Recent Advances in Innovative Polymer Electrolytes based on Poly(ionic liquid)s

Wide-temperature solid polymer electrolytes: Li+ coordination structure, ionic transport and interphases

Solid-state batteries have gradually become a hotspot for the development of lithium-ion batteries due to their intrinsic safety and potential high energy density, among which, solid polymer electrolytes (SPEs) have attracted much attention due to the advantages of low cost, good flexibility and scalability for commercial application. However, the low ionic conductivity at room temperature, low mechanical strength and unstable interfaces of SPEs hinder further practical applications. In this paper, the modulation of the Li coordination structure and different ion transport channels in the wide-temperature range are reviewed. In addition, the effects of the Li coordination structure on the electrolyte/electrode interfaces/interphases and electrochemical performance are also presented. Furthermore, future research directions including coordination structure, ion transport, manufacturing techniques and full cell performance are summarized and an outlook is given, which will provide general principles to design safe and high-performance solid-state lithium batteries.

Ionogel Adhesives: From Structural Design to Emerging Applications

Adhesives are indispensable in both daily household applications and advanced industrial settings, where they must deliver exceptional bonding performance. Ionogel adhesives, which feature a supporting polymer network infused with ionic liquid (IL), have emerged as promising candidates due to their unique structural and functional properties. The presence of ionic species within ionogels promotes non-covalent interactions-such as ionic bonds, ion-dipole interactions, and hydrogen bonding-that enhance both cohesion within the material and adhesion to various substrates. These characteristics make ionogels ideal for applications that require robust adhesive performance, especially in demanding environments. Despite the growing interest in ionogel adhesives, a comprehensive review of the latest advancements in this area is lacking. This paper aims to fill this gap by categorizing ionogel adhesives based on their composition and discussing strategies to enhance their adhesive properties. Additionally, novel ionogel adhesives designed for specific applications are highlighted. Finally, the current state of research is summarized, and offers insights into the challenges and future opportunities for the development of ionogel adhesives.

Poly(Ionic) Liquid-Enhanced Ion Dynamics in Cellulose-Derived Gel Polymer Electrolytes

Gel polymer electrolytes (GPEs) are regarded as a promising alternative to conventional electrolytes, combining the advantages of solid and liquid electrolytes. Leveraging the abundance and eco-friendliness of cellulose-based materials, GPEs were produced using methyl cellulose and incorporating various doping agents, either an ionic liquid (1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [Pyr14][TFSI]), its polymeric ionic liquid analogue (Poly(diallyldimethylammonium bis(trifluoromethylsulfonyl)imide) [PDADMA][TFSI]), or an anionically charged backbone polymeric ionic liquid (lithium poly[(4-styrenesulfonyl)(trifluoromethyl(S-trifluoromethylsulfonylimino) sulfonyl) imide] LiP[STFSI]). The ion dynamics and molecular interactions within the GPEs were thoroughly analyzed using Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Heteronuclear Overhauser Enhancement Spectroscopy (HOESY), and Pulsed-Field Gradient Nuclear Magnetic Resonance Diffusion (PFG-NMR). Li+ transference numbers (tLi+) were successfully calculated. Our study found that by combining slow-diffusing polymeric ionic liquids (PILs) with fast-diffusing lithium salt, we were able to achieve transference numbers comparable to those of liquid electrolytes, especially with the anionic PIL, LiP[STFSI]. This research highlights the influence of the polymer's nature on lithium-ion transport within GPEs. Additionally, micro supercapacitor (MSC) devices assembled with these GPEs exhibited capacitive behavior. These findings suggest that further optimization of GPE composition could significantly improve their performance, thereby positioning them for application in sustainable and efficient energy storage systems.

All-Solid-State Lithium Metal Batteries with Microdomain-Regulated Polycationic Solid Electrolytes

Solid polymer electrolytes (SPEs) are promising for high-energy and high-safety solid-state lithium metal batteries (LMBs). Here, a polycationic solid electrolyte (PCSE) is described that leverages the inherent high thermal/chemical stability of the polycationic domain and the anion trapping (FMAT) effect of another fluorinated microdomain for stable and fast-charging high-voltage LMBs. Specifically, while the polycationic imidazolium backbone ensures high segmental flexibility facilitating the Li+ mobility, the fluorinated microdomain effectively traps the bis(trifluoromethanesulfonyl)imide anions by strong dipole interactions, imparting localized solvation and restricted mobility of the anions, as well as improved oxidation stability. As a result, the PCSE exhibits a high ionic conductivity of 1.4 mS cm-1, a high Li+ transference number of 0.50, and a wide electrochemical window of ∼5.5 V at 25 °C. By way of in situ thermal polymerization of the electrolyte within assembled cells, the PCSE enables ultra-stable cycling of Li|LiNi0.8Co0.1Mn0.1O2 cells with a capacity retention of 98.1% after 500 cycles at 0.2 C at ambient temperatures. The work on the molecular design of PCSEs represents a fundamentally unique perspective for the rational design of SPEs with balanced properties that are historically challenging for high-energy, long-life, ambient-temperature solid-state LMBs.

3D Printable Polymer Electrolytes for Ionic Conduction based on Protic Ionic Liquids

A range of protic ionic liquids (PILs) based on tri-n-alkylammonium cations and mesylate/triflate anions were incorporated into a polymer matrix to form ionogels (IGs). These systems were investigated for their thermal and electrochemical behaviour, as well as under the aspect of ion motion via PFG-NMR. The ionic conductivities of the ILs/IGs are in the range of 10-4-10-3 S/cm-1 at elevated temperatures and the diffusion coefficients are around 10-11 m2 s-1. Successful 3D printing of an IG with 70 wt % of IL is possible via stereolithography approaches, opening up applications in, e. g., structured ion-conductive membranes.

Converting a Metal-Coordinating Polymer to a Polymerized Ionic Liquid Improves Li+ Transport

Solid polymer electrolytes (SPEs) with mechanical strength and reduced flammability may also enable next-generation Li+ batteries with higher energy densities. However, conventional SPEs have fundamental limitations in terms of Li+ conductivity. While an imidazole functionalized polymer (PMS-Im) has been previously shown to have ionic conductivity related to the imidazole-Li+ coordination, herein we demonstrate that quaternization of this polymer to form an analogous imidazolium functionalized polymer (PMS-Im+) more efficiently solvates lithium salts and plasticizes the polymer. In addition, inverse Haven ratios as high as 10 indicate positively correlated Li+ transport, possibly due to percolation of nanochannels that significantly improve battery-relevant conductivity. From these combined effects, Li+ conductivity in PMS-Im+ (2.1 × 10-5 S/cm) is over an order of magnitude greater than in PMS-Im at 90 °C (1.6 × 10-6 S/cm).

Interfacial Constructing Poly(ionic liquids) on Nanoporous Block Copolymers for Antifouling Ultrafiltration

The remarkable flexibility in structural tunability and designability of poly(ionic liquids) (PILs) has garnered significant attention. Integration of PILs with membranes, novel properties, and functionalities is anticipated for applications in the fields of membrane separation. Here, we develop a facile method to prepare PIL-functionalized membranes in a one-step process by combining selective swelling-induced pore generation and ionic liquid functionalization. The block copolymer of poly(2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS, abbreviated as SDMA) films is immersed in a mixture of ethanol and bromopropane. In addition to the formation of nanoporous structures, an interfacial quaternization reaction between the PDMAEMA blocks and bromopropane occurs to generate poly(methacrylatoethyl propyl dimethylammonium bromide), resulting in the PIL-Br-functionalized membrane (SIL-Br) during the swelling process. It is noteworthy that bromopropane acting as a reactant also promotes the process of selective swelling. The water permeability of the resulting SIL-Br membrane is several times higher than that of the SDMA membrane, which is attributed to the increased pore size and significantly higher hydrophilicity of the SIL-Br membrane. In addition, the anion exchange of SIL-Br with l-proline (l-Pro) readily forms SIL-Pro-functionalized membranes (SIL-Pro), which exhibit exceptional electrical neutrality. Antifouling tests demonstrate that both SIL-Br and SIL-Pro have excellent resistance to proteins compared to the non-PIL-functionalization SDMA membrane, implying their great potential as antifouling membranes for water treatment.

Design of Highly Conductive PILs by Simple Modification of Poly(epichlorohydrin-co-ethylene oxide) with Monosubstituted Imidazoles

High ionic conductivity poly(ionic liquid)s (PILs) are of growing interest for their thermal and electrochemical stability, processability, and potential in safe, flexible all-solid-state electrochemical devices. While various approaches to enhance the ionic conductivity are reported, the influence of cation substituents is rarely addressed. Moreover, some of the asymmetric anions recently developed for high-conductivity ionic liquids were never tested in PILs. We report the design and synthesis of twelve novel cationic PILs prepared via quaternization of N-substituted imidazoles by commercially available poly(epichlorohydrin-co-ethylene oxide) (poly(EPCH-r-EO)) with subsequent ion metathesis. They differ by imidazolium side chain length (C1-C6 alkyl) and presence of heteroatoms (silyl, siloxane, and fluoroalkyl) and by anion type (bis(trifluoromethylsulfonyl)imide (TFSI), 2,2,2-trifluoromethylsulfonyl-N-cyanoamide (TFSAM), tetrafluoroborate (BF4), trifluoro(trifluoromethyl)borate (BF3CF3), and tricyanofluoroborate (BF(CN)3)). TFSI-based PILs with alkyl side chains gave lower glass transition temperatures (T g) and higher ionic conductivities than those bearing heteroatomic substituents, with n-butyl side chains providing a conductivity of 4.7 × 10-6 S cm-1 at 25 °C under anhydrous conditions. This increased to 1.0 × 10-5 and 4.5 × 10-4 S cm-1 at 25 and 70 °C, respectively, when the TFSI anion was replaced with BF(CN)3. All PILs showed good electrochemical (>3.2 V vs Ag+/Ag) and thermal (>185 °C) stability, making them excellent candidates for solid-state electrolytes in electrochemical devices.

A New (Trifluoromethane)Sulfonylimide Single-Ion Conductor with PEG Spacer for All-Solid-State Lithium-Based Batteries

The choice of ionic-liquid-like monomers (ILM) for single-ion conducting polyelectrolytes (SICPs) is crucial for the performance of all-solid-state lithium batteries. In the current study, we propose a novel approach for development of SICPs via design and synthesis of a new ILM with long poly(ethylene oxide) spacer between methacrylic group and (trifluoromethane)sulfonylimide anion. Its homopolymer shows an ionic conductivity that is ∼5 orders of magnitude higher (9.2 × 10-8 S cm-1 at 25 °C), in comparison with previously reported analogues, while the conductivity of its random copolymer with poly(ethylene glycol)methyl ethermethacrylate reaches the levels of 10-6 and 10-5 S cm-1 at 25 and 70 °C, respectively. The copolymer provides excellent thermal (T onset ≈ 200 °C) and electrochemical (4.5 V vs Li+/Li) stabilities, good compatibility with Li metal, and effective suppression of dendrite growth. Li/SICP/LiFePO4 cells are capable of reversibly operating at different C rates, demonstrating excellent Coulombic efficiency and retaining specific capacity upon prolonged charge/discharge cycling at a relatively high current rate (C/5) at 70 °C.

Dynamic Ion Gels from the Complex Coacervation of Oppositely Charged Poly(ionic liquid)s

A cationic poly(ionic liquid) (PIL) with pendent butyl imidazolium cations and free bis(trifluoromethylsulfonyl)imide (TFSI) anions and an anionic PIL with pendent TFSI anions and free 1-butyl-3-methylimidazolium cations are synthesized by postpolymerization chemical modification and reversible addition-fragmentation chain-transfer radical copolymerization, respectively. Upon mixing solutions of these two PILs in acetone with stoichiometric amounts of ion pairs, ionic exchanges induce coacervation and, after solvent evaporation, lead to the formation of a dynamic ion gel (DIG) and the concomitant release of free [1-methyl-3-butyl imidazolium]TFSI ionic liquid (IL). A comparison of thermal (Tg), ion conducting (σDC), and viscoelastic (elastic moduli (G')) properties for DIGs and their parent polyelectrolytes, as well as extracted and IL-doped DIGs, demonstrates the formation of ionic cross-links and the ability to easily produce polymer electrolytes with enhanced ionic conductivity (σDC up to 4.5 × 10-5 S cm-1 at 30 °C) and higher elastic moduli (G' up to 4 kPa at 25 °C and 1 rad s-1), making them highly desirable in many electrochemical applications, including supercapacitors, soft robotics, electrochromic devices, sensors, and solar cells.

Stretchable Iontronic Tactile Sensing Fabric

The iontronic tactile sensing modality has garnered significant attention due to its exceptional sensitivity, immunity to noise, and versatility in materials. Recently, various formats of iontronic tactile sensors have been developed, including droplets, polymer films, paper, ionic gels, and fabrics. However, the stretchability of the current iontronic pressure sensing fabric is inadequate, hindered by the limited stretchiness of the ionic functional fabric. Incorporating a stretchable tactile sensing implement could enhance the wear comfortability by preventing relative movement and ensuring intimate contact between the sensor and the skin. The research focuses on the development of a stretchable iontronic pressure sensing (SIPS) fabric for monitoring diverse aspects of body health and movement in wearable applications. The tactile sensing structure is generated at the iontronic interface between highly stretchable ionic and conductive fabrics. In particular, the ionic fabric is prepared by coating a layer of polyurethane/ionic liquid gel onto a Spandex fabric. To showcase its remarkable sensitivity, stretchability, and ability to detect diverse body information, several application scenarios have been demonstrated including an elastic wristband for precise pulse wave detection, a flexible belt with multitactile sensing channels for respiration and motion tracking purposes, and a stretchable fabric cuff equipped with a high-resolution sensing array comprising 32 × 32 units for accurate gesture recognition.

Piperazinium Poly(Ionic Liquid)s as Solid Electrolytes for Lithium Batteries

Poly(ionic liquid)s combine the unique properties of ionic liquids (ILs) within ionic polymers holding significant promise for energy storage applications. It is reported here the synthesis and characterization of a new family of poly(ionic liquid)s synthesized from cationic piperazinium ionic liquid monomers. The cationic poly(acrylamide piperazinium) in combination with sulfonamide anions like bis(trifluoromethanesulfonyl) imide (TFSI) and bis(fluorosulfonyl) imide (FSI) are characterized as solid polymer electrolytes. The polymer electrolytes in combination with pyrrolidonium ILs and LiFSI show high ionic conductivity, 5×10-3 S cm-1 at 100 °C. Piperazinium polymer electrolytes show excellent compatibility with lithium metal reversible plating and stripping at high current density and low temperature 40 °C.

1,3,4,5-Tetrasubstituted Poly(1,2,3-triazolium) Obtained through Metal-Free AA+BB Polyaddition of a Diazide and an Activated Internal Dialkyne

A tetra(ethylene glycol)-based 1,3,4,5-tetrasubstituted poly(1,2,3-triazolium) is synthesized in two steps including: i) the catalyst-free polyaddition of a diazide and an activated internal dialkyne and ii) the N-alkylation of the resulting 1,2,3-triazole groups. In order to provide detailed structure/properties correlations different analogs are also synthesized. First, parent poly(1,2,3-triazole)s are obtained via AA+BB polyaddition using copper(I)-catalyzed alkyne-azide cycloaddition or metal-free thermal alkyne-azide cycloaddition (TAAC). Poly(1,2,3-triazole)s with higher molar masses are obtained in higher yields by TAAC polyaddition. A 1,3,4-trisubstituted poly(1,2,3-triazolium) structural analog obtained by TAAC polyaddition using a terminal activated dialkyne and subsequent N-alkylation of the 1,2,3-triazole groups enables discussing the influence of the methyl group in the C-4 or C-5 position on thermal and ion conducting properties. Obtained polymers are characterized by 1H, 13C, and 19F NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, size exclusion chromatography, and broadband dielectric spectroscopy. The targeted 1,3,4,5-tetrasubstituted poly(1,2,3-triazolium) exhibits a glass transition temperature of -23 °C and a direct current ionic conductivity of 2.0 × 10-6 S cm-1 at 30 °C under anhydrous conditions. The developed strategy offers opportunities to further tune the electron delocalization of the 1,2,3-triazolium cation and the properties of poly(1,2,3-triazolium)s using this additional substituent as structural handle.

Highly Frustrated Poly(ionic liquid) ABC Triblock Terpolymers with Exceptionally High Morphology Factors

In this work, we report the successful synthesis of 17 unique compositions of a poly(ionic liquid) (PIL) ABC triblock terpolymer, poly(S-b-VBMIm-TFSI-b-HA), where S is styrene, VBMIm-TFSI is vinylbenzyl methylimidazolium bis(trifluoromethanesulfonyl)imide, and HA is hexyl acrylate. Nine distinct morphologies were observed, including two-phase and three-phase disordered microphase separated (D2 and D3), two-phase hexagonally packed cylinders (C2), core-shell hexagonally packed cylinders (CCS), three-phase lamellae (L3), two-phase lamellae (L2), core-shell double gyroid (Q230), spheres-in-lamellae (LSI), and a three-phase hexagonal superlattice of cylinders (CSL). The LSI morphology was unambiguously confirmed using small-angle X-ray scattering and transmission electron microscopy. Morphology type significantly impacted the ion conductivity of the PIL ABC triblock terpolymers, where remarkable changes in morphology factor (normalized ion conductivity) were observed with only small changes in the conducting volume fraction, i.e., PIL block composition. An exceptionally high morphology factor of 2.0 was observed from the PIL ABC triblock terpolymer with a hexagonal superlattice morphology due to the three-dimensional narrow, continuous PIL nanodomains that accelerate ion conduction. Overall, this work demonstrates the first systematic study of highly frustrated single-ion conducting ABC triblock terpolymers with a diverse set of morphologies and exceptionally high morphology factors, enabling the exploration of transport-morphology relationships to guide the future design of highly conductive polymer electrolytes.

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

The breadth and importance of polymerized ionic liquids (PILs) are steadily expanding, and this review updates advances and trends in syntheses, properties, and applications over the past five to six years. We begin with an historical overview of the genesis and growth of the PIL field as a subset of materials science. The genesis of ionic liquids (ILs) over nano to meso length-scales exhibiting 0D, 1D, 2D, and 3D topologies defines colloidal ionic liquids, CILs, which compose a subclass of PILs and provide a synthetic bridge between IL monomers (ILMs) and micro to macro-scale PIL materials. The second focus of this review addresses design and syntheses of ILMs and their polymerization reactions to yield PILs and PIL-based materials. A burgeoning diversity of ILMs reflects increasing use of nonimidazolium nuclei and an expanding use of step-growth chemistries in synthesizing PIL materials. Radical chain polymerization remains a primary method of making PILs and reflects an increasing use of controlled polymerization methods. Step-growth chemistries used in creating some CILs utilize extensive cross-linking. This cross-linking is enabled by incorporating reactive functionalities in CILs and PILs, and some of these CILs and PILs may be viewed as exotic cross-linking agents. The third part of this update focuses upon some advances in key properties, including molecular weight, thermal properties, rheology, ion transport, self-healing, and stimuli-responsiveness. Glass transitions, critical solution temperatures, and liquidity are key thermal properties that tie to PIL rheology and viscoelasticity. These properties in turn modulate mechanical properties and ion transport, which are foundational in increasing applications of PILs. Cross-linking in gelation and ionogels and reversible step-growth chemistries are essential for self-healing PILs. Stimuli-responsiveness distinguishes PILs from many other classes of polymers, and it emphasizes the importance of segmentally controlling and tuning solvation in CILs and PILs. The fourth part of this review addresses development of applications, and the diverse scope of such applications supports the increasing importance of PILs in materials science. Adhesion applications are supported by ionogel properties, especially cross-linking and solvation tunable interactions with adjacent phases. Antimicrobial and antifouling applications are consequences of the cationic nature of PILs. Similarly, emulsion and dispersion applications rely on tunable solvation of functional groups and on how such groups interact with continuous phases and substrates. Catalysis is another significant application, and this is an historical tie between ILs and PILs. This component also provides a connection to diverse and porous carbon phases templated by PILs that are catalysts or serve as supports for catalysts. Devices, including sensors and actuators, also rely on solvation tuning and stimuli-responsiveness that include photo and electrochemical stimuli. We conclude our view of applications with 3D printing. The largest components of these applications are energy related and include developments for supercapacitors, batteries, fuel cells, and solar cells. We conclude with our vision of how PIL development will evolve over the next decade.

Zwitterionic Polymer Ionogel Electrolytes Supported by Coulombic Cross-Links: Impacts of Alkali Metal Cation Identity

Zwitterionic (ZI) polymers enable the formation of noncovalent cross-links within ionic liquid electrolytes (ILEs) to create nonflammable, mechanically robust, and highly conductive ionogel electrolytes. In this study, ZI homopolymer poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] scaffolds are synthesized in situ within lithium and/or sodium salt-based ILEs to construct a series of ionogels that contain between 3 and 15 wt % poly(MPC). Room-temperature ionic conductivity values of these ionogels are found to vary between approximately 1.3 and 2.2 mS cm-1. For sodium only and 1:1 lithium/sodium equimolar mixed salt ionogels containing 6 wt % poly(MPC), the ionic conductivity is found to improve by 14% compared to the neat ILE due to the presence of the ZI scaffold. Moreover, comparing the elastic modulus values of lithium- versus sodium-containing ionogels revealed a difference of up to 1 order of magnitude [10.6 vs 111 kPa, respectively, for 3 wt % poly(MPC)]. Molecular dynamics simulations of ionogel precursor solutions corroborate the experimental results by demonstrating differences in the lithium/ZI monomer and sodium/ZI monomer cluster size distributions formed, which is hypothesized to influence the scaffold network cross-link density obtained upon photopolymerization. This work provides insights into why ZI polymer-supported ionogel properties that are relevant for the development of safer electrolytes for lithium-ion and sodium-ion batteries depend upon the chemical identity of the alkali metal cation.

Mechanisms of ion transport in lithium salt-doped zwitterionic polymer-supported ionic liquid electrolytes

Recent experimental results have demonstrated that zwitterionic ionogel comprised of polyzwitterion (polyZI)-supported lithium salt-doped ionic liquid exhibits improved conductivities and lithium transference numbers than the salt-doped base ionic liquid electrolyte (ILE). However, the underlying mechanisms of such observations remain unresolved. In this work, we pursued a systematic investigation to understand the impact of the polyZI content and salt concentration on the structural and dynamic properties of the poly(MPC) ionogel of our model polyZI ionogel, poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] supported LiTFSI/N-butyl-N-methylpyrrolidinium TFSI base ionic liquid electrolyte. Our structural analyses show strong lithium-ZI interaction consistent with the physical network characteristic observed in the experiments. An increase in polyZI content leads to an increased fraction of Li+ ions coordinated with the polyZI. In contrast, an increase in salt concentration leads to a decreased fraction of Li+ ions coordinated with the polyZI. The diffusivities of the mobile ions in the poly(MPC) ionogel were found to be lower than the base ILE in agreement with experiments at T > 300 K. Analysis of ion transport mechanisms shows that lithium ions within the poly(MPC) ionogel travel via a combination of structural, vehicular diffusion, as well as hopping mechanism. Finally, the conductivity trend crossover between the poly(MPC) ionogel and the base ILE was rationalized via a temperature study that showed that the base ILE ions are influenced more by the variation of temperature when compared to the poly(MPC) ions.

A Sustainable Gel Polymer Electrolyte for Solid-State Electrochemical Devices

Nowadays, solid polymer electrolytes have attracted increasing attention for their wide electrochemical stability window, low cost, excellent processability, flexibility and low interfacial impedance. Specifically, gel polymer electrolytes (GPEs) are attractive substitutes for liquid ones due to their high ionic conductivity (10^-3-10^-2 S cm^-1) at room temperature and solid-like dimensional stability with excellent flexibility. These characteristics make GPEs promising materials for electrochemical device applications, i.e., high-energy-density rechargeable batteries, supercapacitors, electrochromic displays, sensors, and actuators. The aim of this study is to demonstrate the viability of a sustainable GPE, prepared without using organic solvents or ionic liquids and with a simplified preparation route, that can substitute aqueous electrolytes in electrochemical devices operating at low voltages (up to 2 V). A polyvinyl alcohol (PVA)-based GPE has been cast from an aqueous solution and characterized with physicochemical and electrochemical methods. Its electrochemical stability has been assessed with capacitive electrodes in a supercapacitor configuration, and its good ionic conductivity and stability in the atmosphere in terms of water loss have been demonstrated. The feasibility of GPE in an electrochemical sensor configuration with a mediator embedded in an insulating polymer matrix (ferrocene/polyvinylidene difluoride system) has also been reported.

Nuclear Magnetic Resonance Relaxation Pathways in Electrolytes for Energy Storage

Nuclear Magnetic Resonance (NMR) spin relaxation times have been an instrumental tool in deciphering the local environment of ionic species, the various interactions they engender and the effect of these interactions on their dynamics in conducting media. Of particular importance has been their application in studying the wide range of electrolytes for energy storage, on which this review is based. Here we highlight some of the research carried out on electrolytes in recent years using NMR relaxometry techniques. Specifically, we highlight studies on liquid electrolytes, such as ionic liquids and organic solvents; on semi-solid-state electrolytes, such as ionogels and polymer gels; and on solid electrolytes such as glasses, glass ceramics and polymers. Although this review focuses on a small selection of materials, we believe they demonstrate the breadth of application and the invaluable nature of NMR relaxometry.

Comparison of olefin/paraffin separation by ionic liquid and polymeric ionic liquid stationary phases containing silver(I) ion using one-dimensional and multidimensional gas chromatography

Silver(I) ions have been used in various studies as components within polymer membranes or ionic liquids (ILs) to enable separation of olefins from paraffins. Polymeric ionic liquids (PILs) are a class of polymers synthesized from IL monomers and typically possess higher thermal and chemical stability than the ILs from which they are formed. Until now, very little is known about the difference in strength of silver(I) ion-olefin interactions when they take place in an IL compared to a PIL. In this work, the chromatographic separation of olefins by stationary phases composed of silver(I) bis[(trifluoromethyl)sulfonyl]imide ([Ag⁺][NTf₂^-]) incorporated into the 1-hexyl-3-methylimidazolium NTf₂ ([HMIM⁺][NTf₂^-]) IL and poly(1-hexyl-3-vinylimidazolium NTf₂) (poly([HVIM⁺][NTf₂^-])) PIL at varying concentrations was investigated. Olefins were more highly retained by silver(I) ions in PILs than in ILs as the silver(I) salt concentration in the stationary was increased. The potential separation power of silver(I)-containing IL and PIL stationary phases in comprehensive two-dimensional gas chromatography (GC×GC) was compared to the conventional one-dimensional system. The separation selectivity of alkenes and alkynes from paraffins was significantly increased, while dienes and aromatic compounds showed insignificant changes in retention. The chemical structural features of IL and PIL that enhance silver(I) ion stability and olefin separation were investigated by using silver(I) trifluoromethanesulfonate ([Ag⁺][OTf^-]), 1-decyl-3-methylimidazolium NTf₂ ([DMIM⁺][NTf₂^-]) IL, poly(1-decyl-3-vinylimidazolium NTf₂ (poly([DVIM⁺][NTf₂^-])) PIL, [HMIM⁺][OTf^-] IL and poly([HVIM⁺][OTf^-]) PIL. Longer alkyl substituents appended to the IL (and PIL) cation increased the strength of silver(I) olefin interaction, and [OTf^-] anions in the IL (and PIL) tended to preserve silver(I) ion from thermal reduction, while also retaining olefins less than the [NTf₂^-]-containing columns. In general, silver(I) ions in PILs possessing analogous chemical structures to ILs exhibited higher silver(I) ion-olefin interaction strength but were less thermally stable.

Mechanically Robust Poly(ionic liquid) Block Copolymers as Self-Assembling Gating Materials for Single-Walled Carbon-Nanotube-Based Thin-Film Transistors

The proliferation of high-performance thin-film electronics depends on the development of highly conductive solid-state polymeric materials. We report on the synthesis and properties investigation of well-defined cationic and anionic poly(ionic liquid) AB-C type block copolymers, where the AB block was formed by random copolymerization of highly conductive anionic or cationic monomers with poly(ethylene glycol) methyl ether methacrylate, while the C block was obtained by post-polymerization of 2-phenylethyl methacrylate. The resulting ionic block copolymers were found to self-assemble into a lamellar morphology, exhibiting high ionic conductivity (up to 3.6 × 10^-6 S cm^-1 at 25 °C) and sufficient electrochemical stability (up to 3.4 V vs Ag⁺/Ag at 25 °C) as well as enhanced viscoelastic (mechanical) performance (storage modulus up to 3.8 × 10⁵ Pa). The polymers were then tested as separators in two all-solid-state electrochemical devices: parallel plate metal-insulator-metal (MIM) capacitors and thin-film transistors (TFTs). The laboratory-scale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼10³ Hz and high areal capacitance (up to 17.2 μF cm^-2). For solid-state TFTs, low hysteresis was observed at 10 Hz due to the completion of EDL formation and the devices were found to have low threshold voltages of -0.3 and 1.1 V for p-type and n-type operations, respectively.

Temperature Effect on the Corrosion Inhibition of Carbon Steel by Polymeric Ionic Liquids in Acid Medium

In the present research work, the temperature effect on the corrosion inhibition process of API 5L X60 steel in 1 M H2SO4 by employing three vinylimidazolium poly(ionic liquid)s (PILs) was studied by means of electrochemical techniques, surface analysis and computational simulation. The results revealed that the maximal inhibition efficiency (75%) was achieved by Poly[VIMC4][Im] at 308 K and 175 ppm. The PILs showed Ecorr displacements with respect to the blank from −14 mV to −31 mV, which revealed the behavior of mixed-type corrosion inhibitors (CIs). The steel micrographs, in the presence and absence of PILs, showed less surface damage in the presence of PILs, thus confirming their inhibiting effect. The computational studies of the molecular orbitals and molecular electrostatic potential of the monomers suggested that the formation of a protecting film could be mainly due to the nitrogen and oxygen heteroatoms present in each structure.

Effect of the counterion size on microphase separation in charged-neutral diblock copolymers

In this work, the question of the influence of the counterion size on the self-assembly in melts of diblock copolymers with one charged block was studied using coarse-grained molecular dynamics simulations. It was assumed that the blocks were fully compatible, i.e., the Flory-Huggins parameter χ between them was equal to 0. Due to the presence of correlation attraction (electrostatic cohesion) between the charged species, the systems with all types of counterions underwent transitions to ordered states, forming various morphologies, including lamellae, perforated lamellae, and hexagonally packed cylinders. Phase diagrams were constructed by varying the chain composition f_c and locating the order-disorder transition positions in terms of the electrostatic strength parameter λ (dimensionless Bjerrum length). Despite having a rather large ion size mismatch, the systems with smaller counterions demonstrated an even better tendency to form microphase separated states than the systems with larger ones. It was found that the differences between the phase diagrams of the systems with different counterions can be roughly rationalized by using coordinates (volume fraction of the charged block φ_c-modified interaction parameter λ*). The latter parameter assumes that the electrostatic energy is simply inversely proportional to the characteristic distance between the ions of different signs. Such an approach appeared to be rather effective and allowed the diagrams obtained for different counterion sizes to almost coincide. The results of this work suggest that the counterion size can be used as a tool to control the system morphology as well as the effective incompatibility between the blocks.

Improvement of the Interface between the Lithium Anode and a Garnet-Type Solid Electrolyte of Lithium Batteries Using an Aluminum-Nitride Layer

The next generation of all-solid-state batteries can feature battery safety that is unparalleled among conventional liquid batteries. The garnet-type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO), in particular, is widely studied because of its high Li-ion conductivity and stability in air. However, the poor interface-contact between Li and the electrolyte (garnet) severely limits the development of solid electrolytes. In this study, we synthesize cubic phase Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) using a secondary sintering method. In addition, a thin aluminum nitride (AlN) layer is introduced between the metal (Li) and the solid electrolyte. Theoretical calculations show that AlN has a high affinity for Li. Furthermore, it is shown that the AlN coating can effectively reduce the interface impedance between Li and the solid electrolyte and improve the lithium-ion transport. The assembled symmetric Li cells can operate stably for more than 3600 h, unlike the symmetric cells without AlN coating, which short-circuited after only a few cycles. The hybrid solid-state battery with a modified layer, which is assembled using LiFePO₄ (LFP), still has a capacity of 120 mAh g⁻¹ after 200 cycles, with a capacity retention rate of 98%. This shows that the introduction of an AlN interlayer is very helpful to obtain a stable Li/solid-electrolyte interface, which improves the cycling stability of the battery.

A Computer Simulation Study of Thermal and Mechanical Properties of Poly(Ionic Liquid)s

Thermal and mechanical properties of poly(ionic liquid)s (PILs), an epoxidized ionic liquid-amine network, are studied via molecular dynamics simulations. The poly(ionic liquid)s are designed with two different ionic liquid monomers, 3-[2-(Oxiran-2-yl)ethyl]-1-{4-[(2-oxiran-2-yl)ethoxy]phenyl}imidazolium (EIM2) and 1-{4-[2-(Oxiran-2-yl)ethyl]phenyl}-3-{4-[2-(oxiran-2-yl)ethoxy]benzyl}imidazolium (EIM1), each of which is networked with tris(2-aminoethyl)amine, paired with different anions, bis(trifluoromethanesulfonyl)imide (TFSI⁻) and chloride (Cl⁻). We investigate how ionic liquid monomers with high ionic strength affect structures of the cross-linked polymer networks and their thermomechanical properties such as glass transition temperature (T_g) and elastic moduli, varying the degree of cross-linking. Strong electrostatic interactions between the cationic polymer backbone and anions build up their strong structures of which the strength depends on their molecular structures and anion size. As the anion size decreases from TFSI⁻ to Cl⁻, both T_g and elastic moduli of the PIL increase due to stronger electrostatic interactions present between their ionic moieties, making it favorable for the PIL to organize with stronger bindings. Compared to the EIM2 monomer, the EIM1 monomers and TFSI⁻ ions generate a PIL with higher T_g and elastic moduli. This attributes to the less flexible structure of the EIM1 monomer for the chain rotation, in which steric hindrance by ring moieties in the EIM1-based PIL enhances their structural rigidity. The π-π stacking structures between the rings are found to increase in EIM1-based PIL compared to the EIM2-based one, which becomes stronger with smaller Cl⁻ ion rather than TFSI⁻. The effect of the degree of the cross-linking on thermal and mechanical properties is also examined. As the degree of cross-linking decreases from 100% to 60%, T_g also decreases by a factor of 10–20%, where the difference among the given PILs becomes decreased with a lower degree of cross-linking. Both the Young’s (E) and shear (G) moduli of all the PILs decrease with degree of cross-linking, which the reduction is more significant for the PIL generated with EIM2 monomers. Transport properties of anions in PILs are also studied. Anions are almost immobilized globally with very small structural fluctuations, in which Cl⁻ presents lower diffusivity by a factor of ~2 compared to TFSI⁻ due to their stronger binding to the cationic polymer backbone.

Recent advances in poly(ionic liquid)s for biomedical application

Poly(ionic liquid)s (PILs) are polymers containing ions in their side-chain or backbone, and the designability and outstanding physicochemical properties of PILs have attracted widespread attention from researchers. PILs have specific characteristics, including negligible vapor pressure, high thermal and chemical stability, non-flammability, and self-assembly capabilities. PILs can be well combined with advanced analytical instruments and technology and have made outstanding contributions to the development of biomedicine aiding in the continuous advancement of science and technology. Here we reviewed the advances of PILs in the biomedical field in the past five years with a focus on applications in proteomics, drug delivery, and development. This paper aims to engage pharmaceutical and biomedical scientists to full understand PILs and accelerate the progress from laboratory research to industrialization.

Molecular dynamics investigation of charging process in polyelectrolyte-based supercapacitors

Supercapacitors are one of the technologically impressive types of energy storage devices that are supposed to fill the gap between chemical batteries and dielectric capacitors in terms of power and energy density. Many kinds of materials have been investigated to be used as supercapacitors' electrolytes to overcome the known limitations of them. The properties of polymer-based electrolytes show a promising way to defeat some of these limitations. In this paper, a simplified model of polymer-based electrolytes between two electrodes is numerically investigated using the Molecular Dynamics simulation. The simulations are conducted for three different Bjerrum lengths and a typical range of applied voltages. The results showed a higher differential capacitance compared to the cases using ionic-liquid electrolytes. Our investigations indicate a rich domain in molecular behaviors of polymer-based electrolytes that should be considered in future supercapacitors.

Immobilization of molecule-based ionic liquids: a promising approach to improve elecrocatalyst performance towards the hydrogen evolution reaction

Ionic liquids (ILs) have received continuous attention owing to their unique chemical and physical properties and to their successful integration in several applications.

Poly(ionic liquid) Based Composite Electrolytes for Lithium Ion Batteries

Polymerized ionic liquids (PIL) are an interesting substance class, which is discussed to transfer the outstanding properties and tunability of ionic liquids into a solid material. In this study we extend our previous research on ammonium based PIL and discuss the influence of additives and their usability as polymer electrolyte membranes for lithium ion batteries. The polymer electrolyte is thereby used as replacement for the commercially widespread system of a separator that is soaked with liquid electrolyte. The influence of the material composition on the ionic conductivity (via electrochemical impedance spectroscopy) and the diffusion coefficients (via pulsed-field-gradient nuclear magnetic resonance spectroscopy) were studied and cell tests with adapted membrane materials were performed. High amounts of the additional ionic liquid (IL) MPPyrr-TFSI (1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide) increased the ionic conductivity of the materials up to 1.3·10⁻⁴ S·cm⁻¹ but made the usage of a cross-linker necessary to obtain mechanically stable membranes. The application of liquid electrolyte mixtures with ethylene carbonate (EC) and MPPyrr-TFSI decreased ionic conductivity values down to the 10⁻⁹ S·cm⁻¹ range, but increased ⁷Li diffusion coefficients with increasing amounts of EC up to 1.7·10⁻¹⁰ m²·s⁻¹. Cell tests with two membrane mixtures proofed that it is possible to build electrolyte membranes on basis of the polymerized ionic liquids, but also showed that further research is necessary to ensure stable and efficient cell cycling.

Emerging iongel materials towards applications in energy and bioelectronics

In the past two decades, ionic liquids (ILs) have blossomed as versatile task-specific materials with a unique combination of properties, which can be beneficial for a plethora of different applications. The additional need of incorporating ILs into solid devices led to the development of a new class of ionic soft-solid materials, named here iongels. Nowadays, iongels cover a wide range of materials mostly composed of an IL component immobilized within different matrices such as polymers, inorganic networks, biopolymers or inorganic nanoparticles. This review aims at presenting an integrated perspective on the recent progress and advances in this emerging type of material. We provide an analysis of the main families of iongels and highlight the emerging types of these ionic soft materials offering additional properties, such as thermoresponsiveness, self-healing, mixed ionic/electronic properties, and (photo)luminescence, among others. Next, recent trends in additive manufacturing (3D printing) of iongels are presented. Finally, their new applications in the areas of energy, gas separation and (bio)electronics are detailed and discussed in terms of performance, underpinning it to the structural features and processing of iongel materials.

Development and Progression of Polymer Electrolytes for Batteries: Influence of Structure and Chemistry

Polymer electrolytes continue to offer the opportunity for safer, high-performing next-generation battery technology. The benefits of a polymeric electrolyte system lie in its ease of processing and flexibility, while ion transport and mechanical strength have been highlighted for improvement. This report discusses how factors, specifically the chemistry and structure of the polymers, have driven the progression of these materials from the early days of PEO. The introduction of ionic polymers has led to advances in ionic conductivity while the use of block copolymers has also increased the mechanical properties and provided more flexibility in solid polymer electrolyte development. The combination of these two, ionic block copolymer materials, are still in their early stages but offer exciting possibilities for the future of this field.