Ionic liquid-plasticized polymers: preparation processes, physicochemical properties, and proposed applications

Lithium batteries are the most attractive candidate to replace the traditional energy resources due to their high working voltage, high specific energy and long cycle life [1,2]. However, the widely use have been limited by their safety issues, especially under the condition of abusing or overcharging. In order to solve this issue, it is significant to screen a safe material as lithium batteries electrolyte.Room temperature ionic liquids (RTILs) have aroused much attention for use in lithium batteries, owing to their low volatility, inflammability, wide electrochemical window and high ionic conductivity [3]. Particularly, their excellent thermal stability makes them key to solve the safety issues of lithium batteries at high temperatures and their physicochemical properties can be tuned by introducing functionalized groups onto the cation or anion of RTILs. The functionalized task-special ionic liquids can reduce the viscosity and enhance their ionic conductivity of RTILs. In this study, a piperidinium-based ionic liquid, N-methyl-N-methoxycarbonylpiperidinium bis(trifluoromethanesulfonyl)imide ([MMOCPip][TFSI]), was synthesized by anion exchange reaction and used as an additive to electrolyte of Li-ion battery. The electrochemical performance of the electrolytes had been evaluated by electrochemical tests, such as the line sweep voltammetry, cyclic voltammetry and impedance spectroscopy.The N-methyl-N-methoxycarbonylpiperidinium bis(trifluoromethanesulfonyl)imide ([MMOCPip][TFSI]) ionic liquid was prepared by mixing equimolar N-methyl-N-methoxycarbonylpiperidinium bromide ([MMOCPip][Br]) and bis(trifluoromethanesulfonyl)imide lithium at room temperature in deionized water and by stirring for several hours until a hydrophobic [MMOCPip][TFSI] layer was formed below the water phase [4]. The ionic conductivity of [MMOCPip][TFSI] was 0.77 mS·cm-1 (25℃) and 2.41 mS·cm-1 (60℃), however, after adding 0.1 M LiTFSI, the ionic conductivity decreased to 0.51 mS·cm-1 (25℃) and 1.85 mS·cm-1 (60℃), respectively. The electrochemical window was 0.5 V~5.8 V (vs. Li+/Li), which was enough widely that could be used as common electrode material. The Li-ion transference number of ionic Liquid electrolyte containing 0.1 M LiTFSI was 0.56. The battery tests indicated that the [MMOCPip][TFSI] obviously improved the cyclability of the LiFePO4 cell. For the Li/ LiFePO4 half-cells, after 20 cycles at room temperature at 0.1 C, the discharge capacity was 109.7 mAh·g-1 with 98.7% capacity retention in the [MMOCPip][TFSI]/0.1 M LiTFSI electrolyte. The good electrochemical performance demonstrated that the [MMOCPip][TFSI] could be used as electrolyte additive for lithium batteries. Keywords: Ionic liquid; Li-ion battery; Ionic conductivity; Transference number Reference: [1] Wongittharoma N, Wang CH, Wang YC, Fey GTK, Li HY, Wu TY, Lee TC, Chang JK (2014). Charge-storage performance of Li/LiFePO4 cells with additive incorporated ionic liquid electrolytes at various temperatures. J Power Sources. 260: 268–275.[2] Yang J, Zhou XY, Zou YL, Tang JJ (2011). A hierarchical porous carbon material for high power, lithium ion batteries. Electrochim Acta. 56: 8576–8581.[3] Pandian S, Raju SG., Hariharan KS, Kolake SM, Park DH, Lee MJ (2015). Functionalized ionic liquids as electrolytes for lithium-ion batteries. J Power Sources. 286: 204-209. [4] Yang PX, Cui WY, Li LB, Liu L, An MZ (2012). Characterization and properties of ternary P(VdF-HFP)-LiTFSI-EMITFSI ionic liquid polymer electrolytes. Solid State Sciences. 14(5), 598–606. Figure 1

Electrolytes based on organic solvents used in current Li-ion batteries are not compatible with the next-generation energy storage technologies including those based on Li metal. Thus, there has been an increase in research activities investigating solid-state electrolytes, ionic liquids (ILs), polymers, and combinations of these. This Account will discuss some of the work from our teams in these areas. Similarly, other metal-based technologies including Na, Mg, Zn, and Al, for example, are being considered as alternatives to Li-based energy storage. However, the materials research required to effectively enable these alkali metal based energy storage applicationsis still in its relative infancy. Once again, electrolytes play a significant role in enabling these devices, and research has for the most part progressed along similar lines to that in advanced lithium technologies. Some of our recent contributions in these areas will also be discussed, along with our perspective on future directions in this field. For example, one approach has been to develop single-ion conductors, where the anion is tethered to the polymer backbone, and the dominant charge conductor is the lithium or sodium countercation. Typically, these present with low conductivity, whereas by using a copolymer approach or incorporating bulky quaternary ammonium co-cations, the effective charge separation is increased thus leading to higher conductivities and greater mobility of the alkali metal cation. This has been demonstrated both experimentally and via computer simulations. Further enhancements in ion transport may be possible in the future by designing and tethering more weakly associating anions to the polymer backbone. The second approach considers ion gels or composite polymer electrolytes where a polymerized ionic liquid is the matrix that provides both mechanical robustness and ion conducting pathways. The block copolymer approach is also demonstrated, in this case, to simultaneously provide mechanical properties and high ionic conductivity when used in combination with ionic-liquid electrolytes. The ultimate electrolyte material that will enable all high-performance solid-state batteries will have ion transport decoupled from the mechanical properties. While inorganic conductors can achieve this, their rigid, brittle nature creates difficulties. On the other hand, ionic polymers and their composites provide a rich area of chemistry to design and tune high ionic conductivity together with ideal mechanical properties.

Ionic systems in materials research : new materials and processes based on ionic polymerizations and/or ionic liquids

This work is focusing on the synthesis and application of new potential ionic liquids (ILs) for biodiesel production from waste palm cooking oil. For this propose total eleven ionic liquids were synthesized containing various types of cations and anions and characterized with nuclear magnetic resonance (NMR), fourier‐transform infrared (FTIR) and elemental analyser (CHNS). The Hammett acidity of the ionic liquids were determined using Ultraviolet ( UV ) visible spectrometer and correlated with their catalytic properties. The process of biodiesel preparation has been optimized with respect of different factors (catalysts concentrations, methanol to oil ratio, temperature, agitation speed and time) affecting the transesterification reaction. The highest yield of 96.25% for 3‐methyl‐1‐(4‐sulfo‐butyl)‐3H‐imidazol‐1‐ium trifluoromethanesulfonate [BSMIM][CF 3 SO 3 ] was obtained under optimal conditions. The obtained product was characterized using gas chromatography (GC), NMR, FTIR, Thermogravimetric analysis (TGA) techniques. The physicochemical properties like kinematic viscosity, flash point, density etc were determined and compared with the standard of American Society of Testing Materials (ASTM) and European Standard (EN) methods. The by‐product of reaction i.e. glycerol was further esterified to minimize the waste of glycerol. The kinetic study shows that the transesterification reaction catalysed by prepared ILs follow the pseudo‐first order reaction. The kinetic energy ( Ea ) of the reaction was calculated around 19.89 kJ/mol.

Effect of anion type in the performance of ionic liquid/poly(vinylidene fluoride) electromechanical actuators

Structural organization of ionic liquids embedded in fluorinated polymers

In recent years, the utilisation of ionic liquids supported on porous polymer membranes has been demonstrated to enhance gas separation performance by improving both permeability and selectivity for several industrially-relevant gas mixtures. However, the use of such supported ionic liquid membranes (SILMs) is normally not feasible at elevated process temperatures due to the resulting decrease in ionic liquid viscosity, which can lead to increased loss of ionic liquid from the membrane support during operation. In addition, many of the polymer membranes typically used in SILMs exhibit relatively poor mechanical and thermal stabilities at high temperatures. To overcome these problems associated with SILMs, thermally-stable composite ionic liquid and polymer membranes (CILPMs) have been fabricated in this study, thus exploiting the beneficial properties of ionic liquids for gas separation at elevated temperatures. Poly (pyromellitimide-co-4,4-oxydianiline) (PMDA-ODA PI) in combination with the ionic liquid, [C4mi [NTf2] were used to fabricate the CILPMs. A measurement rig was designed and built to determine permeabilities and selectivities of the CILPMs for H2, N2, CO, CO2 and CH4 over a range of pressures and temperatures. The fabricated CILPMs were shown to maintain excellent mechanical and thermal stability over a wide range of processing conditions. Temperature was shown to greatly affect both permeability and selectivity of the membranes, whilst pressure had less influence. The incorporation of [C4mi [NTf2] into the membranes was found to significantly increase CO2 permeation and, therefore, it is anticipated that these CILPMs hold significant potential for CO2 separation applications.

Molecular dynamics (MD) simulations have been performed for prototype models of polymer electrolytes in which the salt is an ionic liquid based on 1-alkyl-3-methylimidazolium cations and the polymer is poly(ethylene oxide), PEO. The MD simulations were performed by combining the previously proposed models for pure ionic liquids and polymer electrolytes containing simple inorganic ions. A systematic investigation of ionic liquid concentration, temperature, and the 1-alkyl- chain length, [1,3-dimethylimidazolium]PF6, and [1-butyl-3-methylimidazolium]PF6, effects on resulting equilibrium structure is provided. It is shown that the ionic liquid is dispersed in the polymeric matrix, but ionic pairs remain in the polymer electrolyte. Imidazolium cations are coordinated by both the anions and the oxygen atoms of PEO chains. Probability density maps of occurrences of nearest neighbors around imidazolium cations give a detailed physical picture of the environment experienced by cations. Conformational changes on PEO chains upon addition of the ionic liquid are identified. The equilibrium structure of simulated systems is also analyzed in reciprocal space by using the static structure factor, S(k). Calculated S(k) display a low wave-vector peak, indicating that spatial correlation in an extended-range order prevail in the ionic liquid polymer electrolytes. Long-range correlations are assigned to nonuniform distribution of ionic species within the simulation box.

Synthesis and properties of polymerized ionic liquids

Ionic liquid based Fluoropolymer solid electrolytes for Lithium-ion batteries

New polyethylene glycol (PEG)/ionic liquid aqueous biphasic systems (ABS) are presented. Distinct pairs of PEG polymers and ionic liquids can induce phase separation in aqueous media when dissolved at appropriate concentrations. Phase diagrams have been determined for a large array of systems at 298, 308 and 323 K. A comparison of the binodal curves allowed the analysis of the tunable structural features of the ionic liquid (i.e., anionic nature, cationic core, cationic alkyl side chain length and functionalisation, and number of alkyl substituents in the cation) and the influence of the molecular weight of the PEG polymer on the ability of these solutes to induce an ABS. It was observed that contrary to typical ABS based on ionic liquids and inorganic salts, in which the phase behaviour is dominated by the formation of the hydration complexes of the ions, the interactions between the PEG polymers and ionic liquids control the phase demixing in the polymer-type ABS studied herein. It is shown that both the ionic liquids and PEG polymers can act as the salting-out species; that is, it is an occurrence that is dependent on the structural features of the ionic liquid. For the first time, PEG/ionic liquid ABS are reported and insight into the major interactions that govern the polymer/ionic liquid phase behaviour in aqueous media are provided. The use of two different nonvolatile and tunable species (i.e., ionic liquids and PEG polymers) to form ABS allows the polarities of the phases to be tailored. Hence, the development of environmentally friendly separation processes that make use of these novel systems is envisaged.

Mechanistic studies of enhanced oil recovery by imidazolium-based ionic liquids as novel surfactants

Ionic liquids (ILs) hold great promise in many fields including energy storage and generation, mechanical, pharmaceutical, synthetic and separation applications to name just a few. For any given application, the desired physical properties of the ideal IL may differ substantially from others and no widely applicable patterns or trends to facilitate intuitive design. The origins of physical properties lie in the characteristics of the intermolecular energetics, which consist of a complex interplay between electrostatic and dispersion forces. This thesis investigates and develops computational methodologies for calculating a reliable description of the intermolecular interactions for this challenging class of solvents and electrolytes of the future. The electrostatic approximation used in classical molecular dynamics (MD) where atomic partial charges are assigned was investigated in terms of methods based on density matrix partitioning, and the restrained electrostatic potentials (RESP) approaches. It was found that the “geodesic” atomic partial charge scheme, part of the RESP family, produced the most accurate charges. This was measured in terms of (a) charge convergence with increasing basis set size; (b) charge invariance with changes to the coordinate system; (c) insensitivity to minor structural changes on the resulting charges; (d) adequate capture of charge transfer effects; and (e) the preservation of symmetric of charges in symmetric molecules. Although charges can vary dramatically depending on the scheme used, the careful use of atomic partial charge schemes may still produce reliable forcefields, or at least serve as a rapid diagnostic tool to quantify electrostatic interactions and charge transfer. In moving towards unbiased a priori descriptions of IL intermolecular interactions, second-order Moller-Plesset perturbation theory (MP2) was used with the linear-scaling fragment molecular orbital (FMO) framework to assess the extent to which dispersion forces play a role in the intermolecular energetics. ILs of increasing size were examined such that the many-body effects may be captured. The dispersion energy contribution formed up to 20% of the total interaction energy. Furthermore, the interaction energy as produced by FMO was within 1 kJ mol−1 of the full-wavefunction MP2 interaction energy when three-body effects were included. As the dispersion interaction is purely a quantum mechanical phenomenon, correlated quantum mechanical methods, such as MP2 or coupled-cluster approaches, are required to provide an unbiased account of these effects. Ab initio methods such as MP2 and CCSD(T) scale formally as N⁵ an N⁷, respectively, with chemical system size. While the FMO approach provides a marked improvement in efficiency, the counterpoise (CP) approach to correcting the basis set superposition error (BSSE) is not amenable to fragmented approaches and requires each ion in the cluster to be calculated in the basis set of the entire system. In order to remove this bottleneck, the spin-component scaled second-order Moller Plesset perturbation theory (SCS-MP2) methodology was refined by fitting 174 non-CP corrected interaction energies at the MP2/cc-pVTZ level of theory to CP corrected CCSD(T)/CBS benchmark energies. This has resulted in an implicit BSSE correction that may be used within the highly efficient FMO framework, and is shown to yield results on par with or exceeding the accuracy of MP2/cc-pVQZ for clusters of two and four ion pairs (IPs). This new approach as been termed SCS-IL-MP2. An alternative dispersion corrected density functional theory (DFT) approach, DFT- D3, was assessed and refined in view of producing accurate interaction energies at the same CCSD(T)/CBS quality. The same test set of 174 ILs was used to fit the SCS-IL-MP2 approach was used to refit the DFT-D3 approach for both the Hartree-Fock (HF) wavefunction and the PBE and BLYP density functionals (DFs). In most cases, the selection of the DF and associated DFT-D version 3 (DFT-D3) parameters differed negligibly with all reaching within 1 to 2 kJ mol−1 per IP. HF-D3 parameters, on the other hand, showed a substantial improvement, particularly when used with the Becke-Johnson (BJ) damping function. Refitted HF-D3 and the BJ damping function was able to consistently provide interaction energy errors below 5 kJ mol−1 per IP. It would be worthwhile further investigating the application of the refined HF-D3 in its ability to produce reliable energies and geometries over a more diverse set of ILs. Both the SCS-IL-MP2 and new DFT-D3 approaches may be applied to the highly scal- able FMO framework. These form the core elements of the quantum chemistry toolbox for the study and understanding of the physicochemical properties of ILs that have so far been only superficially characterised by electronic structure theory. From this starting point, a rigorous and unbiased a priori understanding of the intermolecular interactions and resulting physicochemical properties may be predicted by means of efficient ab initio molecular dynamics (AIMD) techniques.

Physicochemical properties and thermal-responsive phase separation of poly(ethylene glycol)-based ionic liquids

Due to their light weight, flexibility, and low energy consumption, ionic electroactive polymers have become a hotspot for bionic soft robotics and are ideal materials for the preparation of soft actuators. Because the traditional ionic electroactive polymers, such as ionic polymer-metal composites (IPMCs), contain water ions, a soft actuator does not work properly upon the evaporation of water ions. An ionic liquid polymer gel is a new type of ionic electroactive polymer that does not contain water ions, and ionic liquids are more thermally and electrochemically stable than water. These liquids, with a low melting point and a high ionic conductivity, can be used in ionic electroactive polymer soft actuators. An ionic liquid gel (ILG), a new type of soft actuator material, was obtained by mixing 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hydroxyethyl methacrylate (HEMA), diethoxyacetophenone (DEAP) and ZrO2 and then polymerizing this mixture into a gel state under ultraviolet (UV) light irradiation. An ILG soft actuator was designed, the material preparation principle was expounded, and the design method of the soft robot mechanism was discussed. Based on nonlinear finite element theory, the deformation mechanism of the ILG actuator was deeply analyzed and the deformation of the soft robot when grabbing an object was also analyzed. A soft robot was designed with the soft actuator as the basic module. The experimental results show that the ILG soft robot has good driving performance, and the soft robot can grab a 105 mg object at an input voltage of 3.5 V.