Solid-state Electric Double Layer Capacitors Research Articles

Solid-state electric double layer capacitors fabricated with plastic crystal based flexible gel polymer electrolytes: Effective role of electrolyte anions

Flexible gel polymer electrolyte (GPE) thick films incorporated with solutions of lithium trifluoromethanesulfonate (Li-triflate or LiTf) and lithium bis trifluoromethane-sulfonimide (LiTFSI) in a plastic crystal succinonitrile (SN), entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP) have been prepared and characterized. The films have been used as electrolytes in the electrical double layer capacitors (EDLCs). Coconut-shell derived activated carbon with high specific surface area (∼2100 m2 g−1) and mixed (micro- and meso-) porosity has been used as EDLC electrodes. The structural, thermal, and electrochemical characterization of the GPEs have been performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impedance measurements and cyclic voltammetry. The high ionic conductivity (∼10−3 S cm−1 at 25 °C), good electrochemical stability window (>4.0 V) and flexible nature of the free-standing films of GPEs show their competence in the fabrication of EDLCs. The EDLCs have been tested using electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. The EDLCs using LiTf based electrolyte have been found to give higher values of specific capacitance, specific energy, power density (240–280 F g−1, ∼39 Wh kg−1 and ∼19 kW kg−1, respectively) than the EDLC cell with LiTFSI based gel electrolyte. EDLCs have been found to show stable performance for ∼104 charge–discharge cycles. The comparative studies indicate the effective role of electrolyte anions on the capacitive performance of the solid-state EDLCs.

Solid-State Planar Edlc Design Enabled By Hydroxide-Conducting Polymer

Electrolytic capacitors are the current solution for 120 Hz power filtering. However such devices are bulky, which limits power electronics miniaturization. Electric double layer capacitors (EDLCs), often referred to by the product name Supercapacitor, have much higher volumetric charge storage and potentially should allow for a size reduction in the power electronics. For an EDLC to be capable of efficient AC line filtering, its impedance phase angle at 120 Hz must reach or be close to -90 degree. The very first EDLC that met this requirement was fabricated using vertically-oriented graphene with a liquid KOH electrolyte [1]. Both series resistance and distributed charge storage were minimized to reach this level of performance. Further development has led to a planar interdigitated cell design, which offers volumetric advantages and a simple approach for series-connecting cells [2]. With this design, polymer electrolytes are preferred since they can cover each planar cell without flowing to an adjacent cell. In the past, we have demonstrated a tetraethylammonium hydroxide (TEAOH)-based polymer electrolyte system that outperformed the KOH-based polymer electrolytes [3]. In this study, we leveraged the TEAOH polymer electrolyte and the vertically-oriented graphene to demonstrate solid-state planar EDLC cells. Impedance behavior of the cells at both room temperature and elevated temperatures was investigated. Two polymer electrolyte systems based on TEAOH were studied: (a) TEAOH-polyvinyl alcohol (TEAOH-XLPVA); and (b) TEAOH- polyacrylamide (TEAOH-PAM). Utilizing these polymer electrolytes, we assembled solid-state EDLC cells using vertically-oriented graphene electrodes. These solid-state devices were first tested at room temperature for aging stability and then at higher temperature for thermal stability. Figure 1 shows three plots of capacitance versus frequency for TEAOH-based electrolyte solid-state EDLCs. The capacitance values were calculated assuming a series-RC circuit model. While both TEAOH-PAM-based and TEAOH-XLPVA-based electrolyte cells showed capacitive behavior, the former exhibited higher initial capacitance than the latter (38 vs. 32 μF at 120 Hz). Although both capacitors showed slightly reduced capacitance after ca.25 days storage without packaging (Fig. 1a), both capacitors demonstrated good shelf life at room temperature. Further evaluations of the thermal stability of these capacitors at elevated temperatures were performed at temperatures up to 110 oC (Fig. 1b and 1c). Capacitance increased with increasing temperature for both solid-state electrolytes. A detailed analysis including comparisons will be presented. Capacitor equivalent series resistance and characteristic response times will be discussed.

Electric double-layer capacitors with corn starch-based biopolymer electrolytes incorporating silica as filler

Solid-state electric double-layer capacitors (EDLCs) based on corn starch biodegradable polymer electrolytes are fabricated. Silica is added into the corn starch polymer electrolytes to improve the ionic conductivity and capacitance of the EDLCs. The ionic conductivity as a function of temperature obeys the Arrhenius equation indicating ionic hopping mechanism in the polymer electrolytes. Linear sweep voltammetry shows that the prepared corn starch-based biopolymer electrolyte is stable in the range from −2.5 to 2.5 V. Electrical capacitance performances of these capacitors are studied by cyclic voltammetry, galvanostatic charge–discharge, and AC impedance spectroscopy. The discharge characteristics have been found to be almost linear, which confirms the capacitive behavior of the EDLC cell. The fabricated EDLC cells perform good cyclability up to 500 cycles with more than 90 % of coulombic efficiency.

Boron cross-linked graphene oxide/polyvinyl alcohol nanocomposite gel electrolyte for flexible solid-state electric double layer capacitor with high performance

A new family of boron cross-linked graphene oxide/polyvinyl alcohol (GO-B-PVA) nanocomposite gels is prepared by freeze-thaw/boron cross-linking method. Then the gel electrolytes saturated with KOH solution are assembled into electric double layer capacitors (EDLCs). Structure, thermal and mechanical properties of GO-B-PVA are explored. The electrochemical properties of EDLCs using GO-B-PVA/KOH are investigated, and compared with those using GO-PVA/KOH gel or KOH solution electrolyte. FTIR shows that boron cross-links are introduced into GO-PVA, while the boronic structure inserted into agglomerated GO sheets is demonstrated by DMA analysis. The synergy effect of the GO and the boron crosslinking benefits for ionic conductivity due to unblocking ion channels, and for improvement of thermal stability and mechanical properties of the electrolytes. Higher specific capacitance and better cycle stability of EDLCs are obtained by using the GO-B-PVA/KOH electrolyte, especially the one at higher GO content. The nanocomposite gel electrolytes with excellent electrochemical properties and solid-like character are candidates for the industrial application in high-performance flexible solid-state EDLCs.

High Performance Solid-State Electric Double Layer Capacitor from Redox Mediated Gel Polymer Electrolyte and Renewable Tamarind Fruit Shell Derived Porous Carbon

The activated carbon was derived from tamarind fruit shell and utilized as electrodes in a solid state electrochemical double layer capacitor (SSEDLC). The fabricated SSEDLC with PVA (polyvinyl alcohol)/H2SO4 gel electrolyte delivered high specific capacitance and energy density of 412 F g(-1) and 9.166 W h kg(-1), respectively, at 1.56 A g(-1). Subsequently, Na2MoO4 (sodium molybdate) added PVA/H2SO4 gel electrolyte was also prepared and applied for SSEDLC, to improve the performance. Surprisingly, 57.2% of specific capacitance (648 F g(-1)) and of energy density (14.4 Wh kg(-1)) was increased while introducing Na2MoO4 as the redox mediator in PVA/H2SO4 gel electrolyte. This improved performance is owed to the redox reaction between Mo(VI)/Mo(V) and Mo(VI)/Mo(IV) redox couples in Na2MoO4/PVA/H2SO4 gel electrolyte. Similarly, the fabricated device shows the excellent capacitance retention of 93% for over 3000 cycles. The present work suggests that the Na2MoO4 added PVA/H2SO4 gel is a potential electrolyte to improve the performance instead of pristine PVA/H2SO4 gel electrolyte. Based on the overall performance, it is strongly believed that the combination of tamarind fruit shell derived activated carbon and Na2MoO4/PVA/H2SO4 gel electrolyte is more attractive in the near future for high performance SSEDLCs.

Chitosan hydrogel-based electrode binder and electrolyte membrane for EDLCs: experimental studies and model validation

Experimental studies and model validation thereof on all solid-state electrical double layer capacitors (EDLCs) comprising of a novel, cost-effective, and eco-friendly electrode binder consisting of chitosan chemical hydrogel (CCH), and a separator consisting of ionically cross-linked chitosan hydrogel membrane electrolyte (ICCSHME) are reported. The EDLCs have been assembled with black pearls carbon as electrode. The ICCSHME has been prepared by ionic cross-linking of chitosan (CS) with sodium sulfate. EDLCs comprising 40 % loading of CCH electrode binder and ICCSHME with 1 M NaOH dopant have been studied by galvanostatic chronopotentiometry. The data have been analyzed using mathematical modeling to study lifetime behavior of the EDLCs.

Electrochemical Characterization of Solid-State Electric Double Layer Capacitors assembled with Sulfonated Poly(Ether Ether Ketone)

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All solid-state electric double-layer capacitors based on alkaline polyvinyl alcohol polymer electrolytes

Solid-state electrochemical double-layer capacitors (ELDCs) based on alkaline polyvinyl alcohol (PVA) solid polymer electrolytes (SPEs) are prepared. Electrochemical capacitance performance of these capacitors is studied by cyclic voltammetry, galvanostatic charge–discharge testing, and ac impedance spectroscopy. For comparison, two types of EDLC cells are constructed and tested. It is found that an EDLC with a PVA polymer electrolyte exhibits much higher capacitance and longer cycle-life than one with the PP/PE separator. The specific capacitance for the EDLC with the PVA-based SPE is in the range of 100–112 F g −1, and depends on the scan rate or the charge–discharge current rates. The results also indicate that the solid-state EDLC shows a relatively stable specific capacitance of 100 F g −1 after 1000 cycles. The findings suggest that the PVA-based SPE is a promising material for use in EDLCs.

Proton-Conductive Composites Composed of Phosphoric Acid-Doped Silica Gel and Organic Polymers with Sulfo Groups.

Preparation of highly proton-conductive and thermoplastic composites was successfully pursued from H3PO4-doped silica gel and organic polymers with sulfo groups. The sulfo groups and polystyrene blocks in the organic polymers were found to improve the proton conductivity and molding characteristics of the resultant composite, respectively. The composite composed of H3PO4-doped silica gel with a molar ratio=0.5 of H3PO4/SiO2 in 80mass% and sulfonated styrene-isoprene-styrene (SIS-SO3H) block copolymer in 20 mass% showed a high electrical conductivity of 10-4S·cm-1 at 25°C in dry N2 atmosphere and good molding characteristics. The temperature dependence of the electrical conductivity of the composite was of the Vogel-Tamman-Fulcher type, indicating that proton transferred through a liquid-like phase present in the composites consisting of silica gel and organic polymer. The elastic modulus of the composite was larger by one to two orders of magnitude than that of the SIS-SO3H elastomer. The thermoplastically deforming temperature of the composite was around 130°C, which was higher by 50°C than that of the SIS elastomer itself. The capacitance of a totally solid state electric double-layer capacitor, which was fabricated using the composite as a solid electrolyte, was comparable to those of the conventional capacitors with liquid electrolytes.

Electric double-layer capacitor using composites composed of phosphoric acid-doped silica gel and styrene–ethylene–butylene–styrene elastomer as a solid electrolyte

Solid state electric double-layer capacitors have been fabricated using a composite composed of H 3 PO 4 -doped silica gel and styrene–ethylene–butylene–styrene elastomer as the electrolyte. A composite hybridized with activated carbon powders (ACP) was the polarizable electrode. The cyclic voltammogram of the electric double-layer capacitor fabricated demonstrated that electric charge was stored in the electric double-layer at the interface between the polarizable electrode and the electrolyte. Resistance of the capacitor obtained from impedance plots in ambient air was smaller by three orders of magnitude than that of the capacitor in a dry Ar atmosphere. The drastic decrease in the resistance should be ascribed to the increase in the proton conductivity of the composite due to the water adsorption in H 3 PO 4 -doped silica gel in an ambient atmosphere. The value of capacitance of the capacitor in an ambient atmosphere was 10 F/(gram of total ACP), which was 10 times larger than that of the capacitor in a dry Ar atmosphere. The large capacitance of the capacitor in an ambient atmosphere is attributable to the formation of electric double-layer with large electric charge at the interface between the composite and ACP in the capacitor due to the water adsorption.

Electric double-layer capacitors using HClO 4-doped silica gels as a solid electrolyte

Electric double-layer capacitors were fabricated using polyvinyl alcohol-containing silica gels doped with HClO 4 as an electrolyte and activated carbon powders, ACP, hybridized with the silica gels as a polarizable electrode. One of the capacitors fabricated had capacitance of 44 F/(gram of total ACP in the capacitor) at room temperature. The large capacitance of the totally solid state electric double-layer capacitors fabricated is ascribed to the high proton conductivity of the gels and the homogeneous hybridization of ACP with the gels by the sol-gel process.

Proton Conductive Silica Gels Doped with Several Acids and Their Application to Electric Double-Layer Capacitor

Abstract Polyvinyl alcohol-containing silica gels doped with HClO4, H2SO4, or H3PO4 prepared by the sol-gel method exhibited high proton conductivities of 10−5-10−2S cm−1 at room temperature. Totally solid state electric double-layer capacitors fabricated using the gels as an electrolyte and activated carbon powder, ACP, as a polarizable electrode showed large capacitances of 31-44F/(gram of total ACP), which were comparable to those of the capacitors with liquid electrolytes.

New solid-state electric double-layer capacitor using poly(vinyl alcohol)-based polymer solid electrolyte

Poly vinyl alcohol (PVA) dissolves large amounts of lithium salts (up to about 1.5 g/g of PVA) such as LiCF 3SO 3, LiClO 4 and LiBF 4 in its polymer matrix. The composites obtained show good ionic conductivity. When the PVA—lithium salt composites are used as the solid electrolyte in solid-state electric double-layer capacitors with porous and electrically conducting clay carbon composites as polarizable electrodes, the solid-state electric double-layer capacitors show good charge/discharge behavior with large capacitance of 2.5–3.5 F/(cm 3 of the capacitor).