Ionic Gel Electrolyte Research Articles

Transparent Electrode‐Free Light‐Emitting Devices Exploiting Ion Transport‐Controlled Electrochemiluminescence

AbstractTransparent electrode‐free light‐emitting devices are presented that exploit electrochemiluminescence (ECL). These devices feature two side‐by‐side noble metal electrodes connected by an ECL active layer. The significance of bulk ion‐transport characteristics is investigated within the ECL active layer in producing uniform planar emission from the device. These characteristics can be enhanced by simply increasing the ECL active layer thickness or adding an ion gel electrolyte layer on top of the ECL active layer. The use of only electrochemically stable noble metal electrodes results in an operational lifetime exceeding 10 h, which is the longest lifetime reported for ECL‐based light‐emitting devices to date. The device structure based on ECL does not require transparent electrodes, allowing for increased flexibility when designing devices for future light‐emitting device applications.

Highly Stretchable Supercapacitor‐Type Multifunctional Self‐Powered Porous Electronic Skins

AbstractThe development of highly stretchable self‐powered electronic skins with a broad detection range is urgently needed but remains a great challenge. Herein, unprecedented highly stretchable, broad‐range‐response, supercapacitor‐type, one‐body, and self‐powered electronic skins are developed by assembling porous polyurethane/polypyrrole electrode, polyacrylic acid/polyacrylamide ionic gel electrolyte, and porous polyurethane/MXene electrode. The folded porous structure of the electrodes significantly enhances the stretchability, while the modulus‐gradient multilayer structure of the device effectively broadens the pressure detection range. The electronic skins combine self‐powered dynamic/static pressure sensing, ultrabroad detection range (20 Pa–3.5 MPa), ultrahigh stretchability up to 387%, excellent compression stability (5000 cycles under 195 kPa), and good stretching stability (500 cycles under 200% tensile strain). They have the capability of monitoring human body motions, physiological signals, and high pressures from motorcycle tires, as well as tactile sensing of robotic grippers. In addition, they can be applied for highly stretchable thermal management and electromagnetic shielding devices. This work provides a new strategy for the development of highly stretchable, broad‐range‐response, and multifunctional self‐powered wearable electronics and sensors.

In-Sensor Organic Electrochemical Transistor for the Multimode Neuromorphic Olfactory System.

The olfactory system is one of the six basic sensory nervous systems. Developing artificial olfactory systems is challenging due to the complexity of chemical information decoding and memory. Conventional chemical sensors can convert chemical signals into electric signals to decode gas information but they lack memory functions. Additional storage and processing units would significantly increase the complexity and power consumption of the devices, especially for portable and wearable devices. Here, an olfactory-inspired in-sensor organic electrochemical transistor (OI-OECT) is proposed, with the integrated functions of chemical information decoding, tunable memory level, and selectivity of vapor sensing. The ion-gel electrolyte endows the OI-OECT with the function of tunable memory levels and a low operating voltage. Typical synaptic behaviors, including inhibitory postsynaptic current and paired-pulse facilitations, are successfully achieved. Importantly, the gas memory level can be effectively modulated by the gate voltages (0 and -1 V), which realized the transformation of volatile and nonvolatile memory. Furthermore, benefiting from the recognition of multiple gases and ability to detect cumulative damage caused by gases, the OI-OECT is demonstrated for early warning system targeting leakage detection of two gases (NH3 and H2S). This work achieves the integrated functions of chemical gas information decode, tunable gas memory level, and selectivity of gas in a single device, which provides a promising pathway for the development of future artificial olfactory systems.

In Situ Polymerized Zwitterionic Copolymer Ionic Gel Electrolytes with High Performance for Lithium-Ion Batteries.

Gel electrolytes are a promising research direction due to their high safety. However, its poor room temperature conductivity along with complex preparation process hinder its practical application. In this article, a type of zwitterionic gel electrolyte is prepared by in situ polymerization. The introduction of charged but nonmigrating zwitterionic copolymer in the polymer chain is beneficial to the dissociation of the lithium salt, improving the ion transport of the electrolyte on this account. At room temperature, the conductivity of lithium ion reaches 9.1 × 10-4 S cm-1, which contributes to achieve excellent electrochemical performance at high rates. The assembled Li|LiFePO4 cell also shows a capacity retention rate of 90.5% after 150 cycles at 0.5 C at room temperature as well as remarkable cycle stability at 1 C. These offer a novel tactic for the efficient and safe commercial application of lithium-ion batteries.

Ethanol Vapor‐Induced Synthesis of Robust, High‐Efficiency Zinc Ion Gel Electrolytes for Flexible Zn‐Ion Batteries

The evolution of flexible Zn‐ion batteries (FZIBs) significantly hinges on the development of gel electrolytes, characterized by their mechanical properties, ionic conductivity, and environmentally friendly production processes. The prevailing challenge in this domain has been devising a gel electrolyte that encapsulates all these critical attributes effectively for practical application. This study presents a novel zinc ion gel (Zn‐gel) electrolyte developed for FZIBs, synthesized via ethanol vapor‐induced assembly of cellulose molecules. This innovative process fosters significant hydrogen bonding and ion‐complexation with Zn2+ ions, resulting in a gel with exceptional mechanical strength (0.88 MPa), high ion transference (over 0.7), and impressive ionic conductivity (8.39 mS cm−1). The Zn‐gel enables a FZIB to achieve a reversible capacity of 207.3 mAh g−1 and over 93% Coulombic efficiency after 500 cycles, devoid of liquid electrolyte. Highlighting a promising route for high‐performance, eco‐friendly gel electrolytes, this research advances flexible electronics and portable device applications, demonstrating the profound potential of bio‐based polymers in enhancing energy storage technology.

High toughness antifreeze conductive double network zwitterionic gel electrolyte for flexible supercapacitors

AbstractFlexible wearable supercapacitors based on hydrogel electrolyte are considered as flexible energy storage device with great potential. However, polymer gel electrolytes contain a large number of water molecules, which can easily freeze at sub‐zero temperatures, thus severely inhibiting ion transport. The ionic conductivity, cyclic stability and mechanical properties of gel electrolytes decrease at low temperatures (below −25°C), which seriously hinders the application of flexible wearable supercapacitors. In order to improve the mechanical properties and ensure the excellent ionic conductivity of the electrolyte, a freezing‐resistant gel electrolyte constructed by supramolecular self‐assembly, which has a wide temperature range from 25 to −80°C, stable ionic conductivity and ultra‐high mechanical strength. Low‐temperature‐resistant gel electrolytes, called flexible supercapacitor‐SBMA‐co‐PVA‐AA/CaCl2 (FSAPC), have been designed and prepared by molecular‐scale supramolecular self‐assembly of rigid [2‐(methacryloyloxy)ethyl]dimethyl(3‐sulfopropyl) polymer chains and flexible poly(vinyl alcohol) polymer chains, and the test results showed that the gel electrolyte ‐SBMA‐co‐PVA‐AA/CaCl2 (PSAPC) has excellent conductivity of 34.07 mS cm−1 at 25°C, the flexible supercapacitor has a specific capacity of 8.57 Wh kg−1, and the capacity retention rate is 91.2% even after 5000 cycles at −25°C, excellent conductivity at −25°C for 31.88 mS cm−1 and at −80°C for 35.34 mS cm−1. The potential applications of the amphiphilic ionic gel electrolyte in the industrial development of low‐temperature resistant supercapacitors are noteworthy.

Self‐powered sensor based on compressible ionic gel electrolyte for simultaneous determination of temperature and pressure

AbstractThe simultaneous detection of multiple stimuli, such as pressure and temperature, has long been a persistent challenge for developing electronic skin (e‐skin) to emulate the functionality of human skin. Meanwhile, the demand for integrated power supply units is an additional pressing concern to achieve its lightweightness and flexibility. Herein, we propose a self‐powered dual temperature–pressure (SPDM) sensor, which utilizes a compressible ionic gel electrolyte driven by the potential difference between MXene and Al electrodes. The SPDM sensor exhibits a rapid and timely response to changes in pressure‐induced deformation, while exhibiting a slow and hysteretic response to temperature variations. These distinct response characteristics enable the differentiation of current signals generated by different stimuli through machine learning, resulting in an impressive accuracy rate of 99.1%. Furthermore, the developed SPDM sensor exhibits a wide pressure detection range of 0–800 kPa and a broad temperature detection range of 5–75°C, encompassing the environmental conditions encountered in daily human life. The dual‐mode coupled strategy by machine learning provides an effective approach for temperature and pressure detection and discrimination, showcasing its potential applications in wearable electronics, intelligent robots, human–machine interactions, and so on.

Experimental and computational analysis of the structure-activity relationship of ionic gel electrolytes based on bistrifluoromethanesulfonimide salts for supercapacitors

Ionic gel (IG) electrolytes are emerging as promising components for the development of next-generation supercapacitors (SCs), offering benefits in terms of safety, cost-effectiveness, and flexibility. The ionic conductivity, stability, and mechanical properties of the gel electrolyte are relevant factors to be considered and the key to improving the performance of the SC. However, the structure–activity relationship between the internal structure of IGs and their SC properties is not fully understood. In the current study, the intuitive and regular structure–activity relationship between the structure and properties of IGs was revealed via combining computational simulation and experiment. In terms of conductivity, the ionic liquid (IL) ([EMIM][TFSI]) in the IG has a high self-diffusion coefficient calculated by molecular dynamics simulation (MDS), which is conductive to transfer and then improves the conductivity. The radial distribution function of the MDS shows that the larger the g(r) between the particles in the polymer network, the stronger the interaction. For stability, IGs based on [EMIM][TFSI] and [EOMIM][TFSI] ILs have higher density functional theory calculated binding energy, which is reflected in the excellent thermal stability and excellent capacitor cycle stability. Based on the internal pore size distribution and stress-strain characterization of the gel network ([ME3MePy][TFSI] and [BMIM][TFSI] as additives), the highly crosslinked aggregate network significantly reduces the internal mesoporous distribution and plays a leading role in improving the mechanical properties of the network. By using this strategy, it will be possible to design the ideal structure of the IG and achieve excellent performance.

Patterned ZnO nanorods/indium sulfide based self-powered photoelectrochemical photodetectors

The present work reports the excellent alignment of zinc oxide nanorod arrays (ZnO NRAs) patterned via the maskless lithography technique which was used as a photoanode material for photoelectrochemical (PEC) photodetection applications. The effects of circular patterns having different diameters, different gaps between circles, and the utilization of indium sulfide (In2S3) as a light-absorbing material in the visible region have been investigated in the PEC photodetector (PD) system in two different electrolytes. PEC PD performance evaluation confirmed the positive effect of patterned ZnO NRAs-based photoanode in the presence of In2S3, enhancing 982.9 μAcm−2 of current density (Jphoto), 54.6 mA/W of responsivity (Rs), 1.98 × 1011 Jones of detectivity (D*) and 8.18 × 104 of selectivity (S%) values. Besides, the best-performing patterned ZnO NRAs/In2S3 has been used to construct a quasi-solid state assembly using the prepared ionic-gel electrolyte and consequently, 2.19 × 1011 Jones of D* value has been observed. After all, the proposed PEC PD devices exhibited fast rise/decay times(τr/τd) in millisecond extent at 400 nm of wavelength.

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.

A Flexible and Self-Healing Ionic Gel Electrolyte Based on a Zwitterion (ZI) Copolymer for High-Performance Lithium Metal Batteries

Ionic gel electrolyte retains the characteristics of non-volatilization, non-flammability and outstanding electrochemical stability of ionic liquid, and shows good electrochemical performance combined with the excellent characteristics of different matrix materials, which is considered to be the best choice to achieve high energy density and safety at the same time. In this paper, a flexible and self-healing ionic gel electrolyte was prepared using a solvent-assisted method based on a zteric ion (ZI) copolymer. Abundant hydrogen bonds and synergistic interaction of ions in the electrolyte system endowed it with remarkable self-healing ability. An ionic conductivity of 9.06 × 10−4 S cm−1 at room temperature was achieved. Moreover, the lithium-ion transference number was increased to 0.312. The ionic gel electrolyte has a self-healing function which guarantees long-term tolerance during charging and discharging. The capacity retention rate of the Li//LiFePO4 battery was 96% after 155 cycles at 0.1 C at 60 °C. This polymer electrolyte is expected to solve the problem of increasing polarization, which is caused by the low lithium ions migration number in ionic liquid electrolyte. And ultimately, it gave rise to a good rate performance.

Localized Electron Density Regulation Effect for Promoting Solid-Liquid Ion Adsorption to Enhance Areal Capacitance of Micro-Supercapacitors.

The development of flexible microelectronic systems requires the construction of high-energy-output planar micro-supercapacitors (MSCs). Herein, the localized electron density, by introducing graphene quantum dots (GQDs) on the surface of electrodes, is regulated. The enhanced local field intensity promotes ion electrostatic adsorption at the solid-liquid interface, which significantly improves the energy density of MSCs in the confined space. Local electronic structure has been investigated from the perspective of the topological analysis of the electron localization function (ELF) and the electron density. Impressively, the edges of the simulated structure exhibit a higher electron density distribution than the CC skeleton. This finding indicates that the introduced GQDs reinforce the intrinsic electrical double-layer capacitance (EDLC) and the oxygen-bearing functional groups at the edge, further increasing the pseudocapacitance performance. Moreover, the edge electron aggregation effect enables the all-carbon-based symmetric MSCs to exhibit ultra-high areal capacitance (21.78mFcm-2 ) and excellent cycle stability (86.74% retention after 25000 cycles). This novel surface local charge regulation strategy is also applied for intensifying ion electrostatic adsorption on Zn-ion hybrid MSCs (polyvalent metal ions) and ion-gel electrolyte MSCs (non-metallic ions). With excellent planar integration, this device demonstrates excellent flexibility and has potential applications in timing and environmental monitoring.

Development of flame-retardant ion-gel electrolytes for safe and flexible supercapacitors

Development of flame-retardant ion-gel electrolytes for safe and flexible supercapacitors

Lithium-Ion Glass Gating of HgTe Nanocrystal Film with Designed Light-Matter Coupling.

Nanocrystals' (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm-2 and can be operated over a broad range of temperatures (130-300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W-1 or an external quantum efficiency of 500%) over a broadband spectral range.

Task-Specific Phosphonium Iongels by Fast UV-Photopolymerization for Solid-State Sodium Metal Batteries.

Sodium metal batteries are an emerging technology that shows promise in terms of materials availability with respect to lithium batteries. Solid electrolytes are needed to tackle the safety issues related to sodium metal. In this work, a simple method to prepare a mechanically robust and efficient soft solid electrolyte for sodium batteries is demonstrated. A task-specific iongel electrolyte was prepared by combining in a simple process the excellent performance of sodium metal electrodes of an ionic liquid electrolyte and the mechanical properties of polymers. The iongel was synthesized by fast (<1 min) UV photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of a saturated 42%mol solution of sodium bis(fluorosulfonyl)imide (NaFSI) in trimethyl iso-butyl phosphonium bis(fluorosulfonyl)imide (P111i4FSI). The resulting soft solid electrolytes showed high ionic conductivity at room temperature (≥10-3 S cm-1) and tunable storage modulus (104-107 Pa). Iongel with the best ionic conductivity and good mechanical properties (Iongel10) showed excellent battery performance: Na/iongel/NaFePO4 full cells delivered a high specific capacity of 140 mAh g-1 at 0.1 C and 120 mAh g-1 at 1 C with good capacity retention after 30 cycles.

Sodium Ion Flexible Battery in Poly-Acrylic Acid with Vinyl Silica Nano Particle Gel Electrolyte

Sodium Ion flexible battery in Poly-Acrylic Acid with Vinyl Silica Nano Particle Gel Electrolyte Sodium ion Battery(SIB) has much interesting due to abundance of sodium in earth's crust and low cost. To improve the performance of SIB with gel electrolyte, the poly-Acrylic Acid (PAA) cross-linked with Vinyl Silica Nano Particle (VSNP) was used as gel electrolyte hamper electrode material dissolution. The VSNP was used as cross-linker and synthesized by Sol-Gel method with Vinyltriethoxysilane (VTES) to improve the mechanical strength of gel. Fourier-Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) was used to analyze C=C bond and morphology of VSNP. PAA gel was polymerized by radical polymerizaiotn with VSNP cross-linker. To measure electrochemical property, SIHC was fabricated with Na3V2(PO4)3 (NVP) cathode material and Activated Carbon (YP50F) anode material. Electrochemical Impedance Spectroscopy (EIS) was used to analyze interfaces-contact with electrode and electrolyte. After measure electrochemical property, X-ray Diffraction was measured to characterize the NVP crystallinity. By this research, It can propose the way how apply to flexible sodium ion flexible battery and gel electrolyte

Wafer-scale microfabrication of flexible organic electrochemical transistors

We describe a photolithographic process to fabricate organic microdevices on flexible substrates that relies on photolithography and dry etching and is entirely compatible with standard cleanroom wafer processing equipment. A conductive polymer is used as active material to fabricate organic electrochemical transistors on a flexible polyimide substrate. The transistors are operated both with a solid-state ion gel electrolyte and an aqueous electrolyte, thus demonstrating their applicability as building blocks as both flexible integrated circuits and biosensors. Miniaturized transistors with 2 μm-long channels are also demonstrated to showcase the ability of the microfabrication process to define small features. We believe the proposed process flow offers a high resolution alternative to printing techniques by taking full advantage of the superior reliability of established semiconductor device manufacturing techniques and facilities.

One-step preparation of epoxy resin-based ionic gel electrolyte for quasi-solid-state lithium metal batteries

Quasi-solid-state lithium metal batteries have attracted wide attentions in recent years due to their high energy density, flexibility, and high safety. In this work, a novel epoxy resin-based ionic gel electrolyte (IGE) is synthesized via one-step curing polymerization of epoxy monomer and amine hardener with soft segments in the presence of ionic liquid electrolytes. The morphology and molecular structure of IGE are characterized by scanning electron microscopy, atomic force microscope and attenuated total reflection Fourier transform infrared. The amorphous microstructure and high thermal stability (≥270 °C) are identified by X-ray diffraction and thermogravimetric analysis. The obtained IGEs show high room temperature ionic conductivity from 0.05 mS cm−1 to 1.69 mS cm−1 due to the formation of dual continuous ionic conduction. In addition, the evolution of solid electrolyte interface (SEI) between IGE and lithium metal is investigated by electrochemical impedance spectroscopy, galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy. Finally, the Li/IGE/LiFePO4 cells can maintain a discharge capacity of 157 mAh g−1 at 0.1 C after 50 cycles at 60 °C and 132 mAh g−1 at 0.2 C after 150 cycles at room temperature.

The organic sodium salts/reduced graphene oxide composites as sustainable anode for solid-state sodium ion batteries

The organic molecule materials have attracted more attention on energy storage and conversion field, due to their green, low cost and sustainable. Nevertheless, the issues of low conductivity and high solubility in organic electrolyte limit their development for sodium ion batteries (SIBs). In this work, the Na 2 C 7 NO 4 H 3 (Na 2 PDA)/reduced graphene oxide (rGO) nanocomposites are prepared via a simple low cost method. The addition of rGO can enhance electroconductivity, and formation of sodium salt improve the problem of high solubility in organic electrolyte. The reasonable designs of sodium salt and construction of micro-nano structure endow it remarkable electrochemical peculiarities. As anode for SIBs, it delivers excellent rate capabilities. Besides, the solid-state SIBs are assembled using ionic gel electrolyte, and the Na 2 PDA/rGO electrode also demonstrates outstanding solid state electrochemical performance. • The Na 2 PDA/rGO composites are prepared via acid-base neutralization reaction. • The Na 2 PDA/rGO electrode delivers excellent rate capabilities. • Electrochemical mechanism and reaction kinetics of Na 2 PDA/rGO are explored. • The electrode exhibited good solid-state sodium storage performances.

Ion Pair Uptake in Ion Gel Devices Based on Organic Mixed Ionic–Electronic Conductors

AbstractIn organic mixed ionic–electronic conductors (OMIECs), it is critical to understand the motion of ions in the electrolyte and OMIEC. Generally, the focus is on the movement of net charge during gating, and the motion of neutral anion–cation pairs is seldom considered. Uptake of mobile ion pairs by the semiconductor before electrochemical gating (passive uptake) can be advantageous as this can improve device speed, and both ions can participate in charge compensation during gating. Here, such passive ion pair uptake in high‐speed solid‐state devices is demonstrated using an ion gel electrolyte. This is compared to a polymerized ionic liquid (PIL) electrolyte to understand how ion pair uptake affects device characteristics. Using X‐ray photoelectron spectroscopy, the passive uptake of ion pairs from the ion gel into the OMIEC is detected, whereas no uptake is observed with a PIL electrolyte. This is corroborated by X‐ray scattering, which reveals morphological changes to the OMIEC from the uptake of ion pairs. With in situ Raman, a reorganization of both anions and cations is then observed during gating. Finally, the speed and retention of OMIEC‐based neuromorphic devices are tuned by controlling the freedom of charge motion in the electrolyte.