Charge Discharge Studies Research Articles

Surfactant assisted polyaniline nanofibres—Reduced graphene oxide (SPG) composite as electrode material for supercapacitors with high rate performance

We have synthesized a composite of surfactant assisted polyaniline nanofibres and graphene oxide (SPGO) followed by reduction to prepare surfactant assisted polyaniline nanofibres-reduced graphene oxide (SPG) composite. The performance of the synthesized composite has been compared with the SPGO, PANI and reduced graphene oxide (rGO). The prepared samples have been characterized by Field effect scanning electron microscopy (FESEM), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) techniques. The electrodes prepared from these samples have been tested for their electrochemical performances using cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedence spectroscopy (EIS), in a two electrode configuration. The CV results revealed that the SPG cell has higher voltammetric current as compared to SPGO, PANI and rGO cells leading to better capacitive nature. From charge discharge studies, the SPG cell exhibits maximum specific capacitance of 444Fg−1 at 0.6 Ag−1 with good retention after 2000 charge discharge cycles. The specific energy and power density of the SPG cell is observed to be 13.36Whkg−1 and 1.03kWkg−1, respectively, which is significantly large as compared to SPGO, PANI and rGO cells. The EIS studies showed enhanced rate performance of SPG cell as compared to the rGO and PANI cell which is in agreement with the CV results. These results make it a promising candidate for supercapacitor applications.

SILAR deposited Bi2S3 thin film towards electrochemical supercapacitor

Bi2S3 thin film electrode has been synthesized by simple and low cost successive ionic layer adsorption and reaction (SILAR) method on stainless steel (SS) substrate at room temperature. The formation of interconnected nanoparticles with nanoporous surface morphology has been achieved and which is favourable to the supercapacitor applications. Electrochemical supercapacitive performance of Bi2S3 thin film electrode has been performed through cyclic voltammetry, charge-discharge and stability studies in aqueous Na2SO4 electrolyte. The Bi2S3 thin film electrode exhibits the specific capacitance of 289Fg−1 at 5mVs−1 scan rate in 1M Na2SO4 electrolyte.

Montmorillonite embedded electrospun PVdF–HFP nanocomposite membrane electrolyte for Li-ion capacitors

The electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/montmorillonite nanofibrous composite membranes (esCPMs) were prepared by electrospinning technique using a mixture of different amounts of montmorillonite (0, 3, 5, 7 and 10wt%) into 16wt% of PVDFHFP polymer solution in 7:3wt% of acetone and dimethylacetamide as the solvent. The effect of montmorillonite (MMT) on electrospun PVdF–HFP membrane has been studied by XRD, DSC, TGA and tensile strength analysis. The average diameter of the electrospun nanofibrous composite membrane was about ∼400nm. The physical properties such as porosity, electrolyte uptake and mechanical strength of the electrospun nanofibrous composite membrane were studied in detail. The ionic conductivity and electrochemical stability windows of the electrospun nanofibrous composite membrane containing 1M LiPF6 in EC:DMC (1:1, v/v%) as an electrolyte (esCPME) were studied by AC-impedance and linear sweep voltammetry studies, respectively. It is found that electrospun PVDF–HFP/MMT nanofibrous composite membrane obtained using 5wt% MMT has a higher porosity, electrolyte uptake, ionic conductivity and electrochemical stability window than the other nanofibrous composite membrane systems and are found to be 88.1%, 428%, 2.330×10−3S/cm and 3.1V, respectively. Finally, the charge–discharge studies were carried out by fabricating a prototype Li-ion supercapacitor by sandwiching PVDF–HFP/MMT (5wt%) nanofibrous composite membrane electrolyte in between a carbon anode and LiCo0.2Mn1.8O4 cathode. It showed higher specific discharge capacitance and good compatibility with electrode materials suggesting that the electrospun PVdF–HFP/MMT nanofibrous composite membrane electrolyte could be used as the best candidate for high performance Li-ion capacitors.

Synthesis and electrochemical performance of P2-Na0.67AlxCo1-xO2 (0.0 ≤ × ≤ 0.5) nanopowders for sodium-ion capacitors

Layered P2-Na0.67Al x Co 1-x O2 (0.0 ≤ × ≤ 0.5) nanopowders were prepared by solution combustion process. These nanopowders were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and field emission scanning electron microscopy (FE-SEM) analysis. The electrochemical behaviours of the prepared layered P2-Na0.67Al x Co 1-x O2 nanopowder-based electrodes were investigated by cyclic voltammetry, electrochemical impedances and galvanostatic charge-discharge studies in 1 M Na2SO4 solution. The layered P2-Na0.67Al0.3Co0.7O2 has achieved a high specific capacitance of 260 F g−1 at a constant current density of 1 A g−1. The excellent electrochemical performance of Na0.67Al0.3Co0.7O2 is due to the partial substitution of Al3+ ions for Co3+ ions that leads to decrease in lattice parameter, resulting in the better structural stability during the Na+ ion intercalation/deintercalation reaction process. Moreover, the Na0.67Al0.3Co0.7O2 demonstrates a long cycle life with 80.1 % of its specific capacitance retention even after 5000 continuous charge-discharge process at a constant current density of 1 A g−1.

Metal Organic Frameworks/Ionic Liquid Composites As Electrolytes for Li-Ion Batteries

Metal Organic Frameworks (MOFs), as a novel class of crystalline porous material have gained great attention in the fields of gas storage, separation, drug delivery, catalysis, sensors and so forth. The supramolecular design of MOFs allow a number of organic ligands, with two or more functional groups, to be linked to metal ion coordination centers giving myriad variations and tunable properties in synthesized structures. Metal Organic Frameworks (MOFs) are of great interest due to several unique features and their applications have been extended to the field of Li-ion batteries. Simultaneously, ionic liquids (ILs) are becoming popular in a range of areas including biphasic reaction catalysis, electromechanical actuator membranes and diluents and separation membranes. Many studies have been conducted for the application of MOFs in energy storage devices [1]-[3], but scarcely any investigation was performed to understand the effect of ionic liquid incorporated MOFs in electrochemical storage devices especially batteries. Hence, an attempt has been made by our group with ionic liquid incorporated modified MOFs to serve as a better electrolyte system for Li-ion batteries with increased thermal and electrochemical stability, high ionic conductivity and other electrochemical aspects. Further, dimensionally and morphologically controlled MOFs will be carefully used to ease the ion transport in the electrolyte system by the regulation of ion conductive path. MOF-1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AMImTFSI), synthesized by a facile in-situ electrochemical method [4] was doped with a lithium salt, lithium bis (triflouromethylsulfonyl) imide (LiTFSI) by a modified procedure for electrochemical measurements. Morphological features and crystal size of these matrices were evaluated by TEM (Transmission Electron Microscopy) and XRD measurements. Temperature dependence of ionic conductivity of the MOF/ionic liquid matrix was studied by AC-impedance method. Combination of AC-impedance and DC-polarization method was used to determine the lithium ion transference number of the samples. Electrochemical window of different electrolyte compositions was studied by linear sweep voltammetry. A coin cell was fabricated to study the charge discharge characteristics of the resulting cell. Synthesis of MOF-5/ionic liquid matrix by electrochemical method - MOF was successfully synthesized by a mild in-situ electrochemical method using 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AMImTFSI) as a templating agent employing a modified procedure of reported method [4]. Synthesis of the MOF (AMImTFSI) was achieved by a constant dissolution of Zn2+ ion from Zn anode. The dissolution was carried out by applying a constant direct current (DC) of 0.15A. A titanium electrode was employed as cathode. The electrolyte used in this procedure was a solution containing 0.07 M terephthalic acid and 0.04 M zinc nitrate hexahydrate in DMF. The electrochemical galvanostatic procedure was carried out for 3hrs. A white powder formed during the above mentioned procedure, was filtered and washed with DMF first and then, with chloroform. The sample was then dried in oven at 80 oC to get pure MOF (IL). For further electrochemical analysis, MOF (IL) was doped with lithium salt, LiTFSI. A set of samples were synthesized with varying content of MOF (IL) in ionic liquid system and ionic conductivity was measured by AC-impedance method. Three samples with different weight % of MOF (IL) in AMImTFSI were prepared and temperature dependent ionic conductivity measurements were performed by AC impedance method. All the samples showed linear profiles in Arrhenius plots. As expected the ionic conductivity decreased with increase in wt% of MOF (IL) because of change in state from liquid to gel. Interestingly a decrease in activation energy of ion transport was observed. The ionic conductivities of the samples were calculated by the Vogel-Fulcher-Tammann (VFT) equation, resulting out to be highest for the sample with 10 wt% of MOF (IL) in AMImTFSI i.e. 1.0 x 10-2 Scm-1 at 51 oC . The highest tLi + of 0.31 was observed for 20 wt% MOF (IL) in AMImTFSI. The systems showed a potential window of 5.22-5.55 V. Charge discharge studies were also carried out after fabricating a coin anodic half-cell composed of Si/electrolyte/Li which showed 90% coulombic efficiency in the presence of 30 mL of EC: DC=1:1 in electrolyte. Conclusion Modified MOF with ionic liquid framework was prepared in ionic liquid system by electrochemical method. Measurements of temperature dependence of ionic conductivity using AC impedance showed relatively high ionic conductivity. These encouraging results affirm the prepared modified MOF (IL) to be a prospective electrolyte in energy storage devices.

Electrochemical Properties of LiNi0.85Co0.10Al0.05O2 synthesized By Using AAO(Anodic Aluminum Oxide) Template

Recently, among various cathode materials for lithium batteries, LiCoO2 has been still use on the market due to electrochemical stability. However, LiCoO2 cathode materials have low thermal stability, high cost, low capacity. [1-2] Co and Al co-synthesized materials, Li(Ni,Co,Al)O2, are one of the most applicable materials due to the low cost, thermal stability than LiCoO2. Thus, the battery properties of lithium ion cell with LiNi0.85Co0.10Al0.05O2 cathode are better than LiCoO2. But, LiNi0.85Co0.10Al0.05O2 still show that capacity fading. [3] Anodizing method is an effective means of improving electrochemical performance. To improve the electrochemical properties of cathode material LiNi0.85Co0.10Al0.05O2 for a lithium-ion battery, LiNi0.85Co0.10Al0.05O2 cathode powders were prepared by sol-gel method in AAO template followed by heat treatment. The prepared compounds were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) studies and were subjected to charge-discharge cycling performance studies at different C-rates. Though the SEM, AFM, it was confirm that nano-rod for cathode material was obtained. [4] References [1] T. J. Park, J. B. Lim, and J. T. Son, Bull. Korean Chem. Soc. 2014 , Vol. 35, No. 2 357 [2] Z. R. Chang, X.Z. Yuan and H. Wang, Powder Technology 207 (2011) 396 – 400 [3] H. Kondo, T. Kamiyama and Y. Ukyo, J. Power Sources 174 (2007) 1131–1136 [4] S. B. Yang, C. Kim, B. C. Jang, and J. T. Son, J. Korean Physical Soc. Vol. 67, No.4 728~732 Acknowledgement This study was supported by the granted financial resource from Korea National University of Transportation in 2016, the Ministry of Trade program of the Industry & Energy, Republic of Korea (G02N03620000901) and the Global Excellent Technology Innovation of the Korea Institute of Energy Technology Evaluation and Planning (KETEP).

High Per formance and Flexible Supercapacitors based on Carbonized Bamboo Fibers for Wide Temperature Applications.

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

Enhanced specific capacitance and supercapacitive properties of polyaniline–iron oxide (PANI–Fe2O3) composite electrode material

In the present work we report ferric oxide (α-Fe2O3) and conducting polyaniline–ferric oxide (PANI–Fe2O3) composite thin films prepared using simple electrodeposition technique. The structural and morphological analysis was carried out by X-ray diffraction and scanning electron microscopy. The supercapacitive properties of these films were examined using cyclic voltammetry, charge–discharge studies, and electrochemical impedance spectroscopy in 0.5 M Na2SO4 electrolyte. It is observed that the PANI–Fe2O3 composite electrode delivered higher specific capacitance than individual α-Fe2O3. Also the composite thin film electrode exhibits excellent specific capacitance retention of about 87 % over 1000 CV scan cycles as compared to α-Fe2O3 electrode, which exhibits only 84 % retention capacity.

Electric double-layer capacitors with tea waste derived activated carbon electrodes and plastic crystal based flexible gel polymer electrolytes

We report a novel configuration of symmetrical electric double-layer capacitors (EDLCs) comprising a plastic crystalline succinonitrile (SN) based flexible polymer gel electrolyte, incorporated with sodium trifluoromethane sulfonate (NaTf) immobilised in a host polymer poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP). The cost-effective activated carbon powder possessing a specific surface area (SSA) of ~ 1700 m2g-1 containing a large proportion of meso-porosity has been derived from tea waste to use as supercapacitor electrodes. The high ionic conductivity (~3.6×10-3 S cm-1 at room temperature) and good electrochemical stability render the gel polymer electrolyte film a suitable candidate for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge studies. The performance of the EDLC cell is found to be promising in terms of high values of specific capacitance (~270 F g-1), specific energy (~ 36 Wh kg-1), and power density (~ 33 kW kg-1).

Electrical and electrochemical studies of nanocrystalline mesoporous MgFe2O4 as anode material for lithium battery applications

Nanocrystalline mesoporous spinel magnesium ferrite (MgFe2O4) particles with high surface area were prepared by urea assisted modified citrate combustion process. The prepared sample was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field-emission scanning electron microscope (FE-SEM), BET surface area analyzer and impedance spectroscopy techniques. XRD results confirmed the formation of a single phase of nanocrystalline spinel magnesium ferrite sample. FTIR and Raman spectroscopy (FTIR) results confirmed the structural co-ordination of the magnesium ferrite sample. The spherical shape morphology of the prepared magnesium ferrite particles was confirmed from the FE-SEM images. Specific surface area and porosity of the MgFe2O4 sample were obtained from N2 adsorption–desorption isotherms results. The D.C. and A.C. electrical conductivities of the MgFe2O4 sample as a function of temperature and frequency were investigated by analyzing the measured impedance data. The activation energy for the migration of the carriers in the MgFe2O4 sample was found to be 0.607eV. The dielectric studies revealed that the dielectric constant of the mesoporous MgFe2O4 sample increases with increase in temperature. Further, lithium battery was fabricated using the developed nanocrystalline mesoporous spinel MgFe2O4 as anode material and investigated its electrochemical performance. The charge-discharge studies revealed that the fabricated lithium battery using the developed nanocrystalline mesoporous MgFe2O4 as anode exhibited high capacity and good cycleability in the voltage range 0.005–3V. The results show that the developed nanocrystalline mesoporous spinel magnesium ferrite could be a better anode material for lithium battery applications.

Synthesis, Characterization, and Electrochemical Analysis of the Cobalt Free Composite Cathode Material 0.5Li2MnO3-0.25LiMn2O4-0.25LiNi0.5Mn0.5O2 for Lithium Ion Batteries Applications

ABSTRACTThe inclusion of a spinel structure in the layered-layered composite cathode material is currently explored to enhance the cycling stability and electrochemical properties of lithium ion batteries. Li2MnO3 based composite cathodes are one of the most widely investigated positive electrodes due to their high discharge capacity and rate capability. In our studies, we have synthesized the cobalt-free layered-layered-spinel composite cathode material, 0.5Li2MnO3-0.25LiMn2O4-0.25LiNi0.5Mn0.5O2 (LLNMO), via the sol-gel method. The structure of the composition was characterized using XRD and Raman Spectroscopy in which peaks corresponding to the layered and spinel structures were identified. The morphology along with the elemental analysis were studied with SEM/EDX. The SEM images exhibited agglomerates with particle size in the nano range and the EDX analysis confirmed the presence of manganese, nickel and oxygen in the structure. The electrochemical performance was analyzed by charge/discharge studies (CD) and cyclic voltammetry (CV). The composite cathode material showed high capacity retention and good cycle stability with a coulombic efficiency of 98%. The discussed results demonstrated that LLNMO is a promising cathode material for the next generation of Li-ion batteries.

Caterpillar-like sub-micron LiNi0.5Mn1.5O4 structures with site disorder and excess Mn3+ as high performance cathode material for lithium ion batteries

Caterpillar-like spinel LiNi0.5Mn1.5O4 (LNMO) sub-micron structures with Fd3m space group were synthesised by polymer assisted sol-gel/electrospinning and post heat treatments in air atmosphere. The novel caterpillar structures were composed of 60–100nm sized well sintered and interconnected nano grains as observed by FESEM and TEM studies. The presence of Fd3m structure in the LNMO caterpillars were confirmed using X-Ray Diffraction and Raman spectroscopy studies. The Cyclic Voltammetry and Galvanostatic charge-discharge studies revealed the presence of substantial amount of Mn3+ in LNMO caterpillars. The LNMO caterpillar structures have exhibited high rate capability and excellent capacity retention (118mAh/g at 1C rate) after 100 cycles of charge discharge, when compared with P4332 LNMO sol heated powders (82mAh/g at 1C rate) synthesised in the absence of polymer. The EIS studies revealed low charge transfer resistances in LNMO caterpillars (4 times lower) in comparison to LNMO sol heated powders. The prepared LNMO caterpillar like structures with considerable Mn3+ concentration can be considered as a high performance cathode material for Lithium ion batteries.

Effect of carbon on galvanically deposited cuprous oxide as flexible charge storage electrode

Electroless deposition of cuprous oxide was carried out on Al foil and heat treated at 370°C. Different combination of Carbon/Cuprous oxide composites were prepared and labelled as Al-2, Al-3 & Al-4. Scanning Electron microscopy (SEM) and energy dispersive X-ray (EDX) study revealed the formation of Cu2O for Al-2. FTIR studies revealed presence of Cu2O for non-heat treated Al-2 and CuO for heat treated Al-2. SEM micrograph showed the porous nature of Al-2, whereas, the least porosity was shown by Al-3. The resultant foils were electrochemically characterized using Cyclic Voltammetry, Electrochemical impedance spectroscopy and Galvanostatic Charge Discharge techniques. On deposition of carbon on cuprous oxide surface, capacitance value of the composite decreased. Among them capacitance of Al-2 was found to be 475mFg−1 from the galvanostatic charge discharge studies. The capacitance was found to be 419.12mFg−1 and 296.87mFg−1 for Al-3 and Al-4 respectively.

Cerotic acid assisted sol-gel synthesis and electrochemical performance of double doped spinels (LiCrxMgyMn2-x-yO4) as cathode materials for lithium rechargeable batteries

LiMn2O4 and LiCrxMgyMn2-x-yO4 (x=0.50; y=0.05–0.50) powders are synthesized via sol-gel method for the first time using Cerotic acid as chelating agent. The synthesized spinel samples have been subjected to physical and electrochemical characterization viz., thermo gravimetric analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical characterization viz., electrochemical galvanostatic cycling studies, electrochemical impedance spectroscopy (EIS) and differential capacity curves (dQ/dE). XRD finger print patterns of LiMn2O4 and LiCrxMgyMn2-x-yO4 ratifies the high degree of crystallinity with single phase compound. FESEM image of undoped pristine spinel clearly depicts uniform spherical surface morphology with an average particle size of 0.5μm while LiCr0.5Mg0.05Mn1.45O4 samples depicting the cabbage morphology somewhat large good agglomerated particles of 200nm.TEM images of LiMn2O4 and LiCr0.5Mg0.05Mn1.45O4 particles depict that the synthesized particles are nano-sized (100nm) with spherical morphology and cloudy agglomerated particle size of 200nm. Charge-discharge studies of LiMn2O4 samples calcined at 850°C deliver the high discharge capacity of 130mAhg−1 corresponds to 94% columbic efficiency during the first cycle, while LiCr0.5Mg0.05Mn1.45O4 delivering 123mAhg−1 corresponds to 81% columbic efficiency in the first cycle. Inter alia, all four dopant compositions investigated, LiCr0.5Mg0.05Mn1.45O4 delivers the maximum discharge capacity of 119, 114mAhg−1 in 5th and 10th cycle with a low capacity fade of 0.1, 0.1 mAh g−1cycle−1 and columbic efficiency of 99, 99%.

Nanocrystalline Manganese Iron Oxide as a Charge Storage Electrode

AbstractPhase pure nanocrystalline manganese iron oxide [(Mn0.37Fe0.63)2O3] was synthesized by combustion technique based on propellant chemistry principle employing citric acid as fuel. The synthesized powder was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), BET, BJH analysis and electrochemical studies for possible application as a charge storage electrode. The average crystallite size was found to be 18.6 nm from XRD analysis. BET analysis yielded the surface area and specific pore volume of the powder to be 22.96 m2 g−1 and 0.0098 cm3 g−1 respectively. The specific capacitance from cyclic voltammetric studies at scan rate 5 mV s−1 was found to be about 30 F g−1 cm−2 while from charge discharge studies was found to be 27±1 F g−1 cm−2. In addition, the material showed appreciable stability during charge‐discharge cycling.

A comprehensive investigation on electrophoretic self-assembled nano-Co3O4 films in aqueous solution as electrode materials for supercapacitors

In this study, the nano-Co3O4 films (NCOFs) have been prepared by a one-step cathodic electrophoretic deposition (C-EPD) in aqueous solutions with micro-additive polyethylenimine at ambient temperature and pressure for oxide film-based supercapacitors. The phase composition and morphology of the NCOFs were studied by X-ray diffraction (XRD) and focused ion beam scanning electron microscope (FIB-SEM), respectively. In addition, the deposition kinetics of nano-Co3O4 particles using C-EPD process were investigated in detail. The electrochemical capacitance behaviors of the NCOFs electrode were analyzed by cyclic voltammetry, galvanostatic charge–discharge studies, and electrochemical impedance spectroscopy in 2 M KOH solution. The electrochemical experiments revealed that the highest capacitance of 233.6 F g−1 at 0.5 A g−1, 93.5 % of which still be maintained after 2000 charge–discharge cycles. These findings suggested the potential application of the NCOFs prepared by C-EPD in the electrochemical supercapacitors.

Poly(Acrylic acid)⁻Based Hybrid Inorganic⁻Organic Electrolytes Membrane for Electrical Double Layer Capacitors Application.

Nanocomposite polymer electrolyte membranes (NCPEMs) based on poly(acrylic acid)(PAA) and titania (TiO2) are prepared by a solution casting technique. The ionic conductivity of NCPEMs increases with the weight ratio of TiO2.The highest ionic conductivity of (8.36 ± 0.01) × 10−4 S·cm−1 is obtained with addition of 6 wt % of TiO2 at ambient temperature. The complexation between PAA, LiTFSI and TiO2 is discussed in Attenuated total reflectance-Fourier Transform Infrared (ATR-FTIR) studies. Electrical double layer capacitors (EDLCs) are fabricated using the filler-free polymer electrolyte or the most conducting NCPEM and carbon-based electrodes. The electrochemical performances of fabricated EDLCs are studied through cyclic voltammetry (CV) and galvanostatic charge-discharge studies. EDLC comprising NCPEM shows the specific capacitance of 28.56 F·g−1 (or equivalent to 29.54 mF·cm−2) with excellent electrochemical stability.

Effect of Metal Ions Doping on the Structural and Electrochemical Properties of Olivine LiFePO4

Li ion rechargeable batteries have better performance over the other competitive rechargeable batteries due to their higher operative voltage (around 3-4 v range), high-energy storage capacity, low self-discharge, and high cycleability. For the application in high power devices (various consumer electronic products such as laptop, camcorder, etc.) the discharge capacity of Li ion batteries at higher current rate required is to be improved. As diffusion of lithium ions inside the active material particles is the rate-limiting step of intercalation process, faster Li+ diffusion in the electrode materials could improve the rate capabilities of Li ion batteries. Olive LiFePO4 is a very promising cathode material used in lithium ion batteries, due to its environmental friendliness, high theoretical capacity (170 mAhg-1), low cost of precursors, high reversibility of Li+ insertion/extraction, good thermal stability, and lack of toxicity. In spite of these attractive features, LiFePO4 requires further modifications to overcome limitations such as poor electronic conductivity and slow lithium ion diffusion. In this work we have synthesized olivine LiFe1-xMxPO4 (M = Nb, Yb, Sb, Mg)(LFMPO) powders by chemical synthesis and co-precipitation method. The synthesized powders were used to prepare cathodes for Li ion coin cells. The structural and electrochemical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared, Raman spectroscopy, cyclic voltammetry and charge-discharge studies, respectively. The phase pure and crystalline quality of the materials was studied from XRD peaks and their line widths respectively. 7Li magic angle spinning nuclear magnetic resonance were used to compare the cation arrangement in the undoped and doped powders. The cyclic voltammetry of both the cathodes revealed the reversible nature of Li-ion intercalation in the cell. The dopant induced structural and stoichiometric modifications were correlated with the voltage cycling and charge discharge characteristics of these cathode materials.

Growth, microstructure and supercapacitive performance of copper oxide thin films prepared by RF magnetron sputtering

The supercapacitive performance of copper oxide thin film electrodes mainly relies on micro structure, phase, surface area and conductivity which in turn depend on the deposition technique and process parameters during growth. In the present study, thin films of copper oxide were prepared by RF magnetron sputtering on stainless steel substrates keeping O2-to-Ar ratio at 1:11 and RF power at 250 W and varying the substrate temperature. The microstructure and the induced phase changes in copper oxide films are observed to be strongly influenced by the substrate temperature since the relaxation time, surface diffusion and surface structural changes are thermally activated. The XRD and Raman studies reveal that the films deposited at low substrate temperature ( 200 °C exhibited Cu2O phase. The films prepared at 350 °C exhibited reflections correspond to cubic Cu2O with predominant (111) orientation. The estimated maximum grain size from AFM studies was 72 nm with surface roughness of 51 nm. These films exhibited a highest areal capacitance of 30 mF cm−2 at scan rate of 5 mV s−1. The galvanostatic charge–discharge studies demonstrated high specific capacitance of 908 F g−1 at 0.5 mA cm−2 current density with 80 % of its initial capacity retention even after 1000 cycles.

Single-Step Synthesis of Halogenated Graphene through Electrochemical Exfoliation and Its Utilization as Electrodes for Zinc Bromine Redox Flow Battery

We have demonstrated a single step synthesis of halogen functionalized graphenes (HGs) through electrochemical exfoliation of graphite in aqueous potassium halide solutions. Few layers of as-synthesized HGs are characterized using powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Electron paramagnetic spectroscopy (EPR), Brunauer-Emmett-Teller (BET) surface area analysis, Field emission scanning electron microscopy (FESEM), and Transmission electron microscopy (TEM). The degree of halogenation is found to vary between 2.32 and 0.26 atomic % in fluorinated graphene (FG) and iodinated graphene (IG) respectively, which could be attributed to the difference in reactivity of the halogen species generated during the exfoliation process. A suitable mechanism is proposed in accordance with the exfoliation phenomena and functionalization of halogens on the graphene sheets based on the experimental observation. As synthesized HGs are utilized as electrode materials for zinc bromine flow batteries (ZBB) and the electrocatalytic effect of HGs electrodes for the 2Br−/Br2 redox couple has been investigated in detail. Cyclic voltammetry (CV), and charge-discharge studies were carried out to study the electrochemical performance of the HGs. Among all HGs, FG has shown the superior electrocatalytic behavior for 2Br−/Br2 redox reaction. The anodic (11.2 mA cm−2) and cathodic (10.7 mA cm−2) peak current densities are higher for FG than that of other halogenated graphenes. ZBB flow cell fabricated with FG as bromine electrode exhibits enhanced electrochemical performance in terms of efficiency (81% of voltaic efficiency and 72% energy efficiency) and durability up to 350 cycles.