performance electrodes for supercapacitors

Urchin-like ZnCo2O4 microspheres grown on nickel foam have been successfully prepared by a two-step facile strategy involving hydrothermal method and subsequent thermal annealing treatment. The as-obtained nickel foam supported urchin-like ZnCo2O4 microspheres can be directly used as the electrodes for the supercapacitors. The physical characterizations indicate that the hierarchical urchin-like ZnCo2O4 microspheres are composed of numerous nanowires and have a large specific surface area of 84.8m2g−1, which are beneficial for the electron and ion transport and the increase of electroactive surface areas. In addition, the electrochemical properties of the urchin-like ZnCo2O4 microspheres as binder-free electrode for supercapacitor are studied by cyclic voltammetry, current charge-discharge, electrochemical impedance spectroscopy, and cycle life measurements in 6M KOH electrolyte. The urchin-like ZnCo2O4 microspheres electrode exhibits a high capacitance of 1841.8 Fg−1 at a current density of 1Ag−1 and keeps the capacitance retention about 78.4% at 10Ag−1. After 3000 cycles, the specific capacitance is about 1390.1Fg−1 at a current density of 10Ag−1, and it also shows the excellent cycling stability (95.8%). All the results demonstrate that the urchin-like ZnCo2O4 microspheres supported on nickel foam have great potential as high-performance electrodes for supercapacitors.

Study on performance of PVDF piezoelectric film for the separator in Li-ion rechargeable cell

The properties of piezoelectric PVDF films as separators are studied in NiO/Li electrodes Li-ion power cell. The results show that the PVDF piezoelectric film with excellent insulation is suitable for the environmental energy harvesting application. This is attributable to the compact structure of the piezoelectric PVDF film, and which make it has low leakage current and low charge-discharge current characteristics.

MWCNTs/metal (Ni, Co, Fe) oxide nanocomposite as potential material for supercapacitors application in acidic and neutral media

Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H2SO4) and sodium sulphate (Na2SO4) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF cm−2 (ca 2,119 F g−1) in H2SO4. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.

Electrosynthesised Metal (Ni, Fe, Co) Oxide Films on Single‐Walled Carbon Nanotube Platforms and Their Supercapacitance in Acidic and Neutral pH Media

AbstractSupercapacitive properties of Single‐walled carbon nanotubes/metal oxides nanocomposites (SWCNT‐MO where M=Ni, Fe, Co) have been described. The SWCNT‐MO nanocomposites was confirmed with SEM, EDX and XPS techniques. Supercapacitive properties of the modified electrodes in H2SO4 and Na2SO4 electrolytes was investigated using cyclic voltammetry (CV), galvanostatic constant current charge‐discharge (CD) and the electrochemical impedance spectroscopy (EIS) techniques. SWCNT‐NiO nanocomposite modified electrodes gave better supercapacitive performance with a specific capacitance of 186 mF cm−2 (or 928 F g−1). This value compared quite favourably and even higher than values hitherto reported in several literature.

The Roles of Intermediate Phases of Li-Si Alloy as Anode Materials for Lithium-Ion Batteries

Abstract An ab initio method of the first-principles plane-wave pseudopotentials based on the density functional theory has been used to calculate the physical character and electrochemical performance of various alloy phases in Li-Si alloy. The results show that besides the growth of solid electrolyte interphase (SEI), the formation of Li12Si7 alloy phase also partly leads to the initial irreversible capacity loss. In addition, the pure silicon thin film electrode was prepared by the radio frequency (RF) magnetic sputtering on copper foil collector as anode materials. The structural and electrochemical characteristics of Li-Si alloy were examined using X-ray diffraction (XRD), cyclic voltammogram (CV) and repeatedly constant current charge/discharge (CC). The results show that the first irreversible capacity loss is very large and amorphous structure can accommodate the large volume expansions and improve cyclic performance.

Investigation on Lithiation Mechanism of Interphase Ni<sub>3</sub>Sn<sub>4</sub> Alloy Used as Anode Material for Lithium-Ion Batteries

Sn-based anode materials have poor cycling performance due to mechanical fatigue caused by volume expansion during lithium insertion and extraction processes. In this work, the mechanism of lithium insertion/extraction in the Ni3Sn4 alloy electrode is investigated using the first-principle plane-wave pseudopotential and experimnetal method. The calculated results indicate that the Ni3Sn4 alloy phase has relatively minor expansion ratio and fluctuating electrochemical potential, which the tendency is consistent with the experimental result. On the other hand, the Sn-Ni alloy thin films with different tin content are prepared by electrodepostion on copper as an anode for lithium-ion batteries. The structural and electrochemical characteristics of Sn-Ni alloy are examined using X-ray diffraction (XRD) and repeated constant current charge/discharge (CC). The results show Tthheat Ni3Sn4 alloy phase has best cyclic stability during the lithium insertion and extraction processes.