Multiwalled Carbon Nanotube Electrodes for Electrical Double Layer Capacitors with Ionic Liquid Based Gel Polymer Electrolytes

Solid-state supercapacitors with ionic liquid based gel polymer electrolyte: Effect of lithium salt addition

There is an urgent need to fulfill the hunger for energy in an efficient and a safer way. In this context, non-Lithium based energy storage devices have received a noticeable interest. A prime attention has been given on electrolytes as many of the devices are composed with liquid electrolytes which have been later identified as having various problems. Gel polymer electrolytes (GPEs) are considered as viable substituents for liquid electrolytes because they exhibit liquid like conductivities while retaining good mechanical stabilities. To further improve the safety aspects of GPEs, nowadays many studies have been performed with ionic liquids (ILs) in place of solvents on GPEs. The present study was carried out to fabricate a Zn rechargeable cell with natural graphite (NG) cathode and an IL based GPE. The IL, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF) with the polymer poly(vinyl chloride) (PVC) and the salt zinc trifluoromethanesulfonate (Zn(CF3SO3)2 – ZnTF) were used in preparing the GPE. The electrochemical properties of the GPE were evaluated using electrochemical impedance spectroscopy (EIS) and DC polarization test. The maximum room temperature conductivity of the electrolyte was 3.06 × 10-4 S cm-1. Conductivity of the electrolyte was highly contributed by ions. The cell of the configuration, Zn / GPE / NG was characterized using cyclic voltammetry (CV) test. Initial specific charge was about 2.25 mA h g-1 and during 50 cycles, it had reduced down to 2.15 mA h g-1. Moreover, satisfactory stability was observed during CV test. Further studies are in progress to improve the cell performance.

Performance of an ionic liquid based gel polymer electrolyte and its application in a redox capacitor

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 $$^{-1}$$ .

We report the preparation of a gelled form of multiwalled carbon nanotubes (MWCNTs) with an ionic liquid 1-butyl-1-methyl pyrrolidinium bis(trifluoromethane sulfonyl)imide (BMPTFSI)), referred to as ‘bucky gel’, to be used as binderless electrodes in electrical double layer capacitors (EDLCs). The characteristics of gelled MWCNTs are compared with pristine MWCNTs using transmission electron microscopy, x-ray diffraction and Raman studies. A gel polymer electrolyte film consisting of a blend of poly(vinylidene fluoride-co-hexafluoropropylene) and BMPTFSI, exhibiting a room temperature ionic conductivity of 1.5 × 10−3 S cm−1, shows its suitability as an electrolyte/separator in flexible EDLCs. The performance of EDLCs, assembled with bucky gel electrodes, using impedance spectroscopy, cyclic voltammetry and charge–discharge analyses, are compared with those fabricated with pristine MWCNT-electrodes. An improvement in specific capacitance (from 19.6 to 51.3 F g−1) is noted when pristine MWCNTs are replaced by gelled MWCNT-binderless electrodes. Although the rate performance of the EDLCs with gelled MWCNT-electrodes is reduced, the pulse power of the device is sufficiently high (∼10.5 kW kg−1). The gelled electrodes offer improvements in energy and power densities from 2.8 to 8.0 Wh kg−1 and 2.0 to 4.7 kW kg−1, respectively. Studies indicate that the gel formation of MWCNTs with ionic liquid is an excellent route to obtain high-performance EDLCs.

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

Outstanding features of alginate-based gel electrolyte with ionic liquid for electric double layer capacitors

Polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyacrylonitrile (PAN) based gel electrolytes with a mixture of ethylene carbonate and propylene carbonate as plasticizer and lithium perchlorate were used to fabricate an electric double‐layer capacitor (EDLC). The performance of EDLCs with these gel electrolyes was investigated by using isotropic high‐density graphite electrodes. The ion conductivities of various gel electrolytes were of the order of 10−4 to 10−3 S cm−1, and they decreased in the order PAN > PEO > PMMA at ambient temperature. Capacitances approaching the value of EDLCs using organic liquid electrolyte, 20 mF cm−2, with an isotropic high‐density graphite electrode were obtained in PAN and PMMA gel electrolytes. The EDLC with PMMA‐based gel electrolyte showed good charge‐discharge behavior over 104 cycles at a charge potential of 3.0 V.

ABSTRACTPolymer gel electrolytes consisting of poly(vinylidene fluoride) (PVdF), tetraethylammoniumtetrafluoroborate (TEABF4), and propylene carbonate (PC) as a plasticizer have been investigatedfor electric double layer capacitors. The PVdF gel electrolytes showed high ionic conductivity (ca.6 mS cm-1at 298 K). To assemble model capacitors with the PVdF gel electrolytes and activatedcarbon fiber cloth electrodes, a pair of the fixed electrodes was soaked in a precursor solutioncontaining PC, PVdF, and TEABF4, followed by evaporation of the PC solvent in a vacuumoven. The resulting gel electrolytes were in good contact with the electrodes. The modelcapacitors with the PVdF gel electrolytes showed a large value of capacitance and high coulombicefficiency in operation voltage ranges of 1–2 and 1–3 V. It is worth noting that the capacitors withthe PVdF electrolytes showed long voltage retention in a self-discharge test. These goodcharacteristics of our gel capacitors were comparable to those of typical double layer capacitorswith a liquid organic electrolyte containing PC and TEABF4; rather, the voltage retentivity of thePVdF gel capacitors was much superior to that of the capacitors with the organic electrolyte.

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

Acetylene black/poly(vinylidene fluoride) gel electrolyte composite electrode for an electric double-layer capacitor

This study demonstrated that electrical double layer capacitors (EDLC) can be fabricated using Ge electrodes and ionic liquids. We found that the ionic liquids must be dried for the use of electrolytes of the EDLCs because water causes chemical reaction with Ge. This chemical reaction is, however, useful to make porous structures on the Ge to prepare large surface area electrodes essential to the EDLCs. In addition, ionic liquid used for the chemical reaction can fill the complex Ge pores. Based on these findings, we prepared the EDLCs composed of Ge porous electrodes and the ionic liquid electrolyte. By drying the ionic liquid at 100 °C, the device showed reasonable electrochemical behavior as the EDLCs.

Ionic liquids containing the tetrafluoroborate anion have the best performance and stability for electric double layer capacitor applications

Electric double layer capacitors with gelled polymer electrolytes based on poly(ethylene oxide) cured with poly(propylene oxide) diamines

This paper proposes a cyanide-containing polymer as the framework of gel electrolytes for electric double layer capacitors (EDLCs). Dielectric studies in a frequency range of 101-105 Hz demonstrate the fast polarization and low dielectric loss features of the gel electrolyte that entraps 1-M TEABF4/PC. The swift polarization of the gel electrolyte can be attributed to the high dipole moment of the contained cyanide functionality on the polymer chains. When supported with separator membranes, the ionic conductivity of the gel electrolyte is one order of magnitude higher than that of the 1-M TEMABF4/PC liquid electrolyte (10-2 S cm-2 vs. 10-3 S cm-2 at room temperature) owning to the presence of polarizable cyanide groups, which facilitate ion motion under the action of an applied electric field. In addition, the polymer framework improves the dissociation of ion-complexes to promote ion transport. Symmetric EDLCs assembled using the gel electrolyte exhibits specific capacitances of 199 and 130 F g -1 (within 0-2.7 V) at galvanostatic discharge rates of 0.5 and 100 A g-1, respectively, based on the carbon mass. The corresponding capacitances for liquid-electrolyte EDLCs are 172 and 109 F g-1. The gel EDLCs exhibit high stability, retaining ~95% of their initial capacitance after 20,000 cycles. An important feature of this gel electrolyte is its controllable gelling time. The electrolyte can be used in a manner similar to that of an ordinary liquid electrolyte during assembly and auto-gelation of the electrolyte subsequently takes place in the assembled EDLC. The implemented auto-gelation greatly enhances the durability of the resulting devices and is applicable in a wide range of energy storage systems. Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, and 106-3113-E-006-009) and by the Ministry of Education’s Aim for the Top University Project at National Cheng Kung University, Taiwan.