Imide Ion Research Articles

Customized Li+ Solvation Sheath at the Poly(ethylene oxide)-Based Electrolyte/Ultrahigh-Nickel Cathode Interface toward Room-Temperature Solid-State Lithium Batteries.

The matching of poly(ethylene oxide) (PEO)-based electrolytes with ultrahigh-nickel cathode materials is crucial for designing new-generation high-energy-density solid-state lithium metal batteries (SLMBs), but it is limited by serious interfacial side reactions between PEO and ultrahigh-nickel materials. Here, a high-concentration electrolyte (HCE) interface with a customized Li+ solvation sheath is constructed between the cathode and the electrolyte. It induces the formation of an anion-regulated robust cathode/electrolyte interface (CEI), reduces the unstable free-state solvent, and finally achieves the compatibility of PEO-based electrolytes with ultrahigh-nickel cathode materials. Meanwhile, the corrosion of the Al current collector caused by lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ions is prevented by lithium difluoro(oxalato)borate (LiDFOB) ions. The synergistic effect of the double lithium salt is achieved by a well-tailored ratio of TFSI- and DFOB- in the first solvation sheath of Li+. Compared with reported PEO-based SLMBs matched with ultrahigh-nickel (Ni ≥ 90%) cathodes, the SLMB in this work delivers a high discharge specific capacity of 216.4 mAh g-1 (0.1C) even at room temperature. This work points out a direction to optimize the cathode/electrolyte interface.

A transferable classical force field to describe glyme based lithium solvate ionic liquids.

A non-polarizable force field for lithium (Li+) and bis(trifluoromethanesulfonyl)imide (TFSI-) ions solvated in diglyme at around 0.2 mol fraction salt concentration was developed based on abinitio molecular dynamics (AIMD) simulations and a modified polymer consistent force field model. A force-torque matching based scheme, in conjunction with a genetic algorithm, was used to determine the Lennard-Jones (LJ) parameters of the ion-ion and ion-solvent interactions. This force field includes a partial charge scaling factor and a scaling factor for the 1-4 interactions. The resulting force field successfully reproduces the radial distribution function of the AIMD simulations and shows better agreement compared to the unmodified force field. The new force field was then used to simulate salt solutions with glymes of increasing chain lengths and different salt concentrations. The comparison of the MD simulations, using the new force field, with experimental data at different salt concentrations and AIMD simulations on equimolar concentrations of the triglyme system demonstrates the transferability of the force field parameters to longer glymes and higher salt concentrations. Furthermore, the force field appears to reproduce the features of the experimental x-ray structure factors, suggesting accuracy beyond the first solvation shell, for equimolar salt solutions using both triglyme and tetraglyme as the solvent. Overall, the new force field was found to accurately reproduce the molecular descriptions of LiTFSI-glyme systems not only at various salt concentrations but also with glymes of different chain lengths. Thus, the new force field provides a useful and accurate tool to perform in silico studies of this family of systems at the atomistic level.

Ionic liquid-based self-healing gel electrolyte for high-performance lithium metal batteries

The gel electrolytes with self-healing function are being considered as promising replacement for traditional liquid electrolytes in lithium metal batteries due to their excellent battery safety, high energy density and minimum electrolyte damage. However, balancing self-healing, conductivity and mechanical properties remains a challenge for their practical application. Herein, a new ion liquid-based self-healing gel polymer electrolyte (IL-SHGPE) is introduced. The electrolyte was synthesized via UV-induced cross-linking of a polymer containing quadruple hydrogen bond units and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI) ion liquid. The resultant IL-SHGPE demonstrates exceptional self-healing ability (with 95% healing efficiency within 30 min), excellent thermal stability over a wide temperature range up to 410 °C. It also exhibits impressive mechanical strength with 41.3% elongation and 1.9 MPa tensile stress, room temperature ionic conductivity of 1.29 × 10−3 S/cm, and a wide electrochemical stability window of 5.18V (vs Li/Li+). Lithium metal batteries with this electrolyte showed an initial discharge capacity of 139 mAh g−1 at 1C rate, and a capacity retention of 88.3% after 200 cycles. Therefore, this work provides a significant exploration for balancing self-healing ability, mechanical attributes, and electrochemical performance of lithium batteries, and thus contributing valuable insights towards the development of high-performance self-healing gel electrolytes for lithium metal batteries.

Structural and Electronic Insights into 1-Ethyl-3-Methylimidazolium Bis(fluorosulfonyl)imide Ion Pair Conformers: Ab Initio DFT Study.

An understanding of the nature of molecular interactions among the ion pairs of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide [EMI[FSI]] can offer a starting point and significant insight into the more dynamic and multiple interactions within the bulk liquid state. In this context, close inspection of ion pair conformers can offer insight into the effects in bulk [EMI][FSI] liquid. The current work, therefore, gives a detailed analysis of the [EMI][FSI] ion pair conformers through analysis of the interaction energies, stabilization energies, and natural orbital of the ion pair conformers. The structures of the cations, anions, and cation-anion ion pairs of the conformers are optimized systematically by the ωB97X-D method with the DGDZVP basis sets, considering both the empirical dispersion corrections and the presence of a polar solvent, and the most stable geometries are obtained. The [FSI]- anions, unlike [TFSI]- anions, exist at the top position with respect to imidazolium rings. The presence of out-of-plane interactions between the [EMI]+ and [FSI]- ions is in good agreement with the stronger interactions of the [FSI]- anions with alkyl group hydrogens. The presence of out-of-plane conformers could also be related to the interaction of the anion with the π clouds of the [EMI]+ ring. In the [EMI]+ cation, the aromatic ring is π-acidic due to the presence of a positive charge in the N1-C1-N2 ring, which leads to the presence of [FSI]- anion donor [EMI]+ π-acceptor type interactions. The [EMI]+ cation and [FSI]- anions tend to form multiple σ* and π* interactions but reduce the strength of the individual contributions from a potential (linear) maximum. For the ion pair [EMI][FSI], the absolute value of the interaction energies is lower than the normal hydrogen bond energy (50 kJ/mol), which indicates that there is a very weak electrostatic interaction between the [EMI]+ cations and [FSI]- anions. The weaker attraction between the [EMI]+ and [FSI]- ions is suggested to contribute to the larger diffusion coefficients of the ions.

Structure and molecular interactions in 1‑ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ion pair conformers: abinitio DFT based study

Density functional theory (DFT) calculations with Grimme’s B97D functional including dispersion are employed to provide both structural and electronic insight into the multifold interactions occurring in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid [EMI][TFSI], which is currently being targeted for applications in next-generation Li-ion battery electrolytes. The geometric structure, interaction energy and natural bond orbital analysis of the ion-pair conformers of [EMI][TFSI] show differences from the conventional H-bonds. A total of six stable [EMI][TFSI] ion pair conformers were observed. Our results show that a doubly ionic H-bond exists between [EMI]+ and [TFSI]− ion pair conformers. The greater the number of multiple H-bond type interactions, the greater the absolute value of the interaction energy. Moreover, results from the NBO analysis show that, for [EMI][TFSI] ion pair conformers, charge transfer occurs mainly from the lone pairs of oxygen and nitrogen atom to the σ-type anti-bonding orbital of the C–H and π-type anti-bonding orbitals of N–C bonds. This was evident from the values of the stabilization energy E(2) associated with each electron delocalization from the donor to acceptor orbitals. There exist large numbers of multiple concomitant hydrogen bonds, but the values of the stabilization energy E(2) are generally small (E(2)n→\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ o$$\\end{document}σ* < 3 kcal/mol) for the individual H-bond interactions. The shorter the C–H···O and/or C–H···N bond is, the larger charge transfer, and the larger the stabilization energy E(2) associated with electron delocalization from donor to acceptor. Generally, the [EMI][TFSI] ion pair conformers tend to form multiple but bent H bonds, reducing the strength of the individual H bonds from a potential (linear) maximum.

Anion‐Stabilized Precursor Inks Toward Efficient and Reproducible Air‐Processed Perovskite Solar Cells

AbstractDespite the outperforming power conversion efficiency of low‐temperature and solution‐processed perovskite solar cells (PSCs) realized over the past decades, the undesirable stability from precursor inks to resultant devices and harsh preparation requirements still restrain their industrial production and practical deployment. Herein, an anion stabilization strategy is developed to achieve the comprehensive durability of perovskite photovoltaics throughout the whole two‐step air‐processed procedure. The effect of interionic bonding strengths on the ink properties, film crystallization, and photovoltaic performances is in‐depth explored and revealed. The pseudohalide bis(trifluoromethanesulfonyl)imide ions (TFSI−) not only improve the dispersion and stabilities of lead polyhalides and organic salt inks via strong electron‐withdrawing/donating chemical sites, but also realize high composition uniformity and preferential crystal growth of subsequent deposited perovskite layers by tuning the precursor reactivity and surface absorption. Ultimately, the optimizing PSCs deliver a superior efficiency of 24.16%, accompanied by notably improved long‐term stability toward extreme environmental and mechanical stimuli with lead leakage suppression. This work opens up a promising avenue toward reproducible air preparation of highly efficient, stable, and environmentally friendly perovskite optoelectronic devices via precise modulation of precursor properties.

Highly Crystalline Polyimide Covalent Organic Framework as Dual-Active-Center Cathode for High-Performance Lithium-Ion Batteries

Polyimide covalent organic framework (PI-COF) materials that can realize intrinsic redox reactions by changing the charge state of their electroactive sites are considered as emerging electrode materials for rechargeable devices. However, the highly crystalline PI-COFs with hierarchical porosity are less reported due to the rapid reaction between monomers and the poor reversibility of the polyimidization reaction. Here, we developed a water-assistant synthetic strategy to adjust the reaction rate of polyimidization, and PI-COF (COFTPDA-PMDA) with kgm topology consisting of dual active centers of N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA) and pyromellitic dianhydride (PMDA) ligands was successfully synthesized with high crystallinity and porosity. The COFTPDA-PMDA possesses hierarchical micro-/mesoporous channels with the largest surface area (2669 m2/g) in PI-COFs, which can promote the Li+ ions and bulky bis(trifluoromethanesulfonyl)imide (TFSI-) ions in organic electrolyte to sufficiently interact with the dual active sites on COF skeleton to increase the specific capacity of cathode materials. As a cathode material for lithium-ion batteries, COFTPDA-PMDA@50%CNT which integrated high surface area and dual active center of COFTPDA-PMDA with carbon nanotubes via π-π interactions gave a high initial charge capacity of 233 mAh/g (0.5 A/g) and maintains at 80 mAh/g even at a high current density of 5.0 A/g after 1800 cycles.

Macrocyclic Ionic Liquids with Amino Acid Residues: Synthesis and Influence of Thiacalix[4]arene Conformation on Thermal Stability.

Novel thiacalix[4]arene based ammonium ionic liquids (ILs) containing amino acid residues (glycine and L-phenylalanine) in cone, partial cone, and 1,3-alternate conformations were synthesized by alkylation of macrocyclic tertiary amines with N-bromoacetyl-amino acids ethyl ester followed by replacing bromide anions with bis(trifluoromethylsulfonyl)imide ions. The melting temperature of the obtained ILs was found in the range of 50-75 °C. The effect of macrocyclic core conformation on the synthesized ILs' melting points was shown, i.e., the ILs in partial&amp;nbsp;cone conformation have the lowest melting points. Thermal stability of the obtained macrocyclic ILs was determined via thermogravimetry and differential scanning calorimetry. The onset of decomposition of the synthesized compounds was established at 305-327 °C. The compounds with L-phenylalanine residues are less thermally stable by 3-19 °C than the same glycine-containing derivatives.

Highly Conductive and Underwater Stable Ionic Skin for All‐Day Epidermal Biopotential Monitoring

AbstractEpidermal biopotential monitoring is an essential part of wearable healthcare. For 24 × 7 h detection of electrophysiological signals, commercialized gel electrodes cannot satisfy the demands, in particular for monitoring in humidity or underwater. Epidermal electrodes that can be stable and operated underwater are required. Here, a highly conductive and optically camouflaged ionic skin for epidermal biopotential monitoring under aquatic circumstances is designed. There is a fluorine‐dipole interaction system consisting of fluorine‐rich segment in the polyurethane backbone and fluorine‐cation bonded 1‐ethyl‐3‐methylimidazolium bis(trifluoromethyl‐sulfonyl) imide ([EMIM]+ [TFSI]−) ion pairs distributed in the polymer matrix. Benefitting from the fluorine‐cation interaction, the ionic skin gains remarkable ionic conductivity (1.04 × 10−3 S cm−1), high optical transmittance (92%), and improved mechanical strength (3.1 MPa of Young's modulus). Via cations caught by fluorine‐rich segments, its ionic conductivity can keep stable even by rinsing or fierce washing in water. The epidermal electrode based on such ionic skin can accurately measure a variety of electrophysiological signals undboth atmospheric and aquatic environments, exhibiting robust and excellent signal quality. As the first demonstration of ionic skin‐based electrophysiological electrodes, the ionic skin paves a new way for all‐day wearable healthcare.

Mechanistic Insights into the Role of the Bis(trifluoromethanesulfonyl)imide Ion in Coevaporated p-i-n Perovskite Solar Cells.

Hybrid lead halide perovskites have reached comparable efficiencies to state-of-the-art silicon solar cell technologies. However, a remaining key challenge toward commercialization is the resolution of the perovskite device instability. In this work, we identify for the first time the mobile nature of bis(trifluoromethanesulfonyl)imide (TFSI-), a typical anion extensively employed in p-type dopants for 2,2'7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'spirofluorene (spiro-OMeTAD). We demonstrate that TFSI- can migrate through the perovskite layer via the grain boundaries and accumulate at the perovskite/electron-transporting layer (ETL) interface. Our findings reveal that the migration of TFSI- enhances the device performance and stability, resulting in highly stable p-i-n cells that retain 90% of their initial performance after 1600 h of continuous testing. Our systematic study, which targeted the effect of the nature of the dopant and its concentration, also shows that TFSI- acts as a dynamic defect-healing agent, which self-passivates the perovskite crystal defects during the migration process and thereby decreases nonradiative recombination pathways.

Easy-to-fabricate high efficiency silicon nanowires solar cell modified by CdTe and zinc tetraphenyl porphyrin nanostructures

Liquid junction solar cell (LJSC) with vertically silicon nanowires (SiNWs) as the primary photosensitizer, co-sensitized with luminescent and narrow gap CdTe nanoparticles, and cuboidal microstructures of zinc tetraphenyl porphyrin (ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency (PCE) of 9.09%, when combined with a polymeric gel of a I2/I− redox couple as the hole transport material and a counter electrode (CE) of poly(3,4-ethyelenedioxythiophene) doped with imide ions (PEDOT-N(CF3SO2)2), under 1 sun irradiance. The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance. Co-sensitization also supresses back electron transfer effectively, as is inferred from a ~68% enhancement in PCE compared to SiNWs alone. Optimization of the CE entailed the evaluation of the effect of dopant anion: imide versus dicyanamide in PEDOT, and revealed that the presence of macro-cracks in the polymer surface, a deeper work function, and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE, compared to imide. This study brings out how by judicious choice of photoanode and CE components, efficient, stable and easy-to-assemble LJSCs can be developed.

Development of highly durable retinal prosthesis using photoelectric dyes coupled to polyethylene film and quantitative in vitro evaluation of its durability

Retinal prostheses have been developed to restore vision in blind patients suffering from such diseases as retinitis pigmentosa. In our previous studies, we developed a retinal prosthesis called dye-coupled film by chemical coupling of photoelectric dyes, which absorb light and then generate electrical potential, with a polyethylene film surface. The dye-coupled film is nontoxic, and we recovered the vision of a monkey with macular degeneration. The amount of dye on the dye-coupled film, however, decreased to one-third after five months in the monkey’s eye. The photoelectric dye consists of a cation with photoresponsivity and a bromide ion (Br−). Therefore, an anion-exchange reaction could be applied to the dye-coupled film to improve its durability. In this study, the anion-exchange reaction was conducted using bis(trifluoromethanesulfonyl)imide ion (TFSI−), which has lower nucleophilicity than Br−. First, the long-term durability was examined without using animal subjects and in a short period. Subsequently, an elemental analysis was performed to confirm the exchange between Br− and TFSI−, and chemical properties, such as photoresponsivity and durability, before and after the anion exchange, were evaluated. It was quantitatively confirmed that the long-term durability of dye-coupled films can be evaluated in an in vitro environment and in a short period of one-thirtieth by utilizing a saline solution at 60 °C, compared with an in vivo environment. In addition, the durability of the dye-coupled film with TFSI− was improved to 270%–320% compared with that of the dye-coupled film with Br−.

Solid‐State Electrolyte Dielectrics Based on Exceptional High‐k P(VDF‐TrFE‐CTFE) Terpolymer for High‐Performance Field‐Effect Transistors

AbstractHigh‐performance and low‐voltage organic and inorganic field‐effect transistors (FETs) with solid‐state electrolyte gate insulator that is composed of an exceptional high‐k fluorinated dielectric and an ion‐gel‐blend polymer matrix are reported. The structuring polymer is high‐k poly(vinylidenefluoride‐trifluoroethylene‐chlorotrifluoroethylene) (P(VDF‐TrFE‐CTFE)) terpolymer. The ion gel is made of poly(vinylidene fluoride‐co‐hexafluroropropylene) (P(VDF‐HFP)) and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][TFSI]) ion liquid. The blend polymer matrix has high measured capacitance of ≈2 to 5.5 µF cm−2 at 100 Hz, which is attributed to formation of electrical double layers (EDLs) at the insulator/semiconductor interface. High effective carrier mobility (μeff) and low operating voltage ≤2 V with just 0.5 v% of P(VDF‐HFP)‐[EMIM][TFSI] solution in the bulk P(VDF‐TrFE‐CTFE) insulating layer are demonstrated, coupled with low gate‐leakage current levels. Excellent μeff = 1.30 ± 0.19 cm2 V−1 s−1 is achieved in P3HT FETs with SEGI, which is a remarkable boost from 0.48 ± 0.09 cm2 V−1 s−1 at 30 V when pure P(VDF‐TrFE‐CTFE) dielectric is used. Other semiconductors are also tested: IGZO has μeff = 11.09 ± 2.07 cm2 V−1 s−1, and PDFDT has μeff = 2.42 ± 0.46 cm2 V−1 s−1. These remarkable increases in mobility are attributed to the high concentration of induced carriers in the semiconducting channel.

Regulating the Inner Helmholtz Plane for Stable Solid Electrolyte Interphase on Lithium Metal Anodes.

The stability of a battery is strongly dependent on the feature of solid electrolyte interphase (SEI). The electrical double layer forms prior to the formation of SEI at the interface between the Li metal anode and the electrolyte. The fundamental understanding on the regulation of the SEI structure and stability on Li surface through the structure of the electrical double layer is highly necessary for safe batteries. Herein, the interfacial chemistry of the SEI is correlated with the initial Li surface adsorption electrical double layer at the nanoscale through theoretical and experimental analysis. Under the premise of the constant solvation sheath structure of Li+ in bulk electrolyte, a trace amount of lithium nitrate (LiNO3) and copper fluoride (CuF2) were employed in electrolytes to build robust electric double layer structures on a Li metal surface. The distinct results were achieved with the initial competitive adsorption of bis(fluorosulfonyl)imide ion (FSI-), fluoride ion (F-), and nitrate ion (NO3-) in the inner Helmholtz plane. As a result, Cu-NO3- complexes are preferentially adsorbed and reduced to form the SEI. The modified Li metal electrode can achieve an average Coulombic efficiency of 99.5% over 500 cycles, enabling a long lifespan and high capacity retention of practical rechargeable batteries. The as-proposed mechanism bridges the gap between Li+ solvation and the adsorption about the electrode interface formation in a working battery.

Self-healable electrochromic ion gels for low power and robust displays

Abstract Self-healable materials have a great potential to achieve durable and sustainable wearable electronic devices due to its inherent healing abilities, where cracks and rupture from reiterative bending and/or twisting operations can be healed and the electronic functions are restored. Most of the self-healable electronic devices reported to date are mainly focused on sensor, battery, super capacitor, and transistor. Electrochromic devices are introduced in diverse applications such as smart window, information display, and sensors due to the simple device configuration and a wide variety of material choice. Developing a material that simultaneously exhibits excellent electrochromic properties and self-healing behavior is still an unmet challenge. Herein, we report a self-healable ion gel for low power and robust electrochromic device by combination of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP)/poly(N,N-dimethylacrylamide) (PDMAA)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ion gel with ethyl viologen and ferrocene. Due to the high ion conductivity of ion gel, rapid redox response and low operating voltage of −1 V have been achieved. Moreover, the scratched EC ion gel was healed with minimal scarring and the healed device maintained transmittance contrast of ∼80% between bleached and colored states as well as the initial coloration efficiency of 74.84 cm2/C. Our results indicate that the ion gel has potential as a self-healable building block of low power and robust electrochromic displays and smart windows.

Atomistic Description of Ionic Diffusion in PEO–LiTFSI: Effect of Temperature, Molecular Weight, and Ionic Concentration

Understanding the ionic diffusion mechanism in polymer electrolytes is critical to the development of advanced lithium-ion batteries. We report here molecular dynamics-based characterization of structures and diffusion in poly(ethylene oxide) (PEO) with lithium and bis(trifluoromethysulfonyl)imide (TFSI) ions imbedded into the PEO structure. We consider a range of temperatures (360–480 K), molecular weights (43, 22, 10, and 2 chains with 23, 45, 100, and 450 EO monomers, respectively), and ion concentrations (r = 0.02, 0.04, 0.06, and 0.08 Li:EO) for which there is experimental data. The found dependence of the diffusion coefficients on these variables is in good agreement with experimental measurements. We then analyze how the diffusion performance depends on details of the atomistic diffusion mechanism, the motion of the Li and TFSI along the polymer chains and hopping between them, the role of polymer motion, the temperature dependence of the intrachain and interchain diffusion contributions to the tot...

Extraction of REE(III), U(VI), and Th(IV) from Nitric Acid Solutions with Carbamoylmethylphosphine Oxides in the Presence of Bis[(trifluoromethyl)sulfonyl]imide Ions

Extraction of microamounts of REE(III), U(VI), and Th(IV) with solutions of carbamoylmethylphosphine oxides (CMPOs) in organic diluents from aqueous HNO3 solutions containing lithium bis[(trifluoromethyl) sulfonyl]imide (LiTf2N) was studied. The efficiency of the REE(III), U(VI), and Th(IV) extraction from nitric acid solutions with CMPO solutions considerably increases in the presence of Tf2N– ions in the aqueous phase. The stoichiometry of the extractable complexes was determined, and the influence of the structure of the CMPO molecule, kind of organic diluent, and aqueous phase composition on the efficiency of the U(VI), Th(IV), and REE(III) extraction into the organic phase was considered.

Computational investigation of non-covalent interactions in 1-butyl 3-methylimidazolium/bis(trifluoromethylsulfonyl)imide [bmim][Tf2N] in EMD and NEMD.

Non-covalent interactions (NCIs) play a crucial role in the behavior and properties of ionic liquids (ILs). These interactions are particularly important for non-equilibrium properties such as the change in viscosity due to shearing forces (shear viscosity). Therefore, a detailed understanding of these interactions can improve our understanding of these important classes of liquids. Here, we have employed quantum mechanical energy decomposition analysis (EDA) and NCI analysis to investigate a series of representative 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) ion pairs extracted from classical equilibrium and non-equilibrium molecular dynamics simulations. EDA based on symmetry-adapted perturbation theory (SAPT) for the complete monomers, as well as fragment SAPT (FSAPT), for the functional fragments has been carried out. In general, the electrostatic component comprises ≈80% of the intermolecular interaction, and significant contributions from other components (induction and dispersion) are also observed, especially for interactions involving bifurcated hydrogen bonds. The FSAPT analysis suggests that caution is warranted when employing simplified assumptions for non-bonded interactions, e.g., focusing only on hydrogen bonds between functional fragments, since this view may not provide a complete picture of the complicated interactions between the ions. In non-equilibrium molecular dynamics, the total interaction energies of some fragments have a significant qualitative change as the shear rate increases. Our results indicate that the inter-fragment interactions play a fundamental role in the viscous behavior of ILs, suggesting that the exclusive use of geometric criteria to analyze inter-molecular interactions in these systems is not sufficient to investigate shear-thinning effects.

Electronic structure, spectral characteristics and physicochemical properties of linear, branched and cyclic alkyl group substituted 1-alkyl-3-butylimidazolium cation based ionic liquids

Room temperature ionic liquids (RTILs) composed of linear, cyclic or branched alkyl substituted 1-alkyl-3-butylimidazolium and bis{(trifluoromethyl)sulfonyl}imide (Tf2N) ion pairs have been modeled using the density functional theory. Electronic Structure, infrared and 1H NMR spectra of these ion pairs are presented. Calculated interaction energies accompanying the ion pair formation with varying alkyl substituent follows the order: isopentyl>n-pentyl>3-pentyl>cyclopentyl. The cation-anion binding in Tf2N ion pairs and those in their precursors composed of Br− ions are unraveled through the quantum theory of atoms in molecules and non-covalent interaction index reduced density gradient methods. The formation of Tf2N ion-pairs is governed by C-H⋅⋅⋅O hydrogen bonding, anion-π and electrostatic interactions from the imidazolium cation whereas the Br− ion pairs reveal dominance of the C∙∙∙Br orbital interactions. Use of natural bond orbital (NBO) analyses establish the correlation between the electron density in σ*(C-H) natural orbital and the observed decomposition temperature (Td) for the Tf2N based RTILs. Further a larger shift in vibrational frequency of the characteristic aromatic C-H stretching from the imidazolium cation in the infrared spectra suggests the lowered Td values.

Ionic liquid‐based organic–inorganic hybrid electrolytes: Impact of in situ obtained and dispersed silica

ABSTRACTOrganic–inorganic hybrid electrolytes based on PEO‐NaTFSI‐ionic liquid (HMIMTFSI)‐silica (in situ production via sol gel process) are being reported in this article. The variation in conductivity with ionic liquid (IL) addition has been explained on the basis of number of free TFSI anions evaluated using ATR‐IR data. The deconvolution of the IR spectra of these hybrid electrolytes has given evidence of ion‐pair formation which has been compared vis‐á‐vis the conductivity variation. The hybrid electrolyte with maximum conductivity comprises the highest number of free imide ions and has lowest glass transition temperature. FESEM has displayed a porous and layered surface morphology with dispersed silica nanoparticles. In addition, the optimized hybrid electrolyte has been compared with 5 wt% (limit of mechanical stability) ex situ silica added composite where the temperature cycling of conductivity has shown that the ex situ dispersed hybrid electrolytes do not retrace their conductivity path contrary to the in situ prepared hybrid electrolytes. This behavior has been explained to be due to the hindrance offered by the ex situ added silica in the recrystallization kinetics of PEO. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 207–218