Solid-state Electric Double Layer Capacitors Research Articles

A supramolecular gel polymer electrolyte based on poly(vinyl alcohol) and tannic acid for flexible electrical double layer capacitors

Gel polymer electrolytes (GPEs) for flexible electrical double-layer capacitors (EDLCs) have gained significant attention due to their flexibility and security. However, it remains a great challenge to in situ prepare poly(vinyl alcohol) (PVA)/tannic acid (TA)-based GPEs, which is limited by the strong hydrogen bonds between PVA and TA. Herein, a novel strategy is proposed to in situ fabricate PVA/TA-based GPEs by using ethylene glycol (EG) and H2O as the binary solvent. The EG molecules disturb and weaken the hydrogen bonds, paving the way for the successful preparation of PVA/TA-based GPEs. The optimized GPE shows excellent mechanical properties, flexibility, and an ionic conductivity of 106.9 mS cm−1. The carbon-based solid-state EDLC containing this GPE delivers a voltage window of 0–2 V, an energy density of 21.3 Wh kg−1 at a power density of 480 W kg−1, and specific capacitance retention of around 90% after 10,000 charge/discharge cycles. Moreover, the corresponding flexible solid-state EDLC demonstrates acceptable bendability and robust serviceability. This work may provide a universal strategy for in situ preparation of PVA/TA-based gels in energy storage and other related fields.

All-solid-state electric double layer supercapacitors using Li1.3Al0.3Ti1.7(PO4)3 reinforced solid polymer electrolyte

In this work, we report the fabrication and characterization of all-solid-state supercapacitors based on a conductive filler dispersed solid polymer electrolyte. Fast ionic Li1.3Al0.3Ti1.7(PO4)3 (LATP) reinforced PEO-PEG-LITFSI composite solid polymer electrolyte (CSPE) membranes are prepared by milling assisted route. The electric double-layer capacitor (EDLC) cells, using a hot-roll lamination technique, are fabricated using a CSPE membrane as electrolyte and activated charcoal (surface area ∼ 817m2g−1) on graphite sheet as electrode. The EDLCs display appreciable areal capacitance of ∼ 12 Fcm−2 and ∼40 Fcm−2 at 40 °C and 80 °C, respectively at ∼0.65 mAcm2 and 2 V. These solid-state EDLCs at 40 °C exhibit stability up to ∼16,000 cycles. Further, the electrode-electrolyte (solid-solid) interface remains quite stable after the charge-discharge cycling. The electrical conductivity of the CSPE membranes correlates well with the EDLC performance. The LATP content in the CSPE membranes play important role in enhancing the capacitance. The present investigation suggests that CSPE membranes with conductivity between ∼10−4–10−5 Scm−1 are useful for low-power EDLC applications. The EDLCs cells with LATP dispersed CSPE exhibit better stability during thermal cycling between 40 °C-80 °C.

Activated carbon from composite of palm bio-waste as electrode material for solid-state electric double layer capacitor

This work explores the synergistic advantage of the lignocellulose chemistry of oil palm fiber, empty fruit bunch, and oil palm shell as a composite in activated carbon preparation using physical and chemical activation methods. Using coin cell CR2032–3 V, supercapacitors were fabricated with the prepared activated carbon composite as electrode active material and H3PO4-based gel electrolyte. At a specific power density of 50 WKg−1, electric double-layer capacitors derived from chemically and physically activated carbon composite shows a specific energy density of 8.6 WhKg−1 and 5.8 WhKg−1, respectively. These results were observed to be better than the results of supercapacitors fabricated using liquid electrolytes. Apart from the better performance, the solid-state electric double layer capacitor is relatively lighter, allows miniaturization, flexibility, and mitigates liquid electrolyte leakage.

A Comparative Study of Sulfate-Based Neutral pH Polymer Electrolytes for Low Temperature Applications

Polymer electrolytes are key enablers for solid-state electrical double layer capacitors (EDLCs) that have thin and flexible form factors. Aqueous-based polymer electrolytes with neutral pH are interesting for their non-corrosiveness, intrinsically safe, and wider voltage window from high overpotential on water decomposition [1-3]. Previously, two neutral pH polymer electrolytes based on polyacrylamide (PAM) host and Li2SO4 [4] or Na2SO4 [5] as ion conductor were developed. These two systems demonstrated good chemical stability (shelf-life >30 days) and wide voltage window (1.9 V with activated carbon). Na2SO4-PAM showed higher ionic conductivity than Li2SO4-PAM under ambient conditions. Nonetheless, the effects of temperature and change in structure (e.g. freezing) to the electrochemical performance are still unclear.In this study, the performances of Li2SO4-PAM and Na2SO4-PAM at different temperatures were compared. The objectives were to (i) understand the ion conduction mechanisms within the polymeric structure, (ii) investigate the working temperature range of these electrolytes, and (iii) correlate the ion-conducting behaviour to their respective thermal properties, especially at the temperature below 0 °C. Metallic cells were constructed to study the electrochemical characteristics of the polymer electrolytes, while differential scanning calorimetry (DSC) was employed to characterize the thermal properties.From the activation energy of conduction above ambient temperatures, ion hopping was considered as the primary mechanism for ion movement in both electrolytes. Interestingly, although Li2SO4-PAM was able to maintain capacitive behaviour <0 ˚C, Na2SO4-PAM underwent severe loss in capacitive behaviour and significant loss in ionic conductivity. By comparing the DSC curves against the respective ionic conductivity at low temperatures (Fig. 1), the amount of crystallized water involved during freezing/melting was deduced as the source of this behaviour. This study elucidated the structure-performance relationship of polymer electrolytes at the low temperature conditions.

The Influential Properties of Polymer Electrolytes on the Performance and Longevity of Solids-State Flexible Supercapacitors

Polymer electrolytes are the key enablers for solid-state energy storage including batteries and supercapacitors. Not only they can provide leakage-free thin and flexible form factors for solid supercapacitors, but also they can reduce and simplify the packaging of the devices to increase the actual energy and power densities. An ideal polymer electrolytes for supercapacitor should have: 1) high ionic conductivity; 2) wide electrochemical stability window and chemical stability without undesirable side reactions; 3) good environmental stability and mechanical properties; and 4) low material and processing cost. While most of the research are focusing on attributes 1) and 2) as well as the enabled solid supercapacitor devices in pristine condition, there are very few studies on the long-term service life and shelf life or the failure mechanisms of the polymer electrolytes. Although many polymer electrolytes have excellent performance at the beginning, they deteriorated rapidly over time. These can be related to the material properties (e.g. the crystallinity of the polymer host), the compatibility of ionic conductors and polymer host, sensitivity of the electrolytes to the environment etc. Fig. 1 compares the conductivities of two pairs of polymer electrolytes over a period of 4 weeks. One pair is a OH- ion conducting polymer electrolytes using the same polymer host poly(vinyl-alcohol) (PVA) but different ionic conductors, KOH or tetraethylammonium hydroxide (TEA-OH). The other set is a neutral pH salt polymer electrolytes that have the same Li2SO4 ionic conductor but different polymer hosts, PVA or polyacrylamide (PAM). PVA-KOH has been the most widely used electrolyte in all solid supercapacitors that need alkaline media. However, despite of its initial good performance, it tends to crystalize and dry out [1]. TEAOH-PVA, on the other hand, has a much longer shelf life. The solid capacitor it enabled was functional for AC-line filtering for over 18 month [2]. The neutral polymer electrolytes using Li2SO4 can reach to 2.0 V in solid symmetric supercapacitor devices [3] , which is very promising to increase energy density. Nonetheless, the same ionic conductor with different polymer hosts led to very different trends in the longevity and device shelf life. These differences in long term stability are the results of the intrinsic properties, degree of hydration within the materials and the conduction and failure mechanisms. In this talk, we will address these issues through the examples to show the influential factors on the performance of the polymer electrolytes at different time and temperature and the impact on the longevity of the solid supercapacitor devices. References Gao, J. Li, and K. Lian, "Alkaline quaternary ammonium hydroxides and their polymer electrolytes for electrochemical capacitors", RSC Advances, 4 (41), 21332-21339, 2014.Gao, J. Li, J. Miller, R. Outlaw, S. Butler, and K. Lian, “Solid-state electric double layer capacitors for ac line-filtering", Energy Storage Materials, 4, 66–70, 2016.Virya and K.Lian, “Li2SO4-Polyacrylamide Polymer Electrolytes for 2.0 V Solid Symmetric Supercapacitors”, Electrochemistry Communications, 81, 52–55， 2017. Figure 1

Preparation of starch-based porous carbon electrode and biopolymer electrolyte for all solid-state electric double layer capacitor

An ever-increasing demand for energy coupled with environmental pollution associated with conventional energy production continues to drive the search for alternative renewable energy storage solutions. In this regard, a high surface area (1841 m2 g−1), hierarchically porous (∼1.18 cm3 g−1) and self-inherited nitrogen (2.1 at.wt%) based activated carbon are obtained from Artocarpus heterophyllus seed derived starch as a result of ZnCl2 chemical activation. A flexible, conductive, thermally stable and bio-degradable biopolymer electrolyte film is prepared from Manihot esculenta starch powder. These eco-friendly hierarchically porous architectured carbon electrode and flexible biopolymer electrolytes are employed as significant components in a coin cell-based all-solid-state supercapacitor. The resulting device delivers a high specific capacitance of 240 Fg−1 at 0.5 mA with 97% coulombic efficiency over 2000 cycles. In addition, the device provided excellent specific energy (17 Wh kg−1) and specific power (3823 W kg−1). Interestingly, the starch derived biopolymer electrolyte film, when buried under soil, shows a favourable natural rate of degradation. Therefore, this fabricated electric double layer capacitor can be used as a promising device with little to no potential environmental harm.

A Crosslinked Soybean Protein Isolate Gel Polymer Electrolyte Based on Neutral Aqueous Electrolyte for a High-Energy-Density Supercapacitor.

A crosslinked membrane based on renewable, degradable and environmentally friendly soybean protein isolate was formed by solution casting method. A series of gel polymer electrolytes were prepared with the crosslinked membranes saturated with 1 mol·L−1 Li2SO4. The solid-state electric double-layer capacitors were fabricated with the prepared gel polymer electrolytes and activated carbon electrodes. The optimized solid-state supercapacitor delivered a single electrode specific capacitance of 115.17 F·g−1 at a current density of 1.0 A·g−1, which was higher than the supercapacitor assembled with the commercial separator in 1 mol·L−1 Li2SO4. The solid-state supercapacitor exhibited an outstanding cycling stability, indicating that the gel polymer electrolyte based on the crosslinked soybean protein isolate membrane could be a promising separator for a solid-state supercapacitor.

Na2so4-Polyacrylamide Neutral pH Polymer Electrolytes for Electrochemical Capacitors

Polymer electrolytes are the key enablers for solid-state electrical double layer capacitors (EDLCs) that are thin, light-weight, and flexible. Neutral pH electrolytes are particularly interesting due to their wide operating voltage window for higher energy density and non-corrosive properties for enhanced safety [1-2]. To date, polymer electrolytes comprised of Li2SO4 and polyacrylamide (PAM) have exhibited promising results [3]. However, their ionic conductivity and industrial applications are still limited by the lower mobility of Li+ ions [4] and high cost of lithium salts. Among various sulfate salts, Na2SO4 is a promising candidate as ion conductors for its higher cation mobility, relatively high solubility in water, and low cost from its earth-abundance. In this work, our objectives are to (a) develop a high-performance, low cost neutral pH polymer electrolyte using Na2SO4 and PAM, (b) understand the origin of the ionic conductivity and material properties of Na2SO4-PAM electrolytes, and (c) demonstrate its application in solid EDLC devices. Metallic cells were constructed to study the ionic conductivity, whereas cells with commercial activated carbon electrodes were fabricated to demonstrate the viability in solid EDLCs. The ionic conductivities of the polymer electrolytes with different Na2SO4:PAM ratios were tracked over 30 days period in 45 %RH storage environment (Fig. 1). The optimized electrolyte with salt-to-polymer molar ratio of 10,000:1 demonstrated a high ionic conductivity >30 mS cm-1, considerably higher than previously developed neutral pH electrolytes. With activated carbon electrodes, the polymer electrolytes enabled a stable operating 1.8 V voltage window with good cycling performance >10,000x.

Bi-functional water-born polyurethane-potassium poly(acrylate) designed for carbon-based electrodes of quasi solid-state supercapacitors: Establishing ionic tunnels and acting as a binder

In this study, a sticky copolymer of water-born polyurethane-potassium poly(acrylate) (WPU-PAAK) is designed for acting as not only a gel electrolyte but also a binder in manufacturing the carbon-based electrodes for flexible, quasi solid-state electrical double-layer capacitors (EDLCs). This copolymer has been successfully synthesized from potassium poly(acrylate) backbone cross-linked with water-born polyurethane. In comparison with the most common poly(vinylidene fluoride) (PVDF) binder, WPU-PAAK enhances the areal specific capacitance of activated carbon/carbon nanotube (AC/CNT)-coated electrode about 64% and over 100% at 1 and 10 mA cm−2, respectively. More importantly, the areal specific capacitance of AC/CNT composites with the WPU-PAAK binder is directly proportional to their mass loading, revealing the perfect utilization of active materials. The quasi solid-state device of the sandwich type demonstrates a potential window of 1.4 V and a high device-areal specific capacitance of 122.43 mF cm−2 at 1 mA cm−2. This highly flexible electrical double-layer capacitor (over 95.6% areal specific capacitance retention at a bending angle of 180°) also delivers an energy density of 33.33 μWh cm−2 at a power density of 0.7 mW cm−2 with an excellent cycle life of 87.5% retention in the 10,000-cycle test.

High performance, flexible and renewable nano-biocomposite artificial muscle based on mesoporous cellulose/ ionic liquid electrolyte membrane

A flexible nano-biocomposite artificial muscle based on a mesoporous renewable cellulose/ionic liquid (IL-Cel) electrolyte membrane with high porosity of 91.31% was developed in this paper. The IL-Cel electrolyte membrane, fabricated by a solution-phase separation process, exhibited absolute advantages in flexibility and ion transfer efficiency, so IL-Cel regenerated actuators exhibited significant enhancement in the deflection displacement and force, which were 4 and 2 times greater than traditional DMAC/Li-dissolved cellulose (Dm-Cel)-based actuators. Good flexibility (from the tensile test) and low surface resistance (within 100 Ω, from SEM) were also attained by actuators composed of an IL-Cel electrolyte membrane without regenerated substances (from FT-IR and XRD). Actuators with a solid-state electric double layer capacitor using multi-wall carbon nanotubes as electrodes and [Emim]Ac-Cel as the polymer electrolyte, exhibited the highest specific capacitance of 890 mF g−1 at 20 mV s−1, a lower internal resistance (0.098 Ω g−1) at range of 105 Hz–0.01 Hz, and the lowest power density (149 W kg−1) at 10 A g−1. Results indicated that cathode deflection was achieved by the action of van der Waals force and anion volumetric strain. These findings suggest that the developed mesoporous IL-Cel based actuators hold great promise in the further study of high-performance actuators.

High performance electrospun Li+-functionalized sulfonated poly(ether ether ketone)/PVA based nanocomposite gel polymer electrolyte for solid-state electric double layer capacitors

The synthesis of a nanocomposite gel polymer electrolytes (NGPEs) using Li+-functionalized SPEEK (SPEEK(Li)) nanofiber membrane as a matrix, cross-linked PVA as a gelled agent and LiClO4 as an electrolytic salt for electric double layer capacitors (EDLCs) were reported in this work. Compared with conventional PVA based gel electrolyte, the “SO3−Li+” functional groups and the pores structure of the SPEEK(Li) nanofiber membrane improves the ionic conductivity as well as mechanical stability, which made the prepared NGPEs exhibited a high ionic conductivity of 8.9 × 10−3 S cm−1 at ambient temperature and a large voltage stability window range from 0 to 2.0 V. The fabricated symmetric EDLCs showed a specific capacitance of 146.96 F g−1 at a current density of 0.5 A g−1, with a maximum energy density of 18.26 W h kg−1. Meanwhile, the EDLCs showed outstanding cyclical stability of 98% specific capacitance retention after 3000 cycles GCD testing, all of these results indicated that the NGPEs should be appropriate to EDLCs and next-generation energy storage systems.

Investigation of hydroxide ion-conduction in solid polymer electrolytes via electrochemical impedance spectroscopy

This study explores the conduction of hydroxide (OH−) ions in solid alkaline polymer electrolytes, and their contribution to the performance of solid-state electric double layer capacitors (EDLCs). The conductivity of tetraethylammonium hydroxide (TEAOH) polyacrylamide (PAM) and the capacitance of a solid-state EDLC based on this solid polymer electrolyte were investigated under three controlled relative humidity (RH) conditions (15, 45, and 75% RH). These properties are found to be highly dependent on the hydration structure of OH− ions that evolved in the different environments. To identify the role of hydration and ion structure in solid alkaline polymer electrolytes on device performance, dielectric analyses on the impedance spectra of TEAOH-PAM were utilized and revealed an interesting connection between the frequency dependent capacitive behaviour of the device and the ion response in the polymer electrolyte. The capacitance of EDLCs is closely related to the accumulation of ions at electrode/electrolyte interface, while the high frequency time constant for EDLCs corresponds to the transition of ion motion from vibration (energy dissipating) to translation (energy storing). Based on dielectric analysis and correlating the hydration of TEAOH-PAM with the activation energies of ionic conductivity in the three environments, we propose a framework to explain the changes of OH− ion transport in the solid-state. Under 15% RH, the segmental motion of the polymer chains facilitates the transport of TEAOH ions bound as 4:1 H2O:TEAOH crystal hydrates in the solid phase. As hydration rises under 45% RH, the segmental motion coordinates the conduction of 7.5:1 H2O:TEAOH crystal hydrates in the liquid phase. Under 75% RH, TEAOH-PAM is well hydrated and the conduction mechanism is dominated by liquid-like OH− ion-hopping of fully dissociated ions (hydration number 16.6:1). These results demonstrate the interplay of segmental motion and OH− ion-hopping in solid alkaline polymer electrolytes. The methods and findings of this study can be used to design solid aqueous polymer electrolytes with predictable long-term behaviour for inherently safe, thin, and lightweight electrochemical devices.

High-performance cellulose based nanocomposite soft actuators with porous high-conductivity electrode doped by graphene-coated carbon nanosheet

A nanocomposite soft actuator based on porous high-conductivity electrode membrane, which was composed of biopolymer cellulose mixed with chitosan and highly conductive nanoparticles generated by reduced graphene oxide encapsulated multi-walled carbon nanotube, was developed in this paper. No new substance was discovered in the regenerated electrode layer through the scanning analysis from FT-IR and XRD. Actuators exhibited significant enhancement in peak to peak displacement, which was 3.64 times increased than the traditional value at 5 V 0.1 Hz. With the test of solid-state electric double layer capacitor, actuators showed the highest specific capacitance (10.695 F g−1) at the current density of 1 A g−1, the lowest internal resistance (9.2 Ω g−1) in the frequency range of 105–10−2 Hz, and the lowest energy density (901 Wh kg−1) at the current density of 10 A g−1, which demonstrated the absolute advantages in the conductivity and channels for electrons. These findings suggest that research on porous high-conductivity electrode layer holds great promise in the further study of higher performance actuators.

Enhancing the performance of green solid-state electric double-layer capacitor incorporated with fumed silica nanoparticles

Solid polymer electrolyte (SPE) based on fumed silica nanoparticles as nanofillers, hydroxylethyl cellulose (HEC) as host polymer, magnesium trifluoromethanesulfonate salt and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid is prepared by solution casting technique. The ionic conductivity, interactions of adsorbed ions on the host polymer, structural crystallinity and thermal stability are evaluated by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Ionic conductivity studies at room temperature reveals that the SPE with 2 wt. % of fumed silica nanoparticles gives the highest conductivity compared to its counterpart. The XRD and FTIR studies confirm the dissolution of salt, ionic liquid and successful incorporation of fumed silica nanoparticles with host polymer. In order to examine the performance of SPEs, electric double-layer capacitor (EDLC) are fabricated by using activated carbon electrodes. EDLC studies demonstrate that SPE incorporated with 2 wt. % fumed silica nanoparticles gives high specific capacitance (25.0 F/g) at a scan rate of 5 mV/s compared to SPE without fumed silica. Additionally, it is able to withstand 71.3% of capacitance from its initial capacitance value over 1600 cycles at a current density of 0.4 A/g.

Electrochemical Performance of Activated Carbon Based Electric Double Layer Capacitors Using 1-Ethyl-3-Methylimidazolium Dicyanamide Ionic Liquid and Its Gel Polymer Electrolyte

The supercapacitors have emerged as an important energy storage device as they can deliver a high specific power, long cycle life, and much higher charge-discharge rates than a battery. In particular, solid-state supercapacitors have gained worldwide attention as an emerging candidate for smart and efficient energy storage devices due to the increasing demand for miniaturized electronics. Electric double layer capacitors (EDLCs) are the most widely studied class of supercapacitors which physically stores charge by forming an electric double layer at the interfaces between the high surface area carbon electrode and the electrolyte. The conventional EDLCs using high surface area activated carbon electrodes and non-aqueous liquid electrolytes represent the current state of the art. The most common cause of failure of such devices is related to the electrolyte leakage. Most of the past work on EDLCs have been carried out using the liquid electrolytes (aqueous, organic and pure ionic liquid). The gel polymer electrolytes with high ionic mobility and good dimensional/mechanical stability, offer a viable substitute for the liquid electrolytes and they are being used for flexible and solid-state electrochemical energy storage devices. Here, we report the electrochemical performance of high surface area activated carbon based EDLCs using 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA) ionic liquid and its poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) gel counterpart as electrolytes. The gel electrolyte films were prepared by immobilizing the EMImDCA ionic liquid in PVdF-HFP copolymer matrix by solution casting method. The activated carbon electrodes were prepared by mixing the activated carbon powder with conductive additive (Super C65) and PVdF-HFP binder in a ratio of 8:1:1 (w/w/w), and then the mixture was drop-casted onto a flexible thin graphite sheet which serves as current collector. The solid-state EDLC cells were fabricated by sandwiching the gel electrolyte film between two identical activated carbon electrodes whereas EDLC cells with pure IL were fabricated by using fiberglass separator soaked with IL. The EDLC cells show highly capacitive behavior as evident from the cyclic voltammogram of the cells measured at a scan rate of 20 mV s-1 which is rectangular in shape (Fig 1a). However, gel electrolyte based solid-state cell shows slightly higher resistance, obvious from slight deviation from rectangular shape at both turning potential. Typical galvanostatic charge-discharge characteristic of the EDLC cells at current density of 5 mA cm-2is shown in Fig. 1b. The linear discharge characteristics of the cell further confirms the capacitive behavior of the cells due to formation of an electric double layer at the interfaces. The EDLC cell with pure IL shows specific capacitance of ~98 F g-1 whereas IL-gel based EDLC cell shows specific capacitance of ~86 F g-1, derived from charge-discharge curves at 5 mA cm-2. A comparative performance of the EDLC cells was carried our using the impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. This paper discusses the results of these comparative studies with pure IL and its PVdF-HFP gel electrolytes. Figure 1

Thermostable gel polymer electrolyte based on succinonitrile and ionic liquid for high-performance solid-state supercapacitors

Abstract A flexible, free-standing, thermostable gel polymer electrolyte based on plastic crystalline succinonitrile (SN) and ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4) entrapped in copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) is prepared and optimized for application in solvent-free solid-state supercapacitors. The synthesized gel polymer electrolyte exhibits a high ionic conductivity over a wide temperature range (from ∼5 × 10−4 S cm−1 at −30 °C up to ∼1.5 × 10−2 S cm−1 at 80 °C) with good electrochemical stability window (−2.9 to 2.5 V). Thermal studies confirm that the SN containing gel polymer electrolyte remains stable in the same gel phase over a wide temperature range from −30 to 90 °C. The electric double layer capacitors (EDLCs) have been fabricated using activated carbon as active materials and new gel polymer electrolytes. Electrochemical performance of the EDLCs is assessed through cyclic voltammetry, galvanostatic charge-discharge cycling and impedance spectroscopy. The EDLC cells with the proper SN-containing gel polymer electrolyte has been found to give high specific capacitance 176 F g−1 at 0.18 A g−1 and 138 F g−1 at 8 A g−1. These solid-state EDLC cells show good cycling stability and the capability to retain ∼80% of the initial capacitance after 10,000 cycles.

An Approach to Solid-State Electrical Double Layer Capacitors Fabricated with Graphene Oxide-Doped, Ionic Liquid-Based Solid Copolymer Electrolytes.

Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC). The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP)-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge–discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g−1, which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application.

Solid-state electric double layer capacitors for ac line-filtering

Ultra-fast solid electric double layer capacitors (EDLCs) have been developed in both sandwich and planar interdigitated configurations using vertically-oriented graphene nanosheet (VOGN) electrodes with a hydroxide ion-conducting tetraethylammonium hydroxide (TEAOH)–polyvinyl alcohol (PVA) polymer electrolyte. These solid-state EDLCs could be scanned at a rate of 1000Vs−1 in cyclic voltammetry and demonstrated response times of less than 1ms. They retained high performance over 18 months of shelf storage and after 100,000 charge/discharge cycles with limited packaging, demonstrating the high stability of TEAOH–PVA electrolyte. The solid-state capacitors are capable of performing at elevated temperatures and have demonstrated a response time of 0.35ms at 90°C. Given their ultra-fast rate capability, excellent shelf-life and cycle life, and excellent temperature stability, these solid-state EDLCs are promising smaller and lighter alternatives to the bulky electrolytic capacitors now used for ac line-filtering.

Quaternary ammonium functionalized poly(arylene ether sulfone)/poly(vinylpyrrolidone) composite membranes for electrical double-layer capacitors with activated carbon electrodes

A series of quaternary ammonium functionalized poly(arylene ether sulfone)/poly(vinylpyrrolidone) (PAES-Q/PVP) composite membranes for separators and composite polymer electrolytes (CPEs) of electrical double-layer capacitors (EDLCs) were prepared by solution blending. EDLCs were then fabricated with the composite membranes and activated carbon electrodes. The optimized solid-state EDLC with PAES-Q/PVP composite membrane containing 40wt% PVP entrapping 6M KOH served as CPE exhibited a specific capacitance of 140.85Fg−1 and an energy density of 4.81Whkg−1 at a current density of 0.1Ag−1. Electrochemical cycle performance of the solid-state EDLC indicated almost 100% cycling retention and near 97% coulombic efficiency over 5000 charge-discharge cycles at 0.5Ag−1. Additionally, the mechanical properties, thermal stability and electrochemical performance of the composite membranes with various contents of PVP were investigated as well.

A novel poly(ethylene glycol)–grafted poly(arylene ether ketone) blend micro-porous polymer electrolyte for solid-state electric double layer capacitors formed by incorporating a chitosan-based LiClO4 gel electrolyte

A novel PAEK/PAEK-g-PEG blend MPE with a chitosan-based LiClO4 gel electrolyte was prepared and applied in an S-EDLC.