Loss Of Specific Capacitance Research Articles

Improved Electrochemical Performance By Templating Carbon-Sulfur Composite Electrodes for Lithium-Sulfur Batteries

Replacing fossil energy sources by renewable and clean energies is of large importance for decades to come. The mainly electric and intermittent renewables energies require proper electricity storage systems that must be: clean, economical, efficient, long life, safe and have high specific capacities (mass and volume). For Argentina, with its significant reserves of lithium in the north west of the country, developments on lithium-ion battery technology are of paramount importance. Current research in Argentina is carried out to improve future lithium battery prospects. Focus is on development and characterization of new active materials for Li-ion battery electrodes, and on systems beyond Li-ion. Li-S batteries are promising candidates to replace current Li-ion technology. In the case of C-S composite cathodes, there are several factors regarding the composition and structure that affect the performance of the battery. Nonetheless, little is known on how the architecture of the composite electrode influences the electrochemical performance of the battery. The present work consists of a systematic investigation of the influence of two very important factors regarding composite electrode fabrication and cell assembly. The factors that are considered are the electrode architecture, modified by templating, and the electrolyte to sulfur ratio. A full factorial two-by-three experimental design is employed, considering five response variables: the initial and final specific capacity of the sulfur cathode, the specific capacity loss per cycle, as well as the initial and final cell energy density. All battery cells are tested for 100 cycles galvanostatically with a C/10 current. Statistically significant factors and their interactions are identified.

High Capacity Retention Anode Material for Lithium Ion Battery

Capacity fading of lithium ion batteries (LIBs) is a huge hurdle for their commercial utilization that may be reduced by the insertion of high quality anode material. Herein, we introduce high-graphitized graphene foam (GF) as anode material, which can be helpful for minimizing the loss of specific capacity during electrochemical reactions. GF shows excellent results when employed as anode in LIBs with high capacity values of 497mAhg−1 along with very low capacity fading (∼0.00578% at a current density of 200mAg−1).

Electrochemical performance of supercapacitors based on carbon nanofoam composite and microporous poly(3, 4-ethylenedioxythiophene) thin film asymmetric electrodes

Electrochemical performance of supercapacitors configured using carbon nanofoam enfolded by conformal thin poly(3,4-ethylenedioxythiophene) (PEDOT) film in nanofibrous structure and electrodeposited microporous PEDOT film/graphite as two asymmetric electrodes is described. Cyclic voltammetry data at 20 mV s−1 scan rate show specific capacitance of carbon nanofoam-PEDOT composite electrode operating in the −0.8 to +0.2 V, and microporous PEDOT in the 0 to +0.8 V voltage range are 72 and 159 F g−1, respectively. Paired in an asymmetric supercapacitor, in the balanced charge state, highly symmetrical cyclic voltammetry plots at high scan rates of 100 mV s−1 in −0.8 to +1.2 V voltage range testify highly capacitive behavior with high degree of charge reversibility. This is attributed to unimpeded pore-filling and alignment of ionic charges over vast interiors of carbon nanofoam and a highly pervasive access to electrolyte ions within interconnected void network of microporous PEDOT. Linear charge-discharge characteristic of the supercapacitor at 1.0 to 3.5 A g−1 current density show high rate capability and yield energy density of 13.6 Wh kg−1 at the power density of 19.0 kW kg−1. The long term charge-discharge tests at 1 A g−1 show minimal ∼14% loss of specific capacitance of asymmetric supercapacitor for 10,000 cycles.

The truth about the 1st cycle Coulombic efficiency of LiNi1/3Co1/3Mn1/3O2 (NCM) cathodes.

The 1st cycle Coulombic efficiency (CE) of LiNi1/3Co1/3Mn1/3O2 (NCM) at 4.6 V vs. Li/Li(+) has been extensively investigated in NCM/Li half cells. It could be proven that the major part of the observed overall specific capacity loss (in total 36.3 mA h g(-1)) is reversible and induced by kinetic limitations, namely an impeded lithiation reaction during discharge. A measure facilitating the lithiation reaction, i.e. a constant potential (CP) step at the discharge cut-off potential, results in an increase in specific discharge capacity of 22.1 mA h g(-1). This capacity increase during the CP step could be proven as a relithiation process by Li(+) content determination in NCM via an ICP-OES measurement. In addition, a specific capacity loss of approx. 4.2 mA h g(-1) could be determined as an intrinsic reaction to the NCM cathode material at room temperature (RT). In total, less than 10.0 mA h g(-1) (=28% of the overall capacity loss) can be attributed to irreversible reactions, mainly to irreversible structural changes of NCM. Thus, the impact of parasitic reactions, such as oxidative electrolyte decomposition, on the irreversible capacity is negligible and could also be proven by on-line MS. As a consequence, the determination of the amount of extracted Li(+) ("Li(+) extraction ratio") so far has been incorrect and must be calculated by the charge capacity (=delithiation amount) divided by the theoretical capacity. In a NCM/graphite full cell the relithiation amount during the constant voltage (CV) step is smaller than in the half cell, due to irreversible Li(+) loss at graphite.

Design and synthesis of ternary Co3O4/carbon coated TiO2 hybrid nanocomposites for asymmetric supercapacitors.

Recently, attention has been focused on the synthesis and application of nanocomposites for supercapacitors, which can have superior electrochemical performance than single structured materials. Here, we report a carbon-coated TiO2/Co3O4 ternary hybrid nanocomposite (TiO2@C/Co) electrode for supercapacitors. A carbon layer was directly introduced onto the TiO2 surface via thermal vapor deposition. The carbon layer provides anchoring sites for the deposition of Co3O4, which was introduced onto the carbon-coated TiO2 surface by hydrazine and the thermal oxidation method. The TiO2@C/Co electrode exhibits much higher charge storage capacity relative to pristine TiO2, carbon-coated TiO2, and pristine Co3O4, showing a specific capacitance of 392.4 F g(-1) at a scan rate of 5 mV s(-1) with 76.2% rate performance from 5 to 500 mV s(-1) in 1 M KOH aqueous solution electrolyte. This outstanding electrochemical performance can be attributed to the high conductivity and high pseudo-capacitive contributions of the nanoscale particles. To evaluate the capacitive performance of a supercapacitor device employing the TiO2@C/Co electrode, we have successfully assembled TiO2@C/Co//activated carbon (AC) asymmetric supercapacitors. The optimized TiO2@C/Co//AC supercapacitor could be cycled reversibly in the voltage range from 0 to 1.5 V, and it exhibits a specific capacitance of 59.35 F g(-1) at a scan rate of 5 mV s(-1) with a specific capacitance loss of 15.4% after 5000 charge-discharge cycles. These encouraging results show great potential in terms of developing high-capacitive energy storage devices for practical applications.

Synthesis of Porous Ni–Co–Mn Oxide Nanoneedles and the Temperature Dependence of Their Pseudocapacitive Behavior

Porous Ni-Co-Mn oxide nanoneedles have been synthesized on Ni foam by a facile one-step hydrothermal method for use as supercapacitor electrodes. Structural and compositional characterizations indicate that Ni, Co and Mn elements are homogeneously distributed within the multi-component metal oxides. Such multi-component metal oxides with a homogenous structure exhibit high specific capacitance of 2023 F g-1 at 1 mA cm-2, high coulombic efficiencies (greater than 99%), and good long-term cycle life (approximately 7% loss in specific capacitance over 3000 charge/discharge cycles) at room temperature. Moreover, the influence of temperature on the electrochemical performance of the electrodes has been characterized at temperatures ranging from 4 to 80°C in aqueous electrolytes. The thermal behavior of the electrodes reveals that elevated operating temperature promotes higher capacitance and lower internal resistance by decreasing the ionic conductivity of the electrolyte and increasing redox reaction rates at the interface of the electrodes and electrolytes. The capacitance of the electrodes increases by 84% at a nominal temerature of 80°C and decreases by 18% at 4°C, compared to that at room temperature (RT). The overall set of results demonstrates that the new Ni-Co-Mn oxide nanoneedle electrodes are promising for high-performance pseudocapacitive electrodes with a wide usable temperature range.

Cobalt–carbon derived from zeolitic imidazolate framework on Ni foam as high-performance supercapacitor electrode material

Abstract ZIF-67 (Co(MeIM)2, MeIM = 2-methylimidazole) was selected as a precursor to synthesize the metallic cobalt/carbon composites on Ni foam directly and intimately. The results show that ZIF-67 forms a uniform membrane and densely covers the Ni foam substrate. Besides, the cobalt/carbon composites obtained are composed of cobalt nanoparticles with a diameter up to around 2.6 nm, which are anchored on carbon homogeneously. The specific capacitance of the composites material is up to 512 F g−1 at a current density of 1 A g−1 in 1.0 M KOH electrolyte. Furthermore, the specific capacitance loss is ∼46.4% with increase at the current density from 1 to 20 A g−1. More significantly, the specific capacitance retention rate is 87.5% at a current density of 5 A g−1 after 1000 cycles. These results suggest that the electrochemical performance can be greatly enhanced by the well-controlled size and distribution of the cobalt nanoparticles, which is mainly attributed to the unique structure and composition of ZIF-67.

PAN Esaslı Karbon Lif Üretiminde Termal Dönüşüm Prosesinin Ekzerjetik Analizi

The processes of stabilisation and carbonisation in carbon fibre manufacture provides a large energy saving potential if an adequate furnace technology and process control is used. In this paper a general exergetic balance equation for the processes of stabilisation and carbonisation with the objective to determine the exergetic costs of producing carbon fibres is placed. After a short theoretical explanation of the carbon fibre manufacturing processes, this paper will resort to the general laws of thermodynamics and later determine the exergy of heat and mass flows in the processes. Experiments are carried out in a DSC and TGA combined with a mass spectrometry to determine the composition of the evolved gases during the stabilisation process. Furthermore DSC and TGA measurements are used to determine specific heat capacity and mass loss of the polyacrylonitrile precursor material. Included in the exergetic balance equation the measured material values leads to an exergy efficiency result of the carbon fibre conversion reaction.

LiFePO<sub>4 </sub>- Activated Carbon Composite Electrode as Symmetrical Electrochemical Capacitor in Mild Aqueous Electrolyte

In this study, a symmetric electrochemical capacitor has been fabricated by adopting the lithiated compound (LiFePO4)-activated carbon (AC) composite as the core electrode materials. The electrochemical performances of the prepared supercapacitor were studied using cyclic voltammetry (CV) in 1.0 M Na2SO3 solution. Experimental results reveal that the maximum specific capacitance of 112.41 F/g is obtained in 40 wt % LiFePO4 loading on AC electrode in comparison to that of pure AC electrode (76.24 F/g) in 1 M Na2SO3. The enhanced capacitive performance of the 40 wt % LiFeO4 –AC composite electrode is believed attributed to the contribution of synergistic effect of electric double layer capacitance (EDLC) on the surface of AC as well as pseudocapacitance via intercalation/extraction of Na+, SO32-and Li+ ions in LiFePO4 lattices. The composite electrodes can sustain a stable capacitive performance at least 1000 cycles with only ~5 % specific capacitance loss after 1000 cycles. Based on the findings above, 40 wt % LiFeO4 –AC composite electrodes which utilise low cost materials and environmental friendly electrolyte is worth being investigated in more details.

Study of properties of cathode materials based on lithium-iron phosphate

The influence of the structure of a cathode based on lithium-iron phosphate on its electrochemical characteristics is studied. It is found experimentally that there is an optimal ratio of its components: 82% of LiFePO4: 8% of carbon nanotubes (UNT): 10% of solid polymeric electrolytes (SPE). Solid-phase cathodes possess specific capacity of approximately 150 mA h/g and are reversibly cycling at the current density of 0.01–0.15 mA/cm2. Loss of specific capacity in 100 charge-discharge cycles is 0.06% per cycle, which is much better than that of the existing analogs.

An Asymmetric Ultracapacitors Utilizing α-Co(OH)2/Co3O4 Flakes Assisted by Electrochemically Alternating Voltage

α-Co(OH)2/Co3O4 flakes were obtained through alternating voltage induced electrochemical methodology at room temperature. The as-prepared α-Co(OH)2/Co3O4 flakes displayed a high specific capacitance of 583 F g−1 at a current density of 1 A g−1. An asymmetric supercapacitor is further fabricated with the α-Co(OH)2/Co3O4 nanocomposite as the anode and activated carbon as the cathode in 2M aqueous KOH solution as electrolyte. This asymmetric capacitor exhibited a maximum energy density of 22.4 Wh kg−1 at power density of 290Wkg−1. Moreover, the asymmetric supercapacitor showed an excellent cycling stability without obvious specific capacitance loss after 2000 cycles at a current density of 1 A g−1.

Far-infrared reduced graphene oxide as high performance electrodes for supercapacitors

We report a novel far-infrared (FIR) thermal reduction process to effectively reduce graphene oxide films for supercapacitor electrode applications. The binder-free graphene oxide films used in this study were produced by electro-spray deposition of a graphene oxide colloidal solution onto stainless steel current collectors. The reduction of graphene oxide was performed using a commercial FIR convection oven that is ubiquitous in homes for cooking and heating food. The reduction process incorporated a simple, one-step FIR irradiation carried out in ambient air. Further, the FIR irradiation process was completed in ∼3min, wherein neither special atmosphere nor high temperature was employed, resulting in an economic, efficient and simplified processing technique. The as-produced FIR graphene electrode gave a specific capacitance of ∼320F/g at a current density of ∼0.2A/g with less than 94% loss in specific capacitance over 10,000 charge/discharge cycles. This is one of the best specific capacitances reported for all-carbon electrodes without any additives. Even at ultrafast charge/discharge rates (current densities as high as ∼100A/g), the FIR graphene electrode still delivered specific capacitances in excess of 90F/g. The measured energy and power densities of the FIR supercapacitors were found to be ∼3–6 times higher than commercial (activated carbon) supercapacitor devices. This excellent electrochemical performance of the FIR graphene coupled with its ease of production (in air at low temperatures) using a commercial home-use FIR convection oven indicates the significant potential of this concept for large-scale commercial electrochemical supercapacitor applications.

Effect of tantalum capacitor powder preparation conditions on the dielectric loss tangent of anodes

We have studied the effect of the preparation and agglomeration conditions of tantalum powders produced by sodium reduction on the frequency dependences of the specific capacity and dielectric loss tangent for anodes fabricated from the powders.

Preparation and electrochemical capacitive performance of polyaniline nanofiber-graphene oxide hybrids by oil–water interfacial polymerization

Polyaniline nanofiber-graphene oxide (PANIF-GO) hybrids were fabricated by oil–water interfacial polymerization. The structures of PANIF-GO hybrids, pure PANIF and GO were examined by high resolution transmission electron microscopy. It was found that PANIFs were homogeneously inserted between the GO layers or absorbed on the surface of the GO. Fourier transform infrared spectroscopy and X-ray diffraction showed that PANIFs effectively increased the interlayer distance of GO from 0.83nm to 1.38nm. Electrochemical properties for the hybrid electrode were tested by cyclic voltammetry and electrochemical impedance spectroscopy using a three-electrode system. The results indicated that a high specific capacitance of 564.7Fg−1 for the hybrids was measured at the current density of 0.5Ag−1 in a 1M H2SO4 aqueous solution compared to 352.8Fg−1 for pure PANIF and 30.1Fg−1 for GO. Moreover, the PANIF-GO hybrids showed a very long cycle life with only 9.4% specific capacitance loss after 2000 cycles. The as-prepared hybrids are remarkable electrode materials for the supercapacitors.

Functionalization of graphene with nitrogen using ethylenediaminetetraacetic acid and their electrochemical energy storage properties

Recently there has been a considerable focus on the synthesis of nitrogen functionalized graphene for energy storage and conversion. Herein, we report a simple, economical and facile process for the synthesis of nitrogen containing graphene composite which can be scaled up for mass production by using a nitrogen containing organic compound, ethylenediaminetetraacetic acid (EDTA) and graphene oxide as precursors. From the XRD studies, the increase in the interlayer distance between the graphene sheets confirms the functionalization of graphene sheets and the FT-IR spectroscopic analysis revealed the presence of N-containing functional groups in N-doped graphene sheets. XPS analysis confirms the chemical nature of N-containing functional groups, and TG analysis showed the amount of EDTA loaded on the graphene sheets. This composite exhibits a large specific capacitance of 290 F g−1 at 0.1 A g−1 with a capacitance retention of 67% and 58% at high current densities of 10 and 20 A g−1, respectively, thereby showing superior rate capability. In addition, it showed long-term electrochemical stability through 6000 charge–discharge cycles even at a high current density of 5 A g−1 with a specific capacitance loss of 2%.

Development of high power and energy density microsphere silicon carbide-MnO2 nanoneedles and thermally oxidized activated carbon asymmetric electrochemical supercapacitors.

In order to achieve high energy and power densities, a high-voltage asymmetric electrochemical supercapacitor has been developed, with activated carbon (AC) as the negative electrode and a silicon carbide-MnO2 nanoneedle (SiC-N-MnO2) composite as the positive electrode. A neutral aqueous Na2SO4 solution was used as the electrolyte. SiC-N-MnO2 was prepared by packing growing MnO2 nanoneedle crystal species in only one direction on the silicon carbide surface. AC was oxidized by thermal treatment in order to introduce oxygen-containing functional groups. Owing to the high capacitance and excellent rate performance of SiC-N-MnO2 and AC, as well as the synergistic effects of the two electrodes, a constructed asymmetric supercapacitor exhibited superior electrochemical performance. The optimized asymmetric supercapacitor could be cycled reversibly in the voltage range from 0 to 1.9 V, and it exhibited a specific capacitance of 59.9 F g(-1) at a scan rate of 2 mV s(-1) and excellent energy density and power density (30.06 W h kg(-1) and 113.92 W kg(-1), respectively) with a specific capacitance loss of less than 3.1% after 1000 charge-discharge cycles, indicating excellent electrochemical stability. These encouraging results show great potential in terms of developing energy storage devices with high energy and power densities for practical applications.

Nitrogen- and oxygen-containing activated carbon nanotubes with improved capacitive properties

Nitrogen- and oxygen-containing activated carbon nanotubes have been successfully synthesized via a high temperature carbonization of polypyrrole (PPy) nanotubes followed by chemical activation. The first carbonization step ensures the formation of amorphous carbon nanotubes, which are more stable than PPy to preserve the nanotube morphology during the subsequent chemical activation process. The obtained activated carbon nanotubes with high nitrogen (19.8 wt%) and oxygen contents (11.1 wt%) show enlarged specific areas of 705.9 m2 g−1 compared to that of the pristine carbon nanotubes (212.4 m2 g−1). As expected, the activated carbon nanotubes exhibit enhanced capacitance properties, such as an enlarged specific capacity (384.9 F g−1 at 0.5 A g−1), excellent rate capability (201 F g−1 at 50 A g−1), and more stable cyclic stability (only 2.4% of specific capacitance loss after 500 cycles) due to its abundant micropores, high specific areas and abundant interfacial functional groups. This method is facile, low cost and enables easy production of large quantities, and can be expected to open up new opportunities in designing high-performance carbon electrode materials for supercapacitors.

Enhanced Lithium Ion Battery Cycling of Silicon Nanowire Anodes by Template Growth to Eliminate Silicon Underlayer Islands

It is well-known that one-dimensional nanostructures reduce pulverization of silicon (Si)-based anode materials during Li ion cycling because they allow lateral relaxation. However, even with improved designs, Si nanowire-based structures still exhibit limited cycling stability for extended numbers of cycles, with the specific capacity retention with cycling not showing significant improvements over commercial carbon-based anode materials. We have found that one important reason for the lack of long cycling stability can be the presence of milli- and microscale Si islands which typically form under nanowire arrays during their growth. Stress buildup in these Si island underlayers with cycling results in cracking, and the loss of specific capacity for Si nanowire anodes, due to progressive loss of contact with current collectors. We show that the formation of these parasitic Si islands for Si nanowires grown directly on metal current collectors can be avoided by growth through anodized aluminum oxide templates containing a high density of sub-100 nm nanopores. Using this template approach we demonstrate significantly enhanced cycling stability for Si nanowire-based lithium-ion battery anodes, with retentions of more than ~1000 mA·h/g discharge capacity over 1100 cycles.

Structural and electrochemical performance of Al-substituted β-Ni(OH)2 nanosheets electrodes for nickel metal hydride battery

Al-substituted β-Ni(OH)2 nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy, scanning electron microscopy and transmission electron microscopy. The SEM and TEM images show changes in the microstructure of β-Ni(OH)2 by the addition of Al. The XRD results show that the α-phase Ni(OH)2 appeared in Al-substituted Ni(OH)2 electrodes. The effects of Al content on the electrochemical behaviors are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results demonstrate that the 7mol% of Al in Ni(OH)2 has better electrochemical performance, such as better reaction reversibility, higher proton diffusion coefficient, lower electrochemical impedance, higher specific capacity, and better cyclic stability. The as-prepared 7%-Al-Ni(OH)2 electrode exhibits a specific discharge capacity of 324.5mAhg−1 at 0.2C, 220.6mAhg−1 at 10C, and 198.6mAhg−1 at 30C. The specific capacity loss is less than 8% after 200 charge/discharge cycles at 0.2C and with columbic efficiency higher than 90%. This work suggests that the as-prepared 7%-Al-Ni(OH)2 electrode has a promising future as higher charging/discharging rate materials for nickel metal hydride power battery.

Graphene homogeneously anchored with Ni(OH)2 nanoparticles as advanced supercapacitor electrodes

A green and facile approach was demonstrated to prepare graphene nanosheet/Ni(OH)2 (GNS/Ni(OH)2) composites for supercapacitor materials. GNSs as a support material can offer moderate active sites for the nucleation of Ni(OH)2, as well as an excellent electron transfer path. Then, ultrafine Ni(OH)2 nanoparticles were homogeneously anchored onto the surface of GNSs as spacers to ensure the high electrochemical utilization of the graphene layers and supply the open nano-channels for shortening the ion diffusion pathway. The results show that the GNS/Ni(OH)2 composites exhibit a superior specific capacitance of 1985.1 F g−1 and excellent cycle life with a loss of specific capacitance of only 6.5% after 500 cycles. The improved high electrochemical performance is attributed to the increased electrode conductivity in the presence of the graphene network and the increased effective interfacial area caused by the well-dispersed Ni(OH)2 on the GNSs.