MD simulations of poly(ethylene oxide) (PEO) doped with lithium-bis(trifluoromethane)sulfonimide (LiTFSI) are analyzed with respect to the cation dynamics, the PEO dynamics as well as their coupling. Different cation transport mechanisms can be identified. These observations can be interpreted in terms of a recently proposed model of cation transport in polymer electrolytes. The model was capable of reproducing the lithium mean square displacement and self-diffusion coefficient. Because of the importance of interchain ion transfers for long-range ion transport, additional focus lies on the analysis of cations coordinated by two PEO chains, which is a common motif in this system.

Low concentrated aqueous ionic liquids (ILs) and their influence on protein structures have attracted a lot of interest over the last few years. This can be mostly attributed to the fact that aqueous ILs, depending on the ion species involved, can be used as protein protectants or protein denaturants. Atomistic molecular dynamics (MD) simulations are performed in order to study the influence of different aprotic ILs on the properties of a short hairpin peptide. Our results reveal distinct binding and denaturation effects for 1-ethyl-3-methylimidazolium (EMIM) in combination with different anions, namely, chloride (CL), tetrafluoroborate (BF4) and acetate (ACE). The simulation outcomes demonstrate that the studied ILs with larger anions reveal a more pronounced accumulation behavior of the individual ion species around the peptide, which is accomplished by a stronger dehydration effect. We can relate these findings to the implications of the Kirkwood-Buff theory, which provides a thermodynamic explanation for the denaturation strength in terms of the IL accumulation behavior. The results for the spatial distribution functions, the binding energies and the local/bulk partition coefficients are in good agreement with metadynamics simulations in order to determine the energetically most stable peptide conformations. The free energy landscapes indicate a decrease of the denaturation strength in the order EMIM/ACE, EMIM/BF4 and EMIM/CL, which coincides with a decreasing size of the anion species. An analysis of the potential binding energies reveals that this effect is mainly of enthalpic nature.

The lithium transport mechanism in ternary polymer electrolytes, consisting of PEO20LiTFSI and various fractions of the ionic liquid PYR13TFSI, is investigated by means of MD simulations. This is motivated by recent experimental findings 1 , which demonstrated that these materials display an enhanced lithium mobility relative to their binary counterpart PEO20LiTFSI. In order to grasp the underlying microscopic scenario giving rise to these observations, we employ an analytical, Rouse-based cation transport model 2 , which has originally been devised for conventional polymer electrolytes. This model describes the cation transport via three different mechanisms, each characterized by an individual time scale. It turns out that also in the ternary electrolytes essentially all lithium ions are coordinated by PEO chains, thus ruling out a transport mechanism enhanced by the presence of ionic-liquid molecules. Rather, the plasticizing effect of the ionic liquid contributes to the increased lithium mobility by enhancing the dynamics of the PEO chains and consequently also the motion of the attached ions. Additional focus is laid on the prediction of lithium diffusion coefficients from the simulation data for various chain lengths and the comparison with experimental data, thus demonstrating the broad applicability of our approach.

In Li/S and Mg/S batteries, the charge and discharge of the sulfur cathode proceeds through a cascade of bivalent S x 2– and radical S y •– polysulfide intermediates. The presence of Li+ or Mg2+ cations in the electrolyte determines the type of intermediates and the overpotentials of their formation in a different manner. Based on systematic cyclic voltammetry (CV) and UV/vis investigations, this work reveals how the mutual interplay of the different cations, the electrolyte solvent, and the polysulfide anions is reflected in the electrochemical behavior of “Li2S8”/LiTFSI and “MgS8”/MgTFSI2 solutions with dimethyl sulfoxide, dimethylformamide, acetonitrile, dimethoxyethane, tetraethylene glycol dimethyl ether, or tetrahydrofuran as solvent. It was observed that the disproportionation reactions of the polysulfides are generally more pronounced and especially the S3 •– radical is less stabilized in Mg2+ than in Li+ containing solutions. In contrast to their Li counterparts, the formation of S4 2– polysulfides during the reduction of sulfur is not observed in glyme-based Mg polysulfide solutions. Quantum chemical predictions of stability and disproportionation of the Mg/polysulfide/solvent clusters complemented the CV and UV/vis investigations.

We present an extensive molecular dynamics (MD) simulation study of the lithium ion transport in ternary polymer electrolytes consisting of poly(ethylene oxide) (PEO), lithium-bis(trifluoromethane)sulfonimide (LiTFSI), and the ionic liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethane)sulfonimide (PYR13TFSI). In particular, we focus on two different strategies by which the ternary electrolytes can be devised, namely by (a) adding the ionic liquid to PEO20LiTFSI and (b) substituting the PEO chains in PEO20LiTFSI by the ionic liquid. To grasp the changes of the overall lithium transport mechanism, we employ an analytical, Rouse-based cation transport model (Maitra et al. Phys. Rev. Lett. 2007, 98, 227802), which has originally been devised for binary PEO-based electrolytes. This model distinguishes three different microscopic transport mechanisms, each quantified by an individual time scale. In the course of our analysis, we extend this mathematical description to account for an entirely new transport mechanism, namely, the TFSI-supported diffusion of lithium ions decoupled from the PEO chains, which emerges for certain stoichiometries. We find that the segmental mobility plays a decisive role in PEO-based polymer electrolytes. That is, whereas the addition of the ionic liquid to PEO20LiTFSI plasticizes the polymer network and thus also increases the lithium diffusion, the amount of free, mobile ether oxygens reduces when substituting the PEO chains by the ionic liquid, which compensates the plasticizing effect. In total, our observations allow us to formulate some general principles about the lithium ion transport mechanism in ternary polymer electrolytes. Moreover, our insights also shed light on recent experimental observations (Joost et al. Electrochim. Acta 2012, 86, 330).

N-alkyl-N-alkyl pyrrolidinium-based ionic liquids (ILs) are promising candidates as non-flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs), but they present limitations in terms of lithium-ion transport, such as am uchl ower lithium transference number.T hus,apyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units.Weshow, by acombination of experimental characterizations and simulations,that the cationssolvating properties allow faster lithium-ion transport than alkyl-substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO,but also by enabling new conduction modes linked to the solvation of lithium by as ingle IL cation. This,c ombined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium-metal polymer batteries.

The dynamics of Li(+) transport in polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imde mixtures are investigated by combining neutron spin-echo (NSE) and dielectric spectroscopy with molecular dynamics (MD) simulations. The results are summarized in a relaxation time map covering wide ranges of temperature and time. The temperature dependence of the dc conductivity and the dielectric α relaxation time is found to be identical, indicating a strong coupling between both. The relaxation times obtained from the NSE measurements at 0.05 Å(-1)

We report the synthesis of solid polymer electrolytes (SPEs) using a thermally induced and a lithium salt catalyzed cationic ring-opening polymerization (CROP) technique. A synergistic approach using two salts such as lithium tetrafluoroborate-LiBF4 and lithium bis­(tri­fluo­ro­meth­ane sulfonyl)­imide-LiTFSI has assured a complete monomer to polymer conversion and fast reaction kinetics during the CROP process. The initiation mechanism of lithium salt-induced CROP is elucidated using molecular dynamic simulation, quantum chemical calculation, real-time FT-Raman spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetry–mass spectrometry analysis techniques. The cross-linked 3D network of ethylene oxide based SPE is prepared without the use of any solvents or external catalysts. In particular, a mixture of poly­(ethylene glycol) diglycidyl ether, LiBF4, and LiTFSI in appropriate proportions after a baking process produced a freestanding, flexible, and nontacky film. The synthesized SPEs exhibit low glass transition temperature (< −50 °C), high ionic conductivity (>0.1 mS cm–1), and excellent oxidation stability (>5.5 V vs Li/Li+). The SPE is polymerized directly onto a carbon-coated LiFePO4 cathode film and successfully cycled in a lithium metal battery configuration at 40 and 60 °C. As evidence, the SPE is galvanostatically cycled against a high-voltage LiNi1/3­Mn1/3­Co1/3O2 cathode, and the preliminary results indicated exciting characteristics in terms of specific capacity and Coulombic efficiency.