Quasi‐Solid‐State Supercapacitor Using Redox Additive

Electrical double layer capacitor using poly(methyl methacrylate)–C4BO8Li gel polymer electrolyte and carbonaceous material from shells of mata kucing (Dimocarpus longan) fruit

The fundamental understanding of the relationship between ion transport and segmental dynamics of polymer chains in polymer electrolytes is crucial for achieving high ionic conductivity at room temperature for technological applications in supercapacitors, batteries, etc. In this work, the ion dynamics and relaxation have been studied for gel polymer electrolytes (GPEs) containing P(VdF-HFP) as host polymer, adiponitrile as a plasticizer, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as ionic liquid, and diphenylamine and copper iodide redox additives as fillers. The crystallization temperature of the ionic liquid and the melting temperature of the plasticizer play important roles in ion dynamics. The highest room-temperature ionic conductivity (3.3 × 10−3 S/cm) was obtained for the GPE filled with dual redox additives. The broadband ac conductivity spectra have been analyzed by using the Universal Power law model coupled with the Poisson–Nernst–Planck (PNP) model. The solid–solid phase transition of the ionic liquid affects the grain and grain boundary regions of the GPEs due to the presence of redox fillers. The temperature dependence of the dielectric spectra of the GPEs containing redox fillers confirms the phase transition at the crystallization temperature. The electric modulus and dielectric spectra have been analyzed by using the Havrilliak–Nigami, Kohlrausch–Williams–Watts, and derivative dielectric constant functions. The scaling of ac conductivity and modulus spectra confirms a common ion conduction and relaxation mechanism for the GPEs. The influence of dual redox additives is clearly observed in the values of ionic conductivity, ion diffusivity, and relaxation time.

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.

In this work, polyvinyl alcohol (PVA)-salt gel polymer electrolytes (GPE) have been prepared with ethylene carbonate (EC) and propylene carbonate (PC) dissolved in dimethyl sulfoxide (DMSO). Potassium iodide (KI) and tetrapropyl ammonium iodide (TPAI) salts have been used to provide the conducting ions. The single salt system (containing KI only) with composition 15.20 wt. % PVA - 31.73 wt. % KI - 22.67 wt. % EC - 30.40 wt. % PC has the highest room temperature conductivity of 1.25 × 10-2 S cm-1. With addition of TPAI, conductivity of 9.79×10-3 S·cm-1 has been obtained for 15.21 wt. % PVA - 15.86 wt. % KI - 15.86 wt. % TPAI - 22.67 wt. % EC - 30.40 wt. % PC and is the highest conducting electrolyte in the binary salt system. The dye-sensitized solar cell (DSSC) using the electrolyte with only KI salt exhibits an efficiency of 2.64% whereas DSSC utilizing binary salt electrolyte system has efficiency of 3.12%.

Redox additives dependent supercapacitor performances of ZnO/SnO2@MWCNT nanocomposites

Polymer gel electrolyte (PGE) film is prepared by incorporating polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) as polymer, ethylene carbonate (EC)-propylene carbonate (PC) as plasticizers and tetraethylammonium tetrafluoroborate ( $$\hbox {TEABF}_{4}$$ ) as salt using solution cast technique. By varying weight percentages of EC-PC- $$\hbox {TEABF}_{4}$$ into a host polymer, different samples of PGE were prepared, and the concentration of EC-PC- $$\hbox {TEABF}_{4}$$ was optimized for maximum conductivity, and stability of the prepared film. The maximum ionic conductivity of the order of $$4.9\times 10^{-3}\,\hbox {S cm}^{-1}$$ was determined for 80 wt% of [EC-PC (1:1 v/v)- $$\hbox {TEABF}_{4}$$ (1.0 M)]. From the conductivity as a function of temperature, activation energy $${E}_{\mathrm{a}}$$ was calculated and it is about 0.06 eV. Overall, the amorphous structure was confirmed by X-ray diffraction analysis. Dielectric and impedance spectroscopic analysis was also carried out to understand the electrical behaviour of electrolyte using modified Debye’s function. An ionic character of prepared electrolyte was confirmed from DC polarization method. The ionic transference number of 0.91 was calculated from the data while the electrical potential stability window was found to be 3.8 V. The electrical performance of prepared PGE was examined by fabricating electrical double-layer capacitor (EDLC). In a supercapacitor, commercially procured activated carbon electrodes were employed. The specific capacitance of EDLC cell is found to be $$\sim $$ 60 mF cm $$^{-2}$$ , and equivalent single-electrode capacitance is about 39 F g $$^{-1}$$ .

Synthesis and electrochemical properties of lithium methacrylate-based self-doped gel polymer electrolytes

Solid state redox capacitors have received a tremendous interest in terms of several characteristics such as their fast energy delivery, short charging time, high power density and extended durability. Due to the absence of a liquid electrolyte, they are free from drawbacks of leakage and unsafe. In this study, preparation and characterization of a redox capacitor consisting with two identical polypyrrole (PPy): dodecylbenzenesulfonate (DBS) electrodes and a gel polymer electrolyte (GPE) based on polyvinylidene fluoride (PVdF), ethylene carbonate (EC), propylene carbonate (PC) and sodium thiocyanate (NaSCN) is reported. The GPE having the composition, 0.4 PVdF: 1 EC: 1 PC: 0.075 NaSCN (by weight) showed the maximum conductivity of 2.25× 10-3 S cm-1. Redox capacitors were characterized using Cyclic Voltammetry, Electrochemical Impedance Spectroscopy and Galvanostatic Charge Discharge test. They exhibited an energy density about 0.25 W h kg-1 and an average power density of 4 kW kg-1.

Electrochemical redox supercapacitors using PVdF-HFP based gel electrolytes and polypyrrole as conducting polymer electrode

Gel polymer electrolytes (GPEs) were prepared by dissolving lithium tetrafluoroborate (LiBF4) salt, poly(methylmethacrylate) (PMMA) polymer and distinct non-volatile solvents propylene carbonate (PC), and -N,N-dimethylformamide (DMF) in single as well as binary solvent mixtures. Ionic conductivities of 8.93 mS/cm and 6.68 mS/cm at 25 °C have been obtained for gel polymer electrolytes for 10 wt% PMMA in the solution of LiBF4 in binary solvent mixture of PC:DMF in (1:1) and (2:1) volume ratios respectively. The dispersion of nano-sized silica in gel polymer electrolyte not only exhibits small change in ionic conductivity but also enhances the mechanical strength as well as viscosity of gel polymer electrolytes. At room temperature, the ionic conductivity has been found to be 8.00 mS/cm for 6 wt% nano-sized silica in GPEs. Fourier-transform infrared (FTIR) spectroscopic studies have been used to scrutinize the corroboration of the complexation between PMMA, LiBF4, PC, DMF, PC:DMF, and SiO2. The interactions between salt and solvents in liquid electrolytes have also been analyzed by FTIR spectroscopy illustrating the strong interaction between lithium salt and solvent molecules. The appearance/disappearance and shifting of some peaks confirm the interaction among the constituents of nano-dispersed gel polymer electrolytes. The mechanical strength was confirmed by dynamic mechanical analysis (DMA) and viscosity [ηPC:DMF (2:1) > ηPC:DMF (1:1) > ηPC] for nano-dispersed silica-based gel polymer electrolytes. The electrical and mechanical stability with high ionic conductivity for such gel polymer electrolytes makes these electrolytes suitable for many device applications like high energy density lithium-ion batteries, super-capacitors, electro-chromic devices etc.

Propylene carbonate-nitrile solvent blends for thermally stable gel polymer lithium ion battery electrolytes

Multiwalled carbon nanotube (MWCNT) based electrical double-layer capacitors (EDLCs) using ionic liquid incorporated magnesium ion conducting gel polymer electrolytes were constructed and characterized. For comparison, three electrolytes were used to fabricate EDLCs comprised of a room-temperature ionic liquid 1-ethyl-3-methyl-imidazolium trifluoromethanesulfonate (EMITf) or a solution of magnesium salt (magnesium trifluoromethanesulfonate or Mg triflate) in EMITf or a solution of magnesium salt in the mixture of EMITf and a cosolvent of ethylene carbonate (EC):propylene carbonate (PC), immobilized with poly(vinylidene fluoride-hexafluoropropylene). The comparative performance characteristics of the EDLCs based on impedance analysis, cyclic voltammetry, and galvanostatic charge–discharge tests for numerous cycles were presented. The role of magnesium ions and the EC:PC cosolvent incorporated in the gel electrolytes was important in the dramatic improvement of the EDLCs’ performance. The optimum capacitance value of (equivalent to the single electrode specific capacitance of of MWCNTs) was achieved for the EC:PC and the ionic liquid incorporated gel electrolyte based EDLCs. This corresponded to the specific energy of and the high value of power density of . The EDLCs showed excellent cyclic performances for or even more.

Nanocomposite polymer gel with dispersed alumina as an efficient electrolyte for application in supercapacitors

The strategy of using redox additive electrolyte in combination with multiwall carbon nanotubes/metal oxide composites leads to a substantial improvements in the specific energy and power of asymmetric supercapacitors (ASCs). When the pure electrolyte is optimally modified with a redox additive viz., KI, ~105% increase in the specific energy is obtained with good cyclic stability over 3,000 charge-discharge cycles and ~14.7% capacitance fade. This increase is a direct consequence of the iodine/iodide redox pairs that strongly modifies the faradaic and non-faradaic type reactions occurring on the surface of the electrodes. Contrary to what is shown in few earlier reports, it is established that indiscriminate increase in the concentration of redox additives will leads to performance loss. Suitable explanations are given based on theoretical laws. The specific energy or power values being reported in the fabricated ASCs are comparable or higher than those reported in ASCs based on toxic acetonitrile or expensive ionic liquids. The paper shows that the use of redox additive is economically favorable strategy for obtaining cost effective and environmentally friendly ASCs.

Poor conductivity and toxic technological garbage of polymer electrolyte has delayed energy storage application in electric vehicles. Biodegradable gel polymer electrolytes (GPEs) based on poly (e-caprolactone) (PCL) are prepared. PCL is used to immobilize liquid electrolyte containing lithium bis(trifluoromethanesulfonyl) imide, ethylene carbonate, and propylene carbonate. Impedance spectroscopy, X-ray diffraction, and differential scanning calorimetry are used to characterize the ionic conductivity and structural and thermal properties of GPEs, respectively. For jelly-like GPEs, it exhibits liquid-like ionic conductivity of 1.69 × 10−3 S cm−1 at room temperature with a composition ratio (PCL:LiTFSI:EC:PC) of (22.5:7.5:35:35) (w/w). Results show that the polymer matrix forms cross-linked network within the liquid electrolyte, acting like an adhesive to hold the high fluidity liquid molecules. In temperature dependence studies, the GPEs are observed to obey Arrhenius equation indicating that ion transport occurs via hopping mechanism. The findings in XRD and DSC are in good agreement with conductivity results.