Trifluoromethanesulfonate Anions Research Articles

Construction of Fluoride‐Rich Interphase for Sustained Magnesiophilic Site Release Toward High‐Stability Chloride‐Free Magnesium Metal Batteries

AbstractRechargeable magnesium batteries (RMBs) have the potentials in terms of high energy density, resource abundancy and safety beyond current lithium‐ion batteries. However, the bare Mg metal electrode is prone to be passivated by solvents, suffering from the extremely high overpotential and short life during cycling. Herein, a facile chloride‐free solution pretreatment method for Mg anode is developed to construct the fluoride‐rich artificial interphase. Driven by the strong‐Lewis‐acidity trifluoromethanesulfonate anion, the interphase consisting of magnesiophilic and fluoride‐rich components are constructed by the substitution reaction of Mg metal with antimony trifluoride. The formed porous Sb‐based skeletons can uniform the electric‐field distribution and Mg ions flux at anode side, inducing the self‐adapting dendrite‐free Mg deposition even under large current density. The generated alloyable metal fluoride enables to lower the desolvation energy barrier for Mg ions and sustainedly release metallic antimony to compensate for the potentially invalid magnesiophilic sites during cycling. Therefore the symmetric cells with modified Mg anodes achieve the excellent cycling over 2000 h at 1 mA cm−2 and under a high areal capacity of 5 mAh cm−2. The full cells with CuS cathodes exhibit a superior high voltage stability (2.6 V vs Mg/Mg2+) and high coulombic efficiency close to 100%.

Aggregation of positively charged poly(methyl methacrylate) latex particles in the presence of trifluoromethanesulfonate anion

Abstract We investigated the unique aggregation behavior of 3 types of positively charged poly(methyl methacrylate) (PMMA) latex particles in the presence of a trifluoromethanesulfonate (triflate) anion. The particles were prepared based on surfactant-free emulsion polymerization using azo radical initiators. The triflate anion was strongly adsorbed to surfaces of positively charged PMMA latex particles, as confirmed by electrophoresis. Additionally, its presence significantly reduced the critical coagulation concentration of the cationic PMMA latex particles compared with other anions.

Trifluoromethanesulfonate salt of 5,10,15,20-tetrakis(1-benzylpyridin-1-ium-4-yl)-21H,23H-porphyrin and its CaII complex

The synthesis, crystallization and characterization of a trifluoromethanesulfonate salt of 5,10,15,20-tetrakis(1-benzylpyridin-1-ium-4-yl)-21H,23H-porphyrin, C68H54N8 4+·4CF3SO3 −·4H2O, 1·OTf, are reported in this work. The reaction between 5,10,15,20-tetrakis(pyridin-4-yl)-21H,23H-porphyrin and benzyl bromide in the presence of 0.1 equiv. of Ca(OH)2 in CH3CN under reflux with an N2 atmosphere and subsequent treatment with silver trifluoromethanesulfonate (AgOTf) salt produced a red–brown solution. This reaction mixture was filtered and the solvent was allowed to evaporate at room temperature for 3 d to give 1·OTf. Crystal structure determination by single-crystal X-ray diffraction (SCXD) revealed that 1·OTf crystallizes in the space group P21/c. The asymmetric unit contains half a porphyrin molecule, two trifluoromethanesulfonate anions and two water molecules of crystallization. The macrocycle of tetrapyrrole moieties is planar and unexpectedly it has coordinated CaII ions in occupational disorder. This CaII ion has only 10% occupancy (C72H61.80Ca0.10F12N8O16S4). The pyridinium rings bonded to methylene groups from porphyrin are located in two different arrangements in almost orthogonal positions between the plane formed by the porphyrin and the pyridinium rings. The crystal structure features cation...π interactions between the CaII atom and the π-system of the phenyl ring of neighboring molecules. Both trifluoromethanesulfonate anions are found at the periphery of 1, forming hydrogen bonds with water molecules.

Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study.

Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([C4mim]+) and bis(trifluoromethanesulfonyl)amide ([TFSA]-) and trifluoromethanesulfonate ([OTf]-) anions. Experimental results are compared to the theoretical calculations for the electric double layer model. The hysteretic response of the RTIL/Pt interface derives predominantly from the activation energy of anion desorption, which causes the negative excess potential required for anion desorption. A comparison of the anion adsorption/desorption behaviors of neat RTILs with those of binary and diluted RTILs reveals that the large activation energy of anion desorption at the neat RTIL/Pt interface originates largely from the activation barrier for restructuring ionic layering in the diffuse layer.

New hydroxylammonium-based protic ionic liquids: Influence of cation and anion structure on thermal, viscosity and conductive properties

In the research work, new protic ionic liquids (Pr-ILs) were synthesized by an acid-base neutralization reaction. The influence of IL chemical structure (i.e. anion and cation nature) on the thermal behavior, viscosity and ionic conductivity was evaluated. To confirm the chemical structure of synthesized Pr-ILs, nuclear magnetic resonance (1H and 19F) and Fourier transform infrared spectroscopy analyses were performed. Thermal analysis demonstrated that the influence of anion nature on the IL thermal stability was more pronounced than that of cation. The ionic liquids with trifluoromethanesulfonate anion showed the highest thermal stability (Tdeg ∼ 410–420 °C) as compared with other studied anions (i.e. phosphate and acetate anions). The trifluoromethanesulfonate-based Pr-ILs also demonstrated high ionic conductivity – between ∼58 and ∼64 mS·cm−1 at 150 °C and non-humid conditions. Despite the fact that phosphate-based Pr-ILs were more thermally stable (Tdeg ∼ 250–280 °C) than acetate-based ones (Tdeg ∼ 215 °C), acetate-based Pr-ILs revealed a higher ionic conductivity (∼15–19 mS·cm−1 at 80 °C) than phosphate-based Pr-ILs (∼0.2–1 and ∼0.4–2 mS·cm−1 at 80 and 120 °C, respectively). The obtained results confirm that the synthesized Pr-ILs are promising candidates for using them in electrochemical applications, namely, electrodialysis and fuel cells.

Behavior, synthesis, and effectiveness of an activity of anilinium-based Ionic Liquids (AnILs) as a hardeners and modifiers for epoxy-coatings of flax biocomposites

This paper presents a comprehensive investigation of the synthesis and properties of anilinium-based ionic liquids (AnILs) incorporating dicyanamide [DCA] and trifluoromethanesulfonate [OTf] anions. This study systematically examines the thermal behavior of these AnILs, highlighting the influence of cation size on distinct thermal transitions. Crucially, detailed thermal analyses were conducted for both AnILs and their corresponding epoxy resin systems. AnILs featuring [DCA] anion exhibited lower enthalpy values, indicative of a gradual polymerization process with potential energy inefficiency. In contrast, AnILs with [OTf] anion displayed elevated enthalpy values, signifying accelerated polymerization and significant potential for crosslinking. The resulting epoxy coatings were subjected to meticulous mechanical analyses. Notably, AnILs with a dicyanamide anion exhibited a noteworthy correlation between increased strength, enhanced crosslinking, and heightened structural complexity. Conversely, anilinium-based ionic liquids with [OTf] anion displayed distinctive polymerization behavior, even at lower temperatures. Investigation of the curing mechanics uncovered distinct polymerization pathways influenced by factors such as anion strength, dealkylation initiation temperature, and structural branching. Tensile strength assessments of coatings with trifluoromethanesulfonate anion revealed intriguing behavior, indicating that additional reinforcement during curing, is essential for maintaining structural integrity in impact-prone scenarios. Moreover, this study proposed a novel mechanism involving residual aniline molecules that influence structural outcomes. Overall, this research provides valuable insights into the intricate interplay of AnILs structures, polymerization dynamics, and mechanical properties, providing a foundational understanding for future advancements in functional coating applications.

Regulating interfacial reaction through electrolyte chemistry enables gradient interphase for low-temperature zinc metal batteries

In situ formation of a stable interphase layer on zinc surface is an effective solution to suppress dendrite growth. However, the fast transport of bivalent Zn-ions within the solid interlayer remains very challenging. Herein, we engineer the SEI components and enable superior kinetics of Zn metal batteries under harsh conditions through regulating the sequence of interfacial chemical reaction. With the differences in chemical reactivity of trimethyl phosphate co-solvent and trifluoromethanesulfonate anions in the Zn2+-solvation shell, Zn3(PO4)2 and ZnF2 are successively generated on Zn metal surface to form a gradient ZnF2–Zn3(PO4)2 interphase. Mechanistic studies reveal the outer ZnF2 facilitates Zn2+ desolvation and inner Zn3(PO4)2 serves as channels for fast Zn2+ transport, contributing to long-term cycling at subzero temperatures. Impressively, the gradient SEI enables a high lifespan over 7000 hours in Zn symmetric cell and a capacity retention of 86.1% after 12000 cycles in Zn–KVOH full cell at –50 °C.

Anion-Incorporated Mg-Ion Solvation Modulation Enables Fast Magnesium Storage Kinetics of Conversion-Type Cathode Materials.

Rechargeable magnesium batteries (RMB) have emerged as one of the most promising alternatives to lithium-ion batteries due to the prominent advantages of magnesium metal anodes. Nevertheless, their application is hindered by sluggish Mg-ion storage kinetics in cathodes, although various structural modifications of cathode materials have been performed. Herein, an electrolyte design using an anion-incorporated Mg-ion solvation structure is developed to promote the Mg-ion storage reactions of conversion-type cathode materials. The addition of the trifluoromethanesulfonate anion (OTf- ) in the ether-based Mg-ion electrolyte modulates the solvation structure of Mg2+ from [Mg(DME)3 ]2+ to [Mg(DME)2.5 OTf]+ (DME = dimethoxy ethane), which facilitates Mg-ion desolvation and thus significantly expedites the charge transfer of the cathode material. As a result, the as-prepared CuSe cathode material on copper current collector exhibits a considerable increase in magnesium storage capacity from 61% (228 mAh g-1 ) to 95% (357 mAh g-1 ) of the theoretical capacity at 0.1 A g-1 and a more than twofold capacity increase at a high current density of 1.0 A g-1 . This work provides an efficient strategy via electrolyte modulation to achieve high-rate conversion-type cathode materials for RMBs. The incorporation of the trifluoromethanesulfonate anion in the Mg-ion solvation structure of the borate-based Mg-ion electrolyte enables the fast magnesium storage kinetics of the conversion-type cathode materials. The as-prepared copper selenide cathode achieved a more than twofold capacity increase at a high rate and the highest reversible capacities compared to those of the previously reported metal selenide cathodes.

Synergistic Defect Passivation by the Treatment of Ionic Liquids for Efficient and Stable Perovskite Solar Cells

The quality of perovskite films plays a crucial role in the performance of perovskite solar cells (Pero‐SCs) in terms of power conversion efficiency (PCE) and stability. Herein, an ionic liquid, tetra‐butylammonium trifluoromethanesulfonate (denoted TBASF), is used to treat perovskite films. The tetra‐butylammonium cation (TBA+) can bind the unreacted PbI2 and form a low‐dimensional material on the surface of the perovskite. This membrane improves the water resistance of the perovskite film. Meanwhile, trifluoromethanesulfonate anion (SF−) can passivate the uncoordinated Pb2+ and stabilize I− on the perovskite surface, which is beneficial to the stability of the devices. After the treatment, the Pero‐SCs achieve a champion PCE of 22.80% and excellent stability in highly humid conditions.

Crystal structure of cis(S),trans(O,N bpy)-(2,2′-bipyridyl-κ2 N,N′)bis(dimethyl sulfoxide-κS)[phenyl(pyridin-2-yl)methanone-κ2 N,O]ruthenium(II) bis(trifluoromethanesulfonate)

The molecular and crystal structures of the title complex, [Ru(C10H8N2)(C12H9NO)(C2H6OS)2](CF3O3S)2 or cis(S),trans(O,N bpy)-[Ru(bpy)(ppk)(dmso-S)2](OTf)2 {bpy = 2,2′-bipyridine, ppk = phenyl-2-pyridyl ketone [IUPAC nomenclature: phenyl(pyridine-2-yl)methanone], dmso = dimethyl sulfoxide, and OTf− = trifluoromethanesulfonate}, are reported. The Ru2+ ion has a distorted octahedral geometry with two bpy N atoms, the N and O atoms of ppk, and two S atoms of two cis dmso-S ligands. The carbonyl O atom of ppk is trans to bpy, and the N atom of pyridyl is trans to the dmso-S ligand [trans(O,N bpy) geometry]. One of the trifluoromethanesulfonate anions is disordered over three positions, with occupancies of 0.4, 0.4, and 0.2, respectively, in the refined model. The original disordered and SQUEEZE [Spek (2015). Acta Cryst. C71, 9–18] models were found to be almost equivalent, indicating that both the SQUEEZE and the original disordered model are satisfactory.

Dual-anion-coordinated solvation sheath for stable aqueous zinc batteries

Zinc (Zn) metal is a promising anode for aqueous batteries but is hindered by poor reversibility caused by dendrite growth and water-induced parasitic reactions (e.g., hydrogen evolution reaction and Zn corrosion). Here, a dual-anion-coordinated Zn2+-solvation sheath involving the trifluoromethanesulfonate (OTf−) anion and ethylenediaminetetraacetate (Y4−) anion is proposed to stabilize Zn anodes. Theoretical and experimental studies reveal that such a solvation structure not only weakens the water activity by decreasing the solvating-H2O content but also guides the homogeneous Zn2+ plating process. Moreover, this solvation structure enables the in-situ formation of an organic-inorganic solid-electrolyte interphase (SEI) on Zn derived by the decomposition of coordinated anions. This Zn2+-conducting SEI can isolate the active Zn from the bulk electrolyte and thus suppress water-induced side reactions. The tailored electrolyte composed of 1 M Zn(OTf)2 + 100 mM Na4Y enables high reversibility of Zn//Cu cell (99.7% Coulombic efficiency over 400 cycles at 1.0 mA cm−2) and long-term stability of Zn//Zn cell (over 1600 h at 1.0 mA cm−2 and 1.0 mAh cm−2), whilst it can well support the stable operation of Zn//VO2 full battery. This work provides an efficient electrolyte engineering strategy to improve the Zn reversibility and realize long-life aqueous batteries.

Scrutinizing the stability of haemoglobin in 1,2,4-triazolium based ionic liquid

In this work, N-1 substituted 1,2,4-triazolium-based cation and trifluoromethanesulfonate anion based IL has been synthesized and used as a solvent system to stabilize haemoglobin (Hb). The conformational stability of Hb at different concentrations of developed IL was inspected through spectroscopic techniques like UV–Vis, steady-state fluorescence, fluorescence time-correlated single photon counting (TCSPC), temperature dependent UV–Vis, fluorescence, and circular dichroism (CD). Hb structure is stabilized in the IL concentration range 0.001 to 0.01 M; Hb structure starts opening up in the IL concentration range 0.05 to 0.1 M; at 0.2 M IL concentration, denaturation of Hb takes place. Further, the nature of the interaction between IL and Hb was verified through a competitive hydrophobic fluorescence probe, 1-Anilino-8-Naphthalene Sulfonate (ANS), and it was observed that ANS does not interact with IL till 0.01 M IL concentration. Finally, the experiments illustrate that the IL concentration plays a significant role in stabilizing/destabilizing a particular protein.

(Battery Division Postdoctoral Associate Research Award Address Sponsored by MTI Corporation and the Jiang Family Foundation) Advances in Understanding the Rechargeable Zinc-air Batteries Chemistry

As a possible post lithium-ion battery technology, metal-air batteries have revived interest recently. Among the different types of metal-air batteries, rechargeable zinc-air battery (ZAB) is a promising electrochemical energy storage device with the advantages of potential low cost, high safety, environmental friendliness and high energy density. However, current ZAB still suffer from the strongly alkaline electrolyte, which is chemically unstable towards the active cathode material (ambient air) and to a large extent causes electrochemical irreversibility at the Zn metal anode. Zn metal in alkaline environment suffers from formation of high surface area dendrites, well known from Li metal anodes, non-uniform electrodeposition/-dissolution, and persistent corrosion that consumes electrolyte. On the cathode side, the reaction between alkaline electrolytes and CO2 in air produces insoluble carbonate salts, which irreversibly consumes electrolyte, and also physically clogs and chemically deactivates the porous air cathode. Since the redox reaction of O2 occurs via a sluggish 4e-(electron) oxygen reduction reaction (ORR) in conventional alkaline electrolytes, bi-functional catalysts have to be used on the cathode.Herein, specific attention is given to the obstacles caused by the conventional alkaline electrolytes with the focus on the fundamental understanding in battery chemistry. Recently, we demonstrated a previous-unknown reversible zinc peroxide (ZnO2)/O2 chemistry for the rechargeable ZAB.[1] By comparing the hydrophobicity of anions of Zn salts, we selected the hydrophobic trifluoromethanesulfonate (OTf-) anion with a large size as a constituent of the electrolyte solute. Comprehensive characterization and simulations identified the critical role of hydrophobic OTf- anions in dictating the electrochemical double layer structure that favors the formation of ZnO2 and suppression of H2O-involved reactions. Leveraging the high reversibility of both air cathode and Zn metal anode in the Zn(OTf)2 electrolyte, the Zn-air full cell demonstrated excellent cycling performance in ambient air despite a simple cell structure. Such tailoring of interfacial structures via electrolyte properties provides a solution to the electrochemical irreversibility that has been plaguing not only alkaline ZABs, but essentially all metal-air batteries for centuries, especially those with promising high theoretical energy densities using materials with abundance, but being only feasible in alkaline electrolytes as either primary or mechanically rechargeable batteries.Keywords: Energy Storage, Zn-air batteries, Electrolytes, Battery ChemistryReferences [1] Wei Sun, Fei Wang, Bao Zhang, Mengyi Zhang, Verena Küpers, Xiao Ji, Claudia Theile, Peter Bieker, Kang Xu, Chunsheng Wang, Martin Winter, A rechargeable zinc-air battery based on zinc peroxide chemistry, Science 371, (2021) 46-51.

Binary-Acid Catalysis with Sc(OTf)3/TfOH in the Alkenylation of Arenes with Alkynes.

Herein we report binary acid Sc(OTf)3/TfOH-catalyzed alkenylation of arenes with alkynes. In this system, the high-energy vinyl carbocations with activated and weakly coordinating trifluoromethanesulfonate anions by Lewis acid Sc(III) can undergo facile Friedel-Crafts reactions with arenes to give the desired adducts in up to 90% yield and with high Z-selectivity.

Structure and hydrogen bonding of mono-protic ionic liquids composed of N-alkylethylenediaminium cations and trifluoromethanesulfonate anion

The stabilities of some of the possible molecular structures, intermolecular hydrogen bonding interactions, and protonation sites of chelating mono-protic ionic liquids composed of N-alkyl (= Hexyl, Octyl, and 2-Ethylhexyl) ethylenediaminium cations with a trifluoromethanesulfonate anion (TFS), forming [HHex][TFS], [HOct][TFS] and [HEtHex][TFS] were studied using DFT calculations with the M06-2X functional and 6-311G(d, p) basis set. The BSSE-corrected interaction energies (∆E0BSSE) for the investigated structures range from − 98.3 to − 108.3 kcal mol−1. NBO and AIM analyses were applied to quantify the relative strengths of the hydrogen bonding interactions and to account for their effect on the stability of various molecular structures. The values of ∆E0BSSE decrease with increasing alkyl chain length and upon introduction of an ethyl branch in the cation. The second-order perturbation energy and electron density indicate that [HAlkyl]1＋[TFS] (protonated at the primary amine, Form A) are more stable than [HAlkyl]2＋[TFS] (protonated at the secondary amine, Form B).

Structure and dynamics of TiO2-anchored D205 dye in ionic liquids and acetonitrile

Molecular dynamics computer simulations of the solid-liquid interface of TiO2 and D205 dye (anchored or free) and solvent, such as ionic liquids (1-butyl-3-methylimidazolium with hexafluorophosphate (BmimPF6) and trifluoromethanesulfonate (BmimTFO) anions) or acetonitrile (ACN) are performed in the canonical (NVT) ensemble. For the solvent and TiO2, we used the force fields availabile in the literature or developed by us, while to described the TiO2 and D205 interactions, quantum-chemical calculations were carried out on a small size cluster of TiO2 where the D205 dye was anchored. The simulations were carried systematically in the absence or presence of the D205 dye. In the latter case, we consider the situation where the dye is covalently anchored or free at the interface. The solvent molecules, forming the first layers at the TiO2 interface, have been identified by analyzing the mass density distribution and radial distribution functions. The results show that the solvent molecules are structured in successive layers, the density of which decreases to reach that of the macroscopic one at a long distance normal to the TiO2 interface. These findings show also that the F and O atoms of the anions and the N atom of acetonitrile are at a close distance from the Ti or O atoms of the TiO2 surface, indicating a competition of the solvent and the dye to interact with these atoms. Furthermore, the time traces of the z-axis position of certain atoms of the anchored D205 dye did not show any substantial change suggesting the conformation change is not occurring in the time scale of 50 ns.

Water-soluble Ag(I)-based coordination polymers obtained by anion-directed self-assembly of various AgX salts and a phosphabetaine derived from 1,3,5-triaza-7-phophaadamantane

A new, solvent-free method has been developed for the synthesis of 7-(2-carboxy-ethyl)-1,3,5-triaza-7-(phosphoniatricyclo)[3.3.1.13,7]decane (L). It is disclosed here that 1,3,5-triaza-7-phosphaadamantane (PTA) reacted cleanly with acrylic acid in a planetary ball mill resulting in 88% yield of the corresponding P-carboxy-ethyl derivative, in striking contrast to the complete failure of the synthesis of the same product from the same reactants in solution. The resulting phosphabetaine, L gave crystalline 1D coordination polymers with Ag+-salts bearing PF6-, p-toluenesulfonate (tos) and trifluoromethanesulfonate (OTf) anions. According to single-crystal X-ray diffraction studies, the solid state structures of these coordination polymers were decisively influenced by the anion of the Ag+-salt used for synthesis. In addition to single-crystal X-ray diffraction, the new Ag-based coordination polymers, namely [Ag(μ3-L-κ3N:O:O’)]n(PF6)n, (1), [Ag(tos)(μ3-L-κ3N:N:O)]n·nH2O, (2), and [Ag(OTf)(μ3-L-κ3N:O:O’)]n, (3) were characterized also by elemental analysis, 1H-, 13C-, and 31P NMR, as well as IR spectroscopies and with ESI mass spectrometry. Determination of the hydrodynamic diameter of the phosphabetaine ligand and its Ag+-complexes by diffusion NMR measurements revealed, that upon dissolution in water these compounds did not retain their polymeric nature.

Electrocatalytic Water Oxidation with α-[Fe(mcp)(OTf)2] and Analogues

The complex α-[Fe(mcp)(OTf)2] (mcp = N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)-cyclohexane-1,2-diamine and OTf = trifluoromethanesulfonate anion) was reported in 2011 by some of us as an active water oxidation (WO) catalyst in the presence of sacrificial oxidants. However, because chemical oxidants are likely to take part in the reaction mechanism, mechanistic electrochemical studies are critical in establishing to what extent previous studies with sacrificial reagents have actually been meaningful. In this study, the complex α-[Fe(mcp)(OTf)2] and its analogues were investigated electrochemically under both acidic and neutral conditions. All the systems under investigation proved to be electrochemically active toward the WO reaction, with no major differences in activity despite the structural changes. Our findings show that WO-catalyzed by mcp–iron complexes proceeds via homogeneous species, whereas the analogous manganese complex forms a heterogeneous deposit on the electrode surface. Mechanistic studies show that the reaction proceeds with a different rate-determining step (rds) than what was previously proposed in the presence of chemical oxidants. Moreover, the different kinetic isotope effect (KIE) values obtained electrochemically at pH 7 (KIE ∼ 10) and at pH 1 (KIE = 1) show that the reaction conditions have a remarkable effect on the rds and on the mechanism. We suggest a proton-coupled electron transfer (PCET) as the rds under neutral conditions, whereas at pH 1 the rds is most likely an electron transfer (ET).

Understanding Structural and Transport Properties of Dissolved Li2 S8 in Ionic Liquid Electrolytes through Molecular Dynamics Simulations.

Lithium-sulfur batteries with high energy density are considered as one of the most promising future energy storage devices. However, the parasitic lithium polysulfides shuttle phenomenon severely hinders the commercialization of such batteries. Ionic liquids have been found to suppress the lithium polysulfides solubility, diminishing the shuttle effect effectively. Herein, we performed classical molecular dynamics simulations to explore the microscopic mechanism and transport behaviors of typical Li2 S8 species in ionic liquids and ionic liquid-based electrolyte systems. We found that the trifluoromethanesulfonate anions ([OTf]- ) exhibit higher coordination strength with lithium ions compared with bis(trifluoromethanesulfonyl)imide anions ([TFSI]- ) in static microstructures. However, the dynamical characteristics indicate that the presence of the [OTf]- anions in ionic liquid electrolytes bring faster Li+ exchange rate and easier dissociation of Li+ solvation structures. Our simulation models offer a significant guidance to future studies on designing ionic liquid electrolytes for lithium-sulfur batteries.

Anomalously high elastic modulus of a poly(ethylene oxide)-based composite electrolyte

The practical use of lithium metal anodes in solid-state batteries requires a polymer membrane with high lithium-ion conductivity, thermal/electrochemical stability, and mechanical strength. The primary challenge is to effectively decouple the ionic conductivity and mechanical strength of the polymer electrolytes. We report a remarkably facile single step synthetic strategy based on in-situ crosslinking of poly(ethylene oxide) (xPEO) in the presence of a woven glass fiber (GF). Such a simple method yields composite polymer electrolytes (CPE) of anomalously high elastic modulus up to 2.5 GPa over a broad temperature range (20 °C – 245 °C) that has never been previously documented. An unsupervised machine learning algorithm, K-mean clustering analysis, was implemented on the hyperspectral Raman mapping at the xPEO/GF interface. Using such a unique means, we show for the first time that the promoted mechanical strength originates from xPEO and GF interactions through dynamic hydrogen and ionic bonding. High ionic conductivity is achieved by the addition plasticizer (e.g. tetraglyme), where trifluoromethanesulfonate anions are tethered to the xPEO matrix and Li+ cations are favorably transported through coordination with the plasticizer. Further, stringent galvanostatic cycling tests indicates the CPE can be stably cycled for >3000 h in a Li-metal symmetric cell at a moderate temperature (nearly 1500 Coulombs/cm2 Li equivalents), outperforming most of the PEO-based electrolytes. The GF reinforced CPE reported here has multifunctional uses, such as solid electrolytes for all solid-state batteries and membranes for redox-flow batteries. Although the focus of this study is on lithium-based batteries, the results are equally promising for other alkali metal based batteries such as sodium and potassium.