High-Energy-Density Carbon Supercapacitors Incorporating a Plastic-Crystal-Based Nonaqueous Redox-Active Gel Polymer Electrolyte

Abstract

Addition of redox additives in electrolytes to enhance the electrochemical activity at electrode–electrolyte interfaces is one of the prime approaches these days to develop high-energy-density supercapacitors. Here, we report an investigation on a quasi-solid-state supercapacitor, fabricated with a nonaqueous, gel polymer electrolyte (GPE) based on a mixture of a plastic crystal succinonitrile and an ionic liquid 1-butyl-1-methylpyrrolidinium bis­(trifluoromethyl sulfonyl) imide, added with a redox additive hydroquinone (HQ), immobilized in a polymer poly­(vinylidine fluoride-co-hexafluoropropylene). The HQ-incorporated GPE is observed to be a freestanding, easily processible, and reusable film, showing excellent flexibility and thermal stability up to ∼100 °C. The high ionic conductivity (∼4.2 mS cm–1) and wide electrochemical stability window (∼5.0 V) through linear sweep voltammetry measurements make the optimum composition of GPE a potential electrolyte for high-energy-density supercapacitors. The symmetric supercapacitor coin cells have been fabricated with peanut shell-derived porous carbon electrodes separated by GPE films. The electrochemical activity due to the presence of HQ at carbon electrode–GPE interfaces introduces additional pseudocapacitance over the double-layer capacitance, leading to enhanced overall specific capacitance (289 F g–1), and hence corresponds to the high specific energy (∼40 Wh kg–1) and maximum power (∼20 kW kg–1). The capacitor cell shows prolonged cyclic profile up to ∼10 000 charge–discharge cycles with ca. 85–93% Coulombic efficiency.

Ionic Liquid‐Based Redox Active Electrolytes for Supercapacitors

“…Therefore, the development of IL-RE-based GPEs will be a promising direction for the flexible/solid SCs with high energy density. [142,143]…”

High-Energy-Density 3.5 V Carbon Supercapacitor Fabricated with Ionic-Liquid-Incorporated Redox-Active Gel Polymer Electrolyte

“…[11][12][13]62 To overcome many such issues and to enhance the electrochemistry of supercapacitors, ionic liquid (IL)-containing GPEs are available in many recent reports. 11,12,[17][18][19][20][21][29][30][31][32][33][34][35][36][37][38]53 ILs, when used in the pure form or added with an appropriate amount of suitable salts, basically show attractive features as electrolytes due to their higher ionic conductivities, wider ESWs, nonvolatility, and nonflammability. [11][12][13]32 Several nonaqueous redox-active IL-based liquid electrolytes were recently reported for high-performance supercapacitors.…”

“…The IL-based redox-active GPEs are rarely reported, including a few reports by our group. 29,35−38 These includes various systems, namely, PVdF-HFP/BMITFSI/ NaI, 35 PVdF-HFP/BMITFSI/KI, 36 PVdF-HFP/BMITFSI/ DPA, 36 PVdF-HFP/BMITFSI/DPA/KI, 36 PVdF-HFP/ EMITFSI/KI, 37 PVdF-HFP/BMPTFSI/SN/HQ, 38 PVA/ PVP/EMIHSO 4 /HQ, 29 PVdF-HFP/BMITFSI/EC/TEMPO/ p-BQ, 47 PVA/Na 2 SO 4 /Pyr 14 Br, 30 and so forth.…”

Solar-Powered Supercapacitors Integrated with a Shared Electrode

“…Solar-powered integrated supercapacitors (SPISs), also known as self-powered systems or photo-rechargeable systems, are becoming more widely applied in aerospace, smart buildings, and soft robotics. − A typical SPIS is formed by simply integrating two devices, an energy-harvesting element and an energy-storage device, using an external power connection. , In a frequently used SPIS configuration, a supercapacitor (SC) is integrated with an organic solar cell (OSC) into one unit that stores the electric energy produced by the solar power and is able to supply continuous energy under light illumination. Inverted OSCs ( i OSCs) have become leading candidates for the energy-harvesting elements in SPISs, being solution-processable and lightweight and having adequate capacity and excellent compatibility in connecting to other functional devices. − High-power SCs are the electric-storage elements in SPISs and able to effectively collect the output of solar cells under intermittent sunlight. , An integrated system with both an i OSC and an SC is called an organic solar supercapacitor (OSSC) and has potential for future SPIS designs . However, their tedious fabrication process and large size lead to energy dissipation and waste of power .…”

“…7−9 High-power SCs are the electric-storage elements in SPISs and able to effectively collect the output of solar cells under intermittent sunlight. 10,11 An integrated system with both an iOSC and an SC is called an organic solar supercapacitor (OSSC) and has potential for future SPIS designs. 12 However, their tedious fabrication process and large size lead to energy dissipation and waste of power.…”