Glutaraldehyde-Glyoxal Co-crosslinked Gelatin Hydrogel Electrolytes with KI/HQ Dopant for Solid-State Electric Double Layer Capacitors

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.

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

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

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

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.

The comparative performance of the solid-state electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and poly (vinaylidinefluoride-co-hexafluoropropyline) (PVdF-HFP) based gel polymer electrolytes (GPEs) containing potassium and lithium salts have been studied. The room temperature ionic conductivity of the GPEs have been found to be ∼3.8×10−3 and 5.9×10−3 S cm−1 for lithium and potassium based systems. The performance of EDLC cells studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques, indicate that the EDLC with potassium salt containing GPE shows excellent performance almost equivalent to the EDLC with Li-salt-based GPE.

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

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

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

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.

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

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

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.

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.

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.