Ionic Liquid Based Gel Electrolyte Research Articles

Enhancing EDLC applications with [BMIM]BF4-integrated cellulose gel electrolyte for sustainable energy storage

Researchers worldwide have extensively carried out the fabrication of supercapacitors using ionic liquid-based gel electrolytes. Gel polymer electrolytes (GPEs) are an excellent alternative electrolyte due to their high ionic conductivity and lack of safety issues associated with solid and liquid polymer electrolytes. This work highlights the performance of a GPE composed of 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM]BF4 mixed with ammonium nitrate (NH4NO3) as the charge carrier, entrapped in methylcellulose (MC) for its application as an electrolyte in supercapacitors. The results of the Fourier transform infrared spectroscopy (FTIR) study are in good agreement with the literature, confirming the interaction between the materials observed through the shifting of the hydroxyl band. Moreover, the addition of [BMIM]BF4 successfully reduced the degree of crystallinity and crystallite size, thus enhancing the amorphous region of the electrolytes, as observed in the X-ray diffraction (XRD) diffractogram. The sample with 10 wt% [BMIM]BF4 (IL10) exhibits the highest ambient conductivity of (2.44 ± 0.36) × 10−2 S cm−1. The obtained ionic transference number (tion) of 0.98 confirms that ions are the dominant charge carriers. Considering its electrochemically stability up to 2.6 V within a potential range of 3.0 V, the IL10 electrolyte was chosen as a separator for application in an electric double-layer capacitor (EDLC). The EDLC is characterized via cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis.

Highly efficient and stable ionic liquid-based gel electrolytes.

Gel electrolytes are promising candidates for dye-sensitized solar cells (DSSCs) and other devices, but the ways to obtain stable gels always result in sacrifice of their ionic conductivity. This contradiction seriously limits the practical application of gel electrolytes. Herein, a new design strategy using rich carboxylic group-modified silica nanoparticles (COOH-SiO2) with a branched, well-organized framework to develop ionic liquid-based gel electrolytes possessing high conductivity is demonstrated. The branched network of COOH-SiO2 and the strong interaction in electrolytes result in the effective solidification of ionic liquids. Moreover, adding COOH-SiO2 to ionic liquid electrolytes contributes to salt dissociation, decreases the activation energy, and improves the charge transport and recombination characteristics at the electrolyte/electrode interface. DSSCs fabricated with COOH-SiO2 nanoparticles deliver a higher short-circuit photocurrent density (Jsc) than the reference cell. A maximum efficiency of 8.02% with the highest Jsc value of 16.60 mA cm-2 is obtained for solar cells containing 6 wt% COOH-SiO2.

Synergistic effect of electrolyte additives on the improvement in interfacial stability between ionic liquid based gel electrolyte and LiFePO4 cathode

Polyethylene (PE)-supported poly (vinylidene fluoride)-hexafluoropropene P(VdF-HFP) based GPE was prepared by using ionic liquid 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) as solvent, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as lithium salt, vinylene carbonate (VC) and lithium bis(oxalato)borate (LiBOB) as CEI (solid electrolyte interface formed between cathode and electrolyte) film-forming additive. The performance of ionic liquid type GPE with VC and LiBOB additives was understood by electrochemical impedance spectroscopy, linear sweep voltammetry, charge/discharge test, scanning electron microscope, transmission electron microscope, X-ray diffraction and inductively coupled plasma. It was found that the ionic liquid based GPE with 5 wt% VC and 1.5 wt% LiBOB as additives helped to improve the interfacial stability by forming superior quality of CEI layer on the surface of LiFePO4 cathode. Thinner and more uniform CEI layer built by the synergistic effect of additives, which VC contributed to a soft organic layer, while LiBOB facilitated the formation of a brittle and tough inorganic layer, could inhibit the further dissolution of Fe ion and keep the structural integrity of LiFePO4. Caused by the preferably comprehensive performance of ionic liquid based GPE, in which exhibited good compatibility with lithium anode, and the improved oxidative potential of 5.4 V, the Li/GPE/LiFePO4 coin cell showed excellent cyclic stability, maintaining 96.7% of its initial discharge capacity after 100 cycles at 0.1C rate, compared to that of 72.3% for the GPE without additive.

Tungsten Oxide Nanofibers for Electrochromic Device Application

The tungsten oxide (WO3) nanofibers were grown directly onto an ITO-coated glass via an electrospinning method for electrochromic applications. The electrochromic properties of WO3 nanofibers were investigated in the presence of different electrolytes including a series of ionic liquids and classic LiClO4-PC system. A significant optical modulation of 20.82% at 760 nm, reversible coloration with efficiency of 64.58 cm2/C and excellent cycling stability were achieved for the nanofiber electrochromic device (ECD) with ionic liquid based gel electrolyte.

Synthesis and optimization of new polymeric ionic liquid poly(diallydimethylammonium) bis(trifluoromethane sulfonyl)imde based gel electrolyte films

Polymeric ionic liquid-based gel electrolyte films are a new generation of electrolyte materials for flexible energy storage device applications. In this work, Li-ion conducting gel electrolyte films are prepared with the polymeric ionic liquid poly(diallydimethylammonium) bis(trifluoromethane sulfonyl)imide (poly(DADMATFSI)) as the host polymer and the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt as the dopant. The crystalline nature, thermal stability, ionic conductivity and electrochemical stability window of the polymeric electrolyte films are analyzed by various characterization techniques. It is found that the polymeric electrolyte films exhibit high flexibility and excellent thermal stability. Their room-temperature electrical conductivity increases with increasing LiTFSI concentration and reaches a high value of 1.00 × 10−3 S cm−1 at 20 wt% LiTFSI. The ionic transference numbers of the polymeric electrolyte films are in the range of 0.98–0.99, indicating that they are perfect ion conductors. Finally, the electrochemical stability window of the 20 wt% LiTFSI-doped polymeric electrolyte film is determined as approximately 6 V, which is a promising value for flexible energy storage device applications.

Effect of organic solvent addition on electrochemical properties of ionic liquid based Na+ conducting gel electrolytes

A novel sodium ion conducting gel polymer electrolyte comprising room temperature ionic liquid, 1-ethyl 3-methyl imidazolium trifluoro-methane sulfonate (EMITf) incorporated with ethylene carbonate and propylene carbonate and its solution with sodium trifluoromethane sulfonate (NaTf) entrapped in poly(vinylidinefluoride-co-hexfluoropropylene) (PVdF-HFP) is prepared using solution cast technique. The gel electrolyte is obtained in the form of free-standing transparent film. The gel electrolyte offers electrical conductivity of ∼10−3Scm−1 at ∼30°C with good mechanical, thermal and electrochemical stability window. The electrical conductivity is measured as a function of temperature and found to be consistent with Vogel-Tamman-Fulcher (VTF) relationship in the temperature range from 30°C to 75°C.Sodium ion conduction in the gel electrolyte film is confirmed from cyclic voltammetry and transport number measurements. The value of the sodium ion transport number of the ionic liquid based gel electrolyte is ∼0.19. The sodium sulfur battery with the gel electrolytes delivers the first discharge capacity of 267mAhg−1 sulfur and then it decreases with repeated charge–discharge cycles.

3 V omni-directionally stretchable one-body supercapacitors based on a single ion–gel matrix and carbon nanotubes

Stretchable supercapacitors often have laminated structures consisting of electrode, electrolyte, and supporting layers. Since the layers are likely to be composed of different materials, delamination is a major cause of failure upon stretching. In this study, we demonstrate delamination-free stretchable supercapacitors where all the component layers are prepared with a single matrix, which is composed of a polymer, poly(vinylidene fluoride-hexafluoropropylene) and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Since the ionic liquid in the composite plays a role as both an electrolyte and a plasticizer, this composite can be used as an electrolyte and a supporting layer in the stretchable supercapacitor. The electrode layer can be fabricated by incorporating carbon nanotubes in the common matrix. Then, all the layers can be seamlessly fused into one body by dissolving the surface of the composite with acetone, which evaporates after the integration, leaving no borders between the layers. This one-body stretchable supercapacitor not only has high durability against repetitive stretches but also is stretchable in all directions. This feature clearly distinguishes them from conventional stretchable supercapacitors fabricated using buckled structures, which are stretchable only in one or two directions. Moreover, this supercapacitor has high cell voltage (∼3 V) owing to the ionic liquid-based gel electrolytes. Our demonstration of isotropically stretchable high-durability supercapacitors may have a great implication in the development of stretchable energy storage devices for real applications.

Electrochromic device based on electrospun WO3 nanofibers

The tungsten oxide (WO3) nanofibers were grown directly onto an ITO-coated glass via an electrospinning method for electrochromic applications. The electrochromic properties of WO3 nanofibers were investigated in the presence of different electrolytes including a series of ionic liquids and classic LiClO4-PC system. A significant optical modulation of 20.82% at 760nm, reversible coloration with efficiency of 64.58cm2/C and excellent cycling stability were achieved for the nanofiber electrochromic device (ECD) with ionic liquid based gel electrolyte.

Low-Dose Imidazolium Cation Grafted Polymeric Nanotubes for Quasi-solid-state Dye-sensitized Solar Cells

Poly(divinybenzene-co-chloromethylstyrene) (poly(DVB-co-VBC)) nanotubes (PDVBVBC-NT) and imidazolium surface functionalized poly(DVB-co-VBC) (Im-PDVBVBC-NT) are synthesized by cationic polymerization and utilized as the gelators for ionic liquid based gel electrolytes. Compared with the synthesized pristine PDVBVBC-NT, Im-PDVBVBC-NT (a gelator dose as low as 1 wt%) based gel electrolytes show higher ionic conductivity and diffusion coefficient. The fabricated DSSCs based on Im-PDVBVBC-NT gel electrolyte show a power conversion efficiency of 4.9% and 5.5% under a simulated air mass 1.5 solar spectrum illumination at 100 mW cm−2 and 50 mW cm−2, respectively. Furthermore, Im-PDVBVBC-NT based DSSCs show better long-term stability than that with ionic liquid electrolyte, which indicated that Im-PDVBVBC-NT based gel electrolytes could overcome the leakage problems of the cells with pure ionic liquid electrolytes.

A new organo-inorganic hybrid of poly(cyclotriphosphazene-4,4′-bipyridinium)chloride with a large electrochromic contrast

A new organo-inorganic hybrid electrochromic material poly(cyclotriphosphazene-4,4′-bipyridinium)chloride salt was synthesized wherein each phosphorus atom in the triphosphazene core is linked by diquaternized 4,4′-bipyridyls (PPBP). The electrochrome was characterized by 31P nuclear magnetic resonance, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS confirmed the formation of P–N+ and P–N linkages in the PPBP and the conversion of covalently bound Cl to ionic Cl− species. The transparent PPBP material undergoes three reversible one electron-transfer reactions to yield a radical cation insoluble film which first acquires a purple hue and then turns deep blue. Electrochromic devices were constructed with the PPBP hybrid dissolved in a highly conductive, thermally stable and electrochemically inert ionic liquid based gel electrolyte and a Prussian blue (PB) layer as the anode. The PPBP–PB device showed an extremely large coloration efficiency of 504 cm2 C−1, an exceptionally high transmission modulation of 70.5% at 590 nm, one among the highest reported contrasts in organic electrochromics, a large reflectance contrast of 59.2% at 545 nm and fast switching kinetics. The device was durable as it retained 96.2% of its original transmission after 1000 color-bleach cycles, thus exemplifying its use for both reflective and transmissive electrochromic applications. Electrochemical impedance studies revealed charge transfer to be a less resistive process during reduction relative to oxidation which cumulatively ensues in shorter coloration times. Our studies demonstrate the yet untapped potential of the inorganic (PNCl2)3 in steering the synthesis of new organo-inorganic hybrid materials, capable of undergoing facile redox phenomena, manifesting in unequalled functional properties and thereby offering opportunities to use this trimer for preparing a whole gamut of new high performance electroactive compounds.

Reclamation and reuse of ionic liquids from silica-based ionogels using spontaneous water-driven separation

Ionic liquids (ILs) are widely regarded as “green” materials, partially because they are assumed to be recyclable in most applications. Here, the effectiveness of a water-based IL reclamation process with low energy requirements is demonstrated using two types of silica-supported ionic liquid-based gel electrolytes (ionogels) incorporating a variety of common ionic liquids. More than 90% of the IL can be separated from the ionogel silica scaffold simply by submerging the ionogel in water, with no additional energy input. It is posited that water is able to compete with the hydrophobic IL for access to the hydrophilic silica scaffold surface, liberating the IL from the ionogel structure. Spontaneous water-based separation leads to the recovery of at least 70% of the original IL mass; transfer losses experienced at the laboratory scale are expected to decrease with process scale-up. Recovered ILs exhibit similar electrical performance to the virgin materials in a double layer capacitor structure.

A novel thixotropic and ionic liquid-based gel electrolyte for efficient dye-sensitized solar cells

A novel thixotropic composite electrolyte was fabricated by using the amine group-functionalized silica nanoparticles as the gelator of an ionic liquid-based electrolyte for dye-sensitized solar cells. The SEM image of electrode deposited with electrolyte confirms that the high viscous gel electrolyte has a good contact with TiO2 electrode ascribed to the thixotropic property of the electrolyte. Based on the thixotropic and ionic liquid based-electrolyte containing the amine group-functionalized silica particles, the cells show better performance owing to the increased open-circuit voltage than that of the liquid device, yield a high energy conversion efficiency of 6.69% under AM 1.5 illumination at 100mVcm−2 when the content of the amine group-functionalized silica is 15wt.% and exhibit a long-term stability without sealing.

Electrochromic device response controlled by an in situ polymerized ionic liquid based gel electrolyte

Polymer electrolytes were synthesized by two different approaches and applied to electrochromic devices based on electrodeposited tungsten oxide (WO3) or poly(3,4-ethylenedioxythiophene) (PEDOT) films as the cathode, and a Prussian blue (PB) film as the anode. The first method involved the entrapping of an ionic liquid in a polymer host (poly(methylmethacrylate) or PMMA) and the second approach relied on the in situ thermal polymerization of methylmethacrylate (MMA) in the hydrophobic ionic liquid, yielding a solidified transparent gel. The effect of in situ solid polymer electrolyte formation on device performance characteristics was realized in terms of a larger coloration efficiency of 119 cm2 C−1 (λ = 550 nm) achieved for the WO3–PB (MMA) device, as compared to a value of 54 cm2 C−1 obtained for the WO3–PB (PMMA) device. Similar enhancements in electrochromic coloring efficiency, reflectance contrast, and faster switching kinetics were obtained for the PEDOT–PB (MMA) device. The strategy of introducing an electrolyte to the electrochromic device in a liquid state and then subjecting the same to gradual polymerization allows greater accessibility of the electrolyte ions to the active sites on the electrochromic electrodes and superior interfacial contact. As a consequence, larger optical contrast and faster kinetics are achieved in the MMA based devices. While PEDOT films were amorphous, PB films were semi-crystalline but only in the case of WO3; the hexagonal structure of WO3, equipped with three/four/six-coordinated voids was found to affect bleaching kinetics favorably. The performance of PMMA based electrolyte is limited by high resistance at the electrode–electrolyte interface, and a smaller number of ions available for oxidation and reduction. Large area (∼10 cm × 4 cm) devices were also fabricated using this simple wet chemistry method and their ability to color uniformly without any pinholes was demonstrated.

High-performance, mechanically compliant silica-based ionogels for electrical energy storage applications

The development of an ionic liquid-rich (∼94% by mass), mechanically compliant, silica-supported ionogel (ionic liquid-based gel electrolyte) is described. This new form of ionogel was created using a straightforward sol–gel process with a novel formulation of reactants, resulting in a versatile, stable, and high-performance solid electrolyte. The mechanically compliant ionogels described herein show both capacitance and ionic conductivity values at room temperature nearly equivalent to those of the neat ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EMI TFSI), in addition to exhibiting a wide window of electrochemical stability. Compliant ionogels (elastic modulus of ∼5 kPa) show markedly different mechanical character than previously reported silica ionogels, which are mechanically brittle and exhibit lower ionic conductivity and double-layer capacitance. The silica microstructure is shown to be tunable by simple alterations of the reagent formulation. Compliant ionogels may be suitable for in situ fabrication of flexible, thin-film energy storage devices such as supercapacitors.

Ion transport properties of ionic liquid based gel electrolytes

Ion transport properties of two types of gel electrolytes based on the same ionic liquid (IL) 2,3-dimethyl-1-hexyl imidazolium bis (trifluoromethanesulfonyl) imide (DMHxImTFSI), namely polymer-in-IL, containing DMHxImTFSI and polyethylene oxide (PEO) and polymer gel electrolytes containing DMHxImTFSI, PEO and propylene carbonate (PC) have been studied over a wide temperature range. The ionic conductivity of polymer-in-IL gels is of the order of 10 −3 S cm −1 at 25 °C, which increases to 10 −2 S cm −1 at 127 °C and these gels are thermally stable up to 400 °C. Polymer gel electrolytes containing PC show relatively higher ionic conductivity than polymer-in-IL gels but have lower thermal stability. Line narrowing observed in the variation of line width of 1H and 19F NMR lines with temperature shows the simultaneous presence of high and low conducting phases in polymer-in-IL gels whereas high conducting amorphous phase is mainly present in polymer gel electrolytes containing PC. The onset of long range translational motion in these gel electrolytes has been observed to take place at the glass transition ( T g) and melting ( T m) temperature and is closely related to the ionic conductivity of the gel electrolytes. The range of temperature over which the gel electrolytes possess higher ionic conductivity has also been identified. The polymer has been observed to play an active role in polymer gel electrolytes whereas it mainly acts as a stiffener in polymer-in-IL gels. The polymer gel electrolytes containing PC can be used in practical devices at temperatures below 100 °C whereas polymer-in-IL gels can be used up to 400 °C.

Gelation of Ionic Liquid-Based Electrolyte with Ordered Mesoporous Silica Particles for Quasi-Solid-State Dye-Sensitized Solar Cells

Ordered Mesoporous Silica with Uniform Pore Size Was Prepared by Using Pluronic P123 as the Structure-Directing Agent. their Characteristics Were Analysized by TEM and a N2Adsorption System. Ionic Liquid-Based Gel Electrolyte Was Fabricated by Using Ordered Mesoporous Silica as the Framework Materials to Solidify Ionic Liquid Electrolyte. the Diffusion Coefficient of I3-in Gel Electrolyte Is Higher than that in Ionic Liquid Electrolyte due to the Formation of Favorable Channel for I3-Diffusion. the Optimized Overall Conversion Efficiency of Dye-Sensitized Solar Cells with Ionic Liquid-Based Gel Electrolyte Was 5.22% under Irradiation of 60 MW Cm-2.

A Dual Electrochrome of Poly‐(3,4‐Ethylenedioxythiophene) Doped by N,N′‐Bis(3‐sulfonatopropyl)‐4‐4′‐bipyridinium—Redox Chemistry and Electrochromism in Flexible Devices

An electrochromic zwitterionic viologen, N,N'-bis(3-sulfonatopropyl)-4-4'-bipyridinium, has been used for the first time for doping poly (3,4-ethylenedioxythiopene) (PEDOT) films during electropolymerization. Slow and fast diffusional rates for the monomer at deposition potentials of +1.2 and +1.8 V, respectively yielded the viologen-doped PEDOT films with granular morphology and with dendrite-like shapes. The dual electrochrome formed at +1.8 V, showed enhanced coloration efficiency, larger electrochemical charge storage capacity, and superior redox activity in comparison to its analogue grown at +1.2 V, thus demonstrating the role of dendritic shapes in amplifying electrochromism. Flexible electrochromic devices fabricated with the viologen-doped PEDOT film grown at +1.8 V and Prussian blue with an ionic liquid-based gel electrolyte film showed reversible coloration between pale and dark purple with maximum coloration efficiency of 187 cm2C(-1) at lambda=693 nm. The diffusional impedance parameters and switching kinetics of the device showed the suitability of this dual electrochrome formed as a single layer for practical electrochromic cells.

Electrochemistry of poly(3,4-ethylenedioxythiophene)-polyaniline/Prussian blue electrochromic devices containing an ionic liquid based gel electrolyte film

Electrochromic devices based on poly(3,4-ethylenedioxythiophene) (PEDOT) as the cathodic coloring electrode and polyaniline (PANI) or Prussian blue (PB) as the counter electrode containing a highly conductive, self-supporting, distensible and transparent polymer-gel electrolyte film encapsulating an ionic liquid, 1-butyl-1-methylpyrrolidiniumbis-(trifluoromethylsulfonyl)imide, have been fabricated. Polarization, charge transfer and diffusion processes control the electrochemistry of the functional electrodes during coloration and bleaching and these phenomena differ when PEDOT and PANI/PB were employed alternately as working electrodes. While the electrochemical impedance response shows good similitude for PEDOT and PANI electrodes, the responses of PEDOT and PB were significantly different in the PEDOT-PB device, especially during reduction of PB, wherein the overall amplitude of the impedance response is enormous. Large values of the coloration efficiency maxima of 281 cm2 C(-1) (lambda = 583 nm) and 274 cm2 C(-1) (lambda = 602 nm), achieved at -1.0 and -1.5 V for the PEDOT PANI and PEDOT-PB devices have been correlated to the particularly low magnitude of charge transfer resistance and high polarization capacitance operative at the PEDOT ionic liquid based electrolyte interface at these dc potentials, thus allowing facile ion-transport and consequently resulting in enhanced absorption modulation. Moderately fast switching kinetics and the ability of these devices to sustain about 2500 cycles of clear-to-dark and dark-to-clear without incurring major losses in the optical contrast, along with the ease of construction of these cells in terms of high scalability and reproducibility of the synthetic procedure for fabrication of the electrochromic films and the ionic liquid based gel electrolyte film, are indicators of the promise these devices hold for practical applications like electrochromic windows and displays.

The Effect of the Ethylene Carbonate Addition on the Properties of Ionic Liquid-based Gel Electrolyte

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Ionic Liquid Based Gel Electrolyte Compositions for Dye Sensitized Solar Cells

ABSTRACTKonarka Technologies has developed efficient electrolyte compositions based on nonvolatile ionic liquids. The electrolyte compositions were subsequently gelled using a metal ion complexation technique, without compromising the photovoltaic performance of the dye sensitized solar cells (DSSCs). The photovoltaic performance of the gel electrolyte incorporated DSSCs is quite stable for extended period of time even in the absence of sealing. Detailed results on performance and stability of the gel electrolyte incorporated DSSCs are presented.