Ionic Gel Electrolyte Research Articles

Carbon Nanotube Wires Sheathed by Aramid Nanofibers

Coaxial fibers are the key elements in many optical, electrical, and biomedical applications. Recent success in materials synthesis has provided versatile choices for the core part, but the search of high‐performance sheath materials remains much less productive. These surface coatings are however as important as the core for their role as protection layers and interaction medium with the externals, thereby critically affecting the real performance of coaxial fibers. Here it is shown that aramid nanofibers (ANFs) with exceptional environmental stability and mechanical properties can be advanced coating materials for both wet‐ and dry‐spun carbon nanotube (CNT) wires. Co‐wet‐spinning ANFs with CNT aqueous dispersion can produce coaxial fibers with a compact sheath comprised of aligned ANFs, showing much enhanced mechanical properties by transferring stress to the sheath without sacrificing the conductivity. On the other hand, an immersion‐precipitation process is used to prepare a porous sheath made from randomly distributed nanofibers on dry‐spun CNT wires, which can be combined with ionic conductive gel electrolyte as a strong packaging layer for flexible solid‐state supercapacitors. The excellent intrinsic characteristics as well as variable ways of structural organizations make ANF‐based coatings an attractive tool for the design of multifunctional high‐performance hybrid materials.

High performance photolithographically-patterned polymer thin-film transistors gated with an ionic liquid/poly(ionic liquid) blend ion gel

We demonstrate the fabrication of polymer thin-film transistors gated with an ion gel electrolyte made of the blend of an ionic liquid and a polymerised ionic liquid. The ion gel exhibits a high stability and ionic conductivity, combined with facile processing by simple drop-casting from solution. In order to avoid parasitic effects such as high hysteresis, high off-currents, and slow switching, a fluorinated photoresist is employed in order to enable high-resolution orthogonal patterning of the polymer semiconductor over an area that precisely defines the transistor channel. The resulting devices exhibit excellent characteristics, with an on/off ratio of 106, low hysteresis, and a very large transconductance of 3 mS. We show that this high transconductance value is mostly the result of ions penetrating the polymer film and doping the entire volume of the semiconductor, yielding an effective capacitance per unit area of about 200 μF cm−2, one order of magnitude higher than the double layer capacitance of the ion gel. This results in channel currents larger than 1 mA at an applied gate bias of only –1 V. We also investigate the dynamic performance of the devices and obtain a switching time of 20 ms, which is mostly limited by the overlap capacitance between the ion gel and the source and drain contacts.

Low-Voltage 2D Material Field-Effect Transistors Enabled by Ion Gel Capacitive Coupling

Capacitive coupling between an overlying ion gel electrolyte and an underlying oxide thin film is utilized to substantially suppress the operating voltage of field-effect transistors (FETs) based on two-dimensional (2D) transition metal dichalcogenides and black phosphorus. The coupling of the layers is achieved following device fabrication by laminating an ion gel layer over an oxide-gated 2D FET through solution-casting methods. While the original pristine 2D FET requires tens of volts for gating through the oxide layer, the laminated ion gel layer reduces the operating voltage to below 4 V even when the same underlying substrate is used as the back gate electrode. Moreover, this capacitive coupling approach allows low-voltage operation without compromising the off-current level, which often occurs when ion gel electrolytes are directly employed as the gate dielectric material. This approach can likely be generalized to a wide variety of thin-film FETs as a postfabrication method for reducing operating voltages and power consumption.

Hybrid ionogels derived from polycationic polysilsesquioxanes for lithium ion batteries

A multifunctional crosslinkable and ionic-group functionalized ladder-like polysilsesquioxane was synthesized and utilized for the fabrication of hybrid ionogels for lithium ion batteries. The ionic-group functionalized ladder-like polysilsesquioxane combined the synergistic effects of hybrid materials in improving the thermal stability of conventional battery electrolytes, whilst maintain facile solution processability and chemically crosslinkable function in ionic conducting ionic liquid electrolyte media. Fabricated iongel electrolytes exhibiting exceptional thermal stability, mechanical properties, high ionic conductivity, and electrochemical stability. Lithium ion batteries fabricated with the hybrid ionic ladder-like polysilsesquioxane ionogels exhibited initial discharge capacities on par with neat liquid electrolytes, good rate performance, as well as stable cyclability and excellent Coulombic efficiency.

Monolithic Flexible Supercapacitors Integrated into Single Sheets of Paper and Membrane via Vapor Printing.

A novel approach to fabricate supercapacitors (SCs) via vapor printing, specifically oxidative chemical vapor deposition (oCVD), is demonstrated. Compared to stacking multiple layers into a SC, this method enables the monolithic integration of all components into a single-sheet substrate, minimizing the inactive materials and eliminating the possibility of multilayer delamination. Electrodes comprised of pseudocapacitive material, poly(3,4-ethylenedioxythiophene) (PEDOT), are deposited into both sides of a sheet of flexible porous substrate. The film deposition and patterning are achieved in a single step. The oCVD PEDOT penetrates partially into the porous substrate from both surfaces, while leaving the interior of the substrate serving as a separator. Near the surface, the PEDOT coating conforms to the substrate's structure without blocking the pores, resembling the substrate's intrinsic morphology with high surface area. The porously structured PEDOT coating, paired with in situ ion gel electrolyte synthesis, gives enhanced electrode-electrolyte interfaces. The monolithic device demonstrates high volumetric capacitance (11.3 F cm-3 ), energy density (2.98 mWh cm-3 ), and power density (0.42 W cm-3 ). These outstanding performance metrics are attributed to the large loading of active materials, minimization of inactive materials, and good electrode-electrolyte interfaces. SC arrays can be printed on a single substrate without the use of wire interconnects.

A transparent solid-state ion gel for supercapacitor device applications

A feasibility study of the synthesis of gel polymer electrolytes based in methyl methacrylate (MMA) and 1-vinyl-2-pyrrolidone (VP) using [HEMIm][BF4] as common ionic liquid has been done. A novel PVP/[HEMIm][BF4] solid-state and self-standing ion gel electrolyte has been successfully prepared. The thermal degradation of PVP/[HEMIm][BF4] ion gel occurs in two steps with the first one at above 200 °C and the main one over 390 °C. This solid-state ion gel is transparent, showing an optical transmittance with a maximum value of 90% in the visible wavelength region from 370 to 770 nm. The synthesized PVP/[HEMIm][BF4] solid-state ion gel exhibits an electrochemical stability window of ca. 5.0 V and an acceptable ionic conductivity of σ = 5.7 10−3 S cm−1 at room temperature. A symmetrical pseudocapacitive supercapacitor has been assembled and characterized using this PVP/[HEMIm][BF4] solid-state ion gel—glass/ITO/PEDOT/PVP/[HEMIm][BF4]/PEDOT/ITO/glass. It is found that the supercapacitor shows a typical areal specific capacitance of 3.1 mF cm−2, a maximum energy density of 2.5 μWh cm−2, and an areal specific power density of ca. 1 mW cm−2.

1-Ethyl-3-methylimidazolium tetrafluoroborate-doped high ionic conductivity gel electrolytes with reduced anodic reaction potentials for electrochromic devices

The electrolyte plays an important role in an electrochromic device (ECD), and an ideal electrolyte can greatly improve the electrochromic performance of the device. Here, we report the preparation of a 1-Ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4)-doped Poly(methyl methacrylate) (PMMA)-based gel electrolyte for electrochromic applications. By the doping of the [Emim]BF4, the ionic conductivity of the gel electrolyte is improved (2.9×10−3S/cm at room temperature and 10−2S/cm at 40°C). Most importantly, the addition of the [Emim]BF4 could reduce the anodic reaction potentials in an ECD, which could enable ECD bleaching at smaller applied voltages and avoid the degradation of optical modulation induced by ion-trapping in tungsten oxide (WO3) films. This novel electrolyte provides a promising platform for low anodic reaction potential electrochromic devices.

Quasi-Solid-State Dye-Sensitized Solar Cell with Ionic Gel Electrolytes by Semifluorinated Alkoxyl Benzene Derivatives

Low molecular-mass organic compounds 1 and 2 having 2-(perfluoroalkyl)ethyl groups at both terminal positions were prepared and their gelation abilities were explored. Compounds 1 and 2 without hydrogen bonding group can gelatinize various organic solvents and/or ionic liquids at low concentration. Compound 1 can gelatinize toluene, while compound 2 dissolve in toluene. Compounds 1 and 2 gelatinize electrolyte showing effective gelation properties. The firmed supramolecular gels are physical gels with thermally reversible sol-gel phase transition. The difference of ionic conductivity between liquid state and gel state were analyzed.

ポリベタイン型イオンゲルの合成と電解質としての評価

オリゴエーテルモノマー，双性イオンモノマーおよびイオン液体/リチウム塩複合体を所定量混合し，in situ重合によりポリベタイン型イオンゲルを合成した．いずれのイオンゲルも－70°C付近にガラス転移温度(Tg)のみを示した．イオンゲルのイオン伝導度はリチウム塩濃度や双性イオンユニットの含量に依存せず，室温において同等の値を示した．これらイオンゲルの酸化安定性およびリチウムの酸化還元に関するクーロン効率は双性イオンユニットの含量の増加に伴い向上した．

Reduced graphene oxide paper as bimorphic electrical actuators

Reduced graphene oxide (rGO) papers prepared by simple self-assembly process were used as electrode material for the fabrication of bimorphic electrical actuators. Initially, the structural studies of the rGO paper confirmed the formation of graphitic structure. The ionic gel electrolyte was prepared separately and used to couple the two rGO paper electrodes. This forms the tri-layered structure as an actuator, the displacement was measured by varying the applied potential with respect to time. The actuation properties were extended for both photon as well as electronic conducting gel electrolyte. The experimental results suggest that the flexible rGO paper can be used for electronic actuators.

Molecular interactions in high conductive gel electrolytes based on low molecular weight gelator

Organic ionic gel (OIG) electrolytes, also known as gel electrolytes or ionogels are one example of modern functional materials with the potential to use in wide range of electrochemical applications. The functionality of OIGs arises from the thermally reversible solidification of electrolytes or ionic liquids and their superior ionic conductivity. To understand and to predict the properties of these systems it is important to get the knowledge about the interactions on molecular level between the solid gelator matrix and the electrolyte solution. This paper reports the spectroscopic studies (FT-IR, UV–Vis and Raman) of the gel electrolyte based on low molecular weight gelator methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside and solution of quaternary ammonium salt, tetramethylammonium bromide. The solidification process was based on sol-gel technique. Below characteristic temperature, defined as gel to sol phase transition temperature, Tgs, the samples were solid-like and showed high conductivity values of the same order as observed for pure liquid electrolytes. The investigations were performed for a OIGs in a wide range of molar concentrations of the electrolyte solution.

Quasi-Solid-State Dye-Sensitized Solar Cell with Ionic Gel Electrolytes By Semifluorinated Alkoxy Benzene Derivative

Quasi-solid-state dye-sensitized solar cells (QS-DSSCs) have rapidly become an important research orientation in electronic vehicles. Especially, ionic liquid gel electrolytes (ILGEs) solidified by low molecular mass organogelators (LMOGs) can effectively possess higher ionic conductivity and good pore filling.1 Based on the advantage of ILGEs, we present here a kind of LMOGs (compounds 1(n)) by semifluorinated benzene derivatives. ILGEs formed by compounds 1(n) with different ionic liquids can divide two parts. One is with the representative [BMIM] posion-based ionic liquids (ILs), such as [BMIM] [I], [BMIM] [BF4], [BMIM] [FSA] and [BMIM] [TFSA]. Another one is with the representative [TFSA] anion-based ILs, such as [DEME] [TFSA], [EMIM] [TFSA], [TMPA] [TFSA], [AAIM] [TFSA] and [P13] [TFSA]. The minimum gelation concentrations in weight percent were determined at concentrations ranging from 5% to 1% in a heating-cooling cycle by the “stable to inversion in a test tube” method. The thermal properties of ILGEs which exactly is the effect of the concentration on the gel-sol phase transition temperatures (T gel) upon heating were examined. The ionic conductivity (σ) of ILGEs which is an important property for ILGEs was also examined. Compared with the data of ionic conductivities which has been reported in literature, it was found that the ionic conductivities in gel state were similar with ionic conductivities in liquid state. The conductivities of ILGEs with different concentrations of LMOGs were also analyzed. The diffusion of redox couple (I3 - and I-) ions in the ILGEs is an important factor for DSSCs property.2 In order to analyze the behavior of in I3 - and I- the ILGEs, linear sweep voltammetry studies were performed at a scan rate of 1.0 mVs-1 at room temperature. The performance of [BMIM] [I] was different with others. It maybe that ionic liquid of [BMIM] [I] contains anion of I- by itself. Reference 1. (a) Wang, P.; Zakeeruddin, S. M.; Comte, P.; Exnar, I.; Grätzel, M. Gelation of ionic liquid-based electrolytes with silica nanoparticles for quasi-solid-state dye-sensitized solar cells. Journal of the American Chemical Society 2003, 125 (5), 1166-1167; (b) Tao, L.; Huo, Z.; Ding, Y.; Li, Y.; Dai, S.; Wang, L.; Zhu, J.; Pan, X.; Zhang, B.; Yao, J. High-efficiency and stable quasi-solid-state dye-sensitized solar cell based on low molecular mass organogelator electrolyte. Journal of Materials Chemistry A 2015, 3 (5), 2344-2352. 2. Yoon, J.; ki Kang, D.; Won, J.; Park, J.-Y.; Kang, Y. S. Dye-sensitized solar cells using ion-gel electrolytes for long-term stability. Journal of Power Sources 2012, 201, 395-401.

Encapsulated, High-Performance, Stretchable Array of Stacked Planar Micro-Supercapacitors as Waterproof Wearable Energy Storage Devices.

We report the fabrication of an encapsulated, high-performance, stretchable array of stacked planar micro-supercapacitors (MSCs) as a wearable energy storage device for waterproof applications. A pair of planar all-solid-state MSCs with spray-coated multiwalled carbon nanotube electrodes and a drop-cast UV-patternable ion-gel electrolyte was fabricated on a polyethylene terephthalate film using serial connection to increase the operation voltage of the MSC. Additionally, multiple MSCs could be vertically stacked with parallel connections to increase both the total capacitance and the areal capacitance owing to the use of a solid-state patterned electrolyte. The overall device of five parallel-connected stacked MSCs, a microlight-emitting diode (μ-LED), and a switch was encapsulated in thin Ecoflex film so that the capacitance remained at 82% of its initial value even after 4 d in water; the μ-LED was lit without noticeable decrease in brightness under deformation including bending and stretching. Furthermore, an Ecoflex encapsulated oximeter wound around a finger was operated using the stored energy of the MSC array attached to the hand (even in water) to give information on arterial pulse rate and oxygen saturation in the blood. This study suggests potential applications of our encapsulated MSC array in wearable energy storage devices especially in water.

Ionic gel electrolytes composite with SiO2 nanoparticles for quasi-solid-state dye-sensitized solar cells

Composite ionic gel electrolytes were facilely prepared by mixing ionic gel electrolytes with SiO2 nanoparticles. The dye-sensitized solar cells (DSSCs) assembled with the composite ionic gel electrolytes exhibit the higher photovoltaic performance and better durability compared to the original DSSCs based on pure ionic gel electrolytes. In particular, the DSSC assembled with the electrolytes containing 0.15 g of SiO2 shows superior J SC (14.4 mA cm−2), V OC (0.67 V), fill factor (0.69) and power conversion efficiency (6.71 %) (measured at AM 1.5, light intensity of 100 mW/cm2). The electrochemical impedance spectra, SEM and conductivity were used to characterize the composite ionic gel electrolytes.

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.

Ionic Conductivity and Thermal Properties of a Supramolecular Ionogel Made from a Sugar-Based Low Molecular Weight Gelator and a Quaternary Ammonium Salt Electrolyte Solution

Smart, functional, or intelligent materials are no longer just theoretical systems; they now have applications in different fields of everyday life. One example of this class of materials with the potential for use in a wide range of applications is organic ionic gel (OIG) electrolytes, also known as gel electrolytes or ionogels. The functionality of OIGs arises from the thermally reversible solidification of electrolytes or ionic liquids and their superior conductivity properties. The performance of a series of ionogel samples made from a low molecular weight organic gelator (LMWG) and a quaternary ammonium salt electrolyte solution was studied by means of conductometry, thermal analysis, and microscopic observation. The solidification process was based on the sol-gel technique with controlled gelation temperature. The use of thermal scanning conductometry (TSC) allowed for in situ studies of the conductivity properties, reversibility, and reproducibility of the ionogel system in gel-sol-gel-sol phase transition cycles. As a result, the best chemical composition of the recoverable OIG system based on methyl-4,6-O-(p-nitrobenzylidene)-α-D-glucopyranoside (1) and tetramethylammonium bromide (TMABr) was determined in terms of its thermal and conductivity properties.

Mediating Gel Formation from Structurally Controlled Poly(ionic liquids): Towards Ionic Gel Electrolytes for Energy Storage

Most sustainable energy sources (solar, hydropowered, geopowered, windpowered) rely on the production of electrical energy. In the last decade, Lithium ion based batteries have emerged as interesting candidates as high-density energy storage devices, enabling the developments of electrical vehicles of constantly growing autonomies. The synthesis of polymer electrolytes and the study of their electrochemical properties is currently a very active topic. Poly(ionic liquids) (PILs), in particular, constitute an increasingly sought-after category of materials, as they are expected to replace flammable, leakage-prone organic solvent electrolytes in future energy storage devices.[1,2] In this communication, we will present a novel synthetic methodology, which provides an easy access to a broad range of PILs from a common monomeric precursor (figure 1). Owing to this straightforward conceptual approach, it is possible to precisely control the structure of the polymeric materials. We will show how the introduction of an anionic functional group on the ATRP initiator is enough to mediate gel formation at low concentrations through electrostatic interactions (Figure 2).[3,4] We will then demonstrate that the incorporation of different additives along the polymer backbone helps optimizing ionogel properties in different electrolytic solvents to form gel electrolyte. Finally, we will illustrate the potential of the resulting gels as quasi-solid materials for energy storage applications through the study of different parameters: its rheological behaviour, electrochemical stability, diffusion and ionic conductivity properties. [1] Yoshizawa, M.; Ogihara, W.; Ohno, H. Polym. Adv. Technol. 2002, 13, 589-594. [2] Wang, P.; Zakeeruddin, S. M.; Moser, J. E.; Nazeeruddin, M. K.; Sekiguchi, T.; Gratzel, M. Nat Mater 2003, 2, 402-407. [3] Appukuttan, V. K.; Dupont, A.; Denis-Quanquin, S.; Andraud, C.; Monnereau, C. Polym. Chem. 2012, 3, 2723-2726. [4] Srour, H.; Ratel, O.; Leocmach, M.; Adams, E. A.; Denis-Quanquin, S.; Appukuttan, V.; Taberlet, N.; Manneville, S.; Majesté, J.-C.; Carrot, C.; Andraud, C.; Monnereau, C. Macromol. Rapid Commun. 2014, DOI: 10.1002/marc.201400478. Figure 1

Effect of alkyl chain length of imidazolium cations on the electron transport and recombination kinetics in ionic gel electrolytes based quasi-solid-state dye-sensitized solar cells

A series of stable quasi-solid-state dye-sensitized solar cells (QS-DSSCs) are prepared by the 12-hydroxystearicacid as low molecular mass organogelator (LMOG) to gelate the ionic liquid with different alkyl chain lengths (3, 4, and 7). The influence of alkyl chain length of imidazolium cations (Im+) on the kinetic processes of electron transport and recombination are investigated by Electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent spectroscopy/intensity-modulated photovoltage spectroscopy (IMPS/IMVS). It is found that the ionic gel electrolytes (IGEs) with different alkyl chain lengths of Im+ can influence the competitive adsorption effects of imidazolium cations (Im+) and Li+, and further affect the charge diffusion, the electron recombination/transport processes, the shift of TiO2 conduction band edge and surface states distribution. The IGE with longer alkyl chain length of Im+ can prolong the electron recombination lifetime, promote the incidental photon-to-electron conversion efficiency (IPCE) and the short circuit photocurrent density (Jsc). An excellent QS-DSSC based on the IGE with the longer alkyl chain of Im+ gives the highest photoelectric conversion efficiency. Moreover, all the QS-DSSCs based on IGEs exhibit excellent durability without losing their photovoltaic performances during the accelerated thermal and light–soaking test. These results are very important to the researches on the electrochemical mechanism and application of QS-DSSCs based on IGEs.

Nanoplatelets bridging a nanotrench: a new architecture for photodetectors with increased sensitivity.

Interparticle charge hopping severely limits the integration of colloidal nanocrystals films for optoelectronic device applications. We propose here to overcome this problem by using high aspect ratio interconnects made of wide electrodes separated by a few tens of namometers, a distance matching the size of a single nanoplatelet. The semiconducting CdSe/CdS nanoplatelet coupling with such electrodes allows an efficient electron-hole pair dissociation despite the large binding energy of the exciton, resulting in optimal photoconductance responsivity. We report the highest responsivity obtained so far for CdSe colloidal material with values reaching kA·W(-1), corresponding to eight decades of enhancement compared to usual micrometer-scaled architectures. In addition, a decrease of 1 order of magnitude of the current noise is observed, revealing the reduced influence of the surface traps on transport. The nanotrench geometry provides top access to ion gel electrolyte gating, allowing for a photoresponsive transistor with 10(4) on/off ratio. A simple analytical model reproduces the device behavior and underlines the key parameters related to its performance.

Stable quasi-solid-state dye-sensitized solar cell using ionic gel electrolyte with low molecular mass organogelator

Long-term stability is essential for the application and commercialization of dye-sensitized solar cells (DSCs). A quasi-solid-state DSC (QS-DSC) with excellent long-term stability is fabricated using ionic gel electrolyte (IGE) with N,N′-methylenebisdodecanamide as low molecular mass organogelator (LMOG). The gel to solution transition temperature (Tgel) of this IGE is 127 °C, well above the working temperature of the device, which contributes to the thermal properties of the IGE and the device. The electrochemical properties of the IGE and the kinetic processes of electron transport and recombination of the QS-DSC are investigated by means of electrochemical impedance spectroscopy (EIS) and controlled intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). Due to the obstructed diffusion of redox species caused by the network of IGE, the electron recombination at the TiO2 photoelectrode/electrolyte interface in the QS-DSC is accelerated. More importantly, compared with the ionic liquid electrolyte (ILE) based DSC, the QS-DSC based on the IGE exhibits excellent thermal and light-soaking stabilities during the accelerated aging tests for 1000 h. Especially, there is almost no degradation in the short-circuit current density (Jsc) in the IGE based QS-DSC, while the Jsc of the ILE based DSC decreased to 85–94% of their initial values.