The Mixing Effect of Glycylglycine with KCl, KBr, and Na2SO4 from Volumetric and Viscometric Investigations at 298.15 K

The mixing effect of a simple peptide such as glycylglycine, in the presence of aqueous electrolytes, has been studied by examining their volumetric and viscometric behavior. The increase in the apparent molar properties of both glycylglycine and electrolytes is attributed to the interactions present among cation, anion, the head groups of the peptide, and the peptide bond. Simple equations are developed to account for such interactions with a view to correlate apparent molar properties of glycylglycine and electrolyte in their aqueous mixtures. Transfer properties of both glycylglycine and electrolyte are investigated in order to understand the changes in the property of one component by the addition of another. These interactions are also supported by viscosity data, for which a simple model is developed to correlate the variation in viscosities with composition of a component.     

Diffusion of electrolytes of different natures through the cation-exchange membrane

Diffusion of different electrolytes through a negatively charged (cation-exchange) membrane into distilled water has been studied. It has been established theoretically (with no regard to the presence of diffusion layers) that the integral diffusion permeability coefficient of an electrolyte depends on the diffusion coefficients and the ratio between the charge numbers of a cation–anion pair, the ratio between the density of charges fixed in the membrane and electrolyte concentration, and the averaged coefficient of equilibrium distribution of cation?anion ion pairs in the membrane matrix. It has been found that, when co-ions have a higher mobility, the dependence of diffusion permeability on electrolyte concentration passes through a maximum. Derived equations have been compared with experimental dependences of the diffusion permeability of an MC-40 membrane with respect to different solutions of inorganic 1: 1 and 2: 1 electrolytes. The developed method has been shown to be applicable for describing diffusion of any electrolytes (including asymmetric ones) through arbitrary uniformly charged membranes.     

Synthesis of Low‐Viscosity Ionic Liquids for Application in Dye‐Sensitized Solar Cells

Two types of ionic liquids (ILs), 1‐(3‐hexenyl)‐3‐methyl imidazolium iodide and 1‐(3‐butenyl)‐3‐methyl imidazolium iodide, are synthesized by introducing an unsaturated bond into the side alkyl chain of the imidazolium cation. These new ionic liquids exhibit high thermal stability and low viscosity (104 cP and 80 cP, respectively). The molecular dynamics simulation shows that the double bond introduced in the alkane chain greatly changes the molecular system space arrangement and diminishes the packing efficiency, leading to low viscosity. The low viscosity of the synthesized ionic liquids would enhance the diffusion of redox couples. This enhancement is detected by fabricating dye‐sensitized solar cells (DSSCs) with electrolytes containing the two ILs and I₂. The highest efficiency of DSSCs is 6.85 % for 1‐(3‐hexenyl)‐3‐methyl imidazolium iodide and 5.93 % for 1‐(3‐butenyl)‐3‐methyl imidazolium iodide electrolyte, which is much higher than that of 5.17 % with the counterpart 1‐hexyl‐3‐methyl imidazolium iodide electrolyte.     

Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells: application for highly viscous electrolyte systems

To measure electron diffusion coefficients (D) and electron lifetimes (tau) of dye-sensitized solar cells (DSC), we introduced stepped light-induced transient measurements of photocurrent and voltage (SLIM-PCV), which can simplify the optical setup and reduce measurement time in comparison to conventional time-of-flight and frequency-modulated measurements. The method was applied to investigate the influence of the viscosity of a thermally stable high-boiling-point solvent on the energy conversion efficiency of DSCs. By systematic study of the influence of the viscosity, the species of cations as the counter charge of I(-)/I(3)(-), and the concentrations of electrolytes, we concluded that a lower dye cation reduction rate due to slower iodine diffusion is a limiting factor for a highly viscous electrolyte system. On the other hand, comparable values of D and increased values of tau were observed in a highly viscous electrolyte. By employing 0.5 M TBAI and 0.05 M I(2) in propylene carbonate, the efficiency of the DSC became comparable to that of a DSC using conventional electrolytes consisting of LiI, imidazolium iodide, and 4-tert-butylpyridine in methoxyacetonitrile. The simultaneous evaluation of D and tau through the appropriately simple measurement realizes fast optimization of the efficient and reliable DSC composed of thermally stable but often viscous electrolytes.     

Chemistry-Performance Relationships of Polymer Gel-Electrolytes for Mg−S and Li−S Batteries: Influence of Network Cation Solvation Capacity on Polymer-Polysulfide Interactions

Metal-sulfur batteries are a promising next-generation energy storage technology, offering high theoretical energy densities with low cost and good sustainability. An active area of research is the development of electrolytes that address unwanted migration of sulfur and intermediate species known as polysulfides during operation of metal-sulfur batteries, a phenomenon that leads to low energy efficiency and short life-spans. A particular class of electrolytes, gel polymer electrolytes, are especially attractive for their ability to repel polysulfides on the basis of structure, electrostatics, and other polymer properties. Herein, within the context of magnesium- and lithium-sulfur batteries, we investigate the impact of gel polymer electrolyte cation solvation capacity, a property related to network dielectric constant and chemistry, on sulfur/polysulfide-polymer interactions, an understudied property-performance relationship. Polymers with lower cation solvation capacity are found to permanently absorb less polysulfide active material, which increases sulfur utilization for Li−S batteries and significantly increases charge efficiency and life-span for Li−S and Mg−S batteries.     

Effect of the electrolyte concentration on cation binding in aqueous surfactant solutions.

Electrospray ionisation mass spectrometry (ESI-MS) is used for the qualitative and quantitative study of ion binding to interfaces. The ESI-MS measurements are carried out in aqueous solutions of sodium dodecyl sulphate (SDS) in the presence of NaCl, NH(4)ClO(4) , KCl, or Mg(ClO(4))(2) . The effect of the electrolyte concentration on the fractions, y(cation(+) ), of the DS(-) monomers bound to the cations is shown. Moreover, the binding stability of different cations with DS(-) monomers is determined versus the electrolyte concentration. This stability and the y(Na(+) ) values (the Na(+) ions derived from SDS), estimated in the presence of a given electrolyte, are quantitatively correlated with the electrolyte cation effect on the water structure. We also present calibration curves from which the molar concentrations of the sodium ions (derived from SDS) and of the other cations (derived from the electrolyte), bound to the SDS-micelle surface at a given electrolyte concentration, can be obtained. Besides, specific ion effects (Hofmeister effects) are considered for 1:1 electrolytes.     

Novel functionalized ionic liquid with a sulfur atom in the aliphatic side chain of the pyrrolidinium cation

A novel ionic liquid, never reported in literature until now, was properly designed, synthesized and preliminary investigated. This material was prepared combining the N-methylpyrrolidinium cation (PYR_1(2S1))⁺, exhibiting a sulfur atom in the alkyl side chain, with the bis(trifluoromethanesulfonyl)imide anion, (TFSI)⁻, to be addressed as safer electrolyte component for sulfur-based battery systems. The presence of sulfur within the cation side chain was found to prevent the crystallization of the ionic liquid even in the presence of lithium salt. Cyclic voltammetries have clearly indicated that Li⁺ cation exhibits good mobility and is reversibly plated/stripped in PYR_1(2S1)TFSI–LiTFSI electrolytes with high efficiency.     

Interactions of DL-serine and L-serine with NaCl and KCl in aqueous solutions

The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.     

Role of Hydrogen Bond Defects for Cluster Formation and Distribution in Ionic Liquids by Means of Neutron Diffraction and Molecular Dynamics Simulations

Defects fundamentally govern the properties of all real materials. Correlating molecular defects to macroscopic quantities remains a challenge, particularly in the liquid phase. Herein, we report the influence of hydrogen bonds (HB) acting as defects in mixtures of non-hydroxyl-functionalized ionic liquids (ILs) with an increasing concentration of hydroxyl-functionalized ILs. We observed two types of HB defects: The conventional HBs between cation and anion (c–a), and the elusive HBs between cations (c–c) despite the repulsive Coulomb forces. We use neutron diffraction with isotopic substitution in combination with molecular dynamics simulations for measuring the geometry, strength, and distribution of mobile OH defects in the IL mixtures. In principle, this procedure allows relating the number and stability of defects to macroscopic properties such as diffusion, viscosity, and conductivity, which are of utmost importance for the performance of electrolytes in batteries and other electrical devices.     

Evaluation of Electrochemical Stability of Sulfonated Anthraquinone-Based Acidic Electrolyte for Redox Flow Battery Application

Despite intense research in the field of aqueous organic redox flow batteries, low molecular stability of electroactive compounds limits further commercialization. Additionally, currently used methods typically cannot differentiate between individual capacity fade mechanisms, such as degradation of electroactive compound and its cross-over through the membrane. We present a more complex method for in situ evaluation of (electro)chemical stability of electrolytes using a flow electrolyser and a double half-cell including permeation measurements of electrolyte cross-over through a membrane by a UV–VIS spectrometer. The method is employed to study (electro)chemical stability of acidic negolyte based on an anthraquinone sulfonation mixture containing mainly 2,6- and 2,7-anthraquinone disulfonic acid isomers, which can be directly used as an RFB negolyte. The effect of electrolyte state of charge (SoC), current load and operating temperature on electrolyte stability is tested. The results show enhanced capacity decay for fully charged electrolyte (0.9 and 2.45% per day at 20 °C and 40 °C, respectively) while very good stability is observed at 50% SoC and lower, even at 40 °C and under current load (0.02% per day). HPLC analysis conformed deep degradation of AQ derivatives connected with the loss of aromaticity. The developed method can be adopted for stability evaluation of electrolytes of various organic and inorganic RFB chemistries.     

有机磷酸酯阻燃电解液的研究进展

随着锂离子电池的市场拓展,安全性问题已成为电动汽车、大规模储能等应用领域关注的首要问题. 目前商品化的锂离子电池普遍采用低沸点碳酸酯类电解液,其易燃性成为电池不安全性的主要隐患. 为了提高锂离子电池的本征安全性,阻燃或不燃性电解液成为近年来研究的热点,其中以磷酸酯为溶剂的阻燃型或不燃型电解液受到广泛关注. 本文主要介绍磷酸酯阻燃和不燃电解液的研究状况,分析了这类电解液与锂离子电池正负极的兼容性问题,讨论了改善磷酸酯电解液电化学兼容性的途径,提出了发展高效、安全、稳定的不燃电解液的一些思路.     

Electronic structure calculations on lithium battery electrolyte salts

New lithium salts for non-aqueous liquid, gel and polymeric electrolytes are crucial due to the limiting role of the electrolyte in modern lithium batteries. The solvation of any lithium salt to form an electrolyte solution ultimately depends on the strength of the cation-solvent vs. the cation-anion interaction. Here, the latter is probed via HF, B3LYP and G3 theory gas-phase calculations for the dissociation reaction: LiX <--> Li(+) + X(-). Furthermore, a continuum solvation method (C-PCM) has been applied to mimic solvent effects. Anion volumes were also calculated to facilitate a discussion on ion conductivities and cation transport numbers. Judging from the present results, synthesis efforts should target heterocyclic anions with a size of ca. 150 A(3) molecule(-1) to render new highly dissociative lithium salts that result in electrolytes with high cation transport numbers.     

Solution properties of polymers of pyridinium and ammonium methacrylates.

Solution properties of poly[1(2-hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2-hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.     

Combining Deep Eutectic Solvents with TEMPO-based Polymer Electrodes: Influence of Molar Ratio on Electrode Performance**

For sustainable energy storage, all-organic batteries based on redox-active polymers promise to become an alternative to lithium ion batteries. Yet, polymers contribute to the goal of an all-organic cell as electrodes or as solid electrolytes. Here, we replace the electrolyte with a deep eutectic solvent (DES) composed of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and N-methylacetamide (NMA), while using poly(2,2,6,6-tetramethylpiperidin-1-yl-oxyl methacrylate) (PTMA) as cathode. The successful combination of a DES with a polymer electrode is reported here for the first time. The electrochemical stability of PTMA electrodes in the DES at the eutectic molar ratio of 1 : 6 is comparable to conventional battery electrolytes. More viscous electrolytes with higher salt concentration can hinder cycling at high rates. Lower salt concentration leads to decreasing capacities and faster decomposition. The eutectic mixture of 1 : 6 is best suited uniting high stability and moderate viscosity.     

Solution properties of polymers of pyridinium and ammonium methacrylates

Solution properties of poly[1(2-hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2-hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.     

木质素磺酸钠对铅酸蓄电池胶体性能的影响

采用不同比例的木质素磺酸钠作为胶体电解质添加剂，探讨其添加前后胶体电解质的物理和电化学性能的变化。 粘度测试、老化析水量测试以及循环伏安和交流阻抗分析表明，添加剂能影响胶体粘度，减少老化析水量，提高胶体电化学性能和减少胶体电池内阻。 确定添加剂最佳添加量的质量分数为0.005%~0.01%，胶体电解质中气相二氧化硅的适宜质量分数为3.0%。 采用UV-Vis、FT-IR光谱、TEM和SEM对添加剂和胶体电解质的结构和形貌变化进行了表征。 结果表明，添加木质素磺酸钠的胶体电解质形成更为疏松多孔的结构，更有利于离子的传导和电解液的储存。     

The solvation structure,transport properties and reduction behavior of carbonate-based electrolytes of lithium-ion batteries

Despite the extensive employment of binary/ternary mixed-carbonate electrolytes (MCEs) for Li-ion batteries, the role of each ingredient with regards to the solvation structure, transport properties, and reduction behavior is not fully understood. Herein, we report the atomistic modeling and transport property measurements of the Gen2 (1.2 M LiPF₆ in ethylene carbonate (EC) and ethyl methyl carbonate (EMC)) and EC-base (1.2 M LiPF₆ in EC) electrolytes, as well as their mixtures with 10 mol% fluoroethylene carbonate (FEC). Due to the mixing of cyclic and linear carbonates, the Gen2 electrolyte is found to have a 60% lower ion dissociation rate and a 44% faster Li⁺ self-diffusion rate than the EC-base electrolyte, while the total ionic conductivities are similar. Moreover, we propose for the first time the anion–solvent exchange mechanism in MCEs with identified energetic and electrostatic origins. For electrolytes with additive, up to 25% FEC coordinates with Li⁺, which exhibits a preferential reduction that helps passivate the anode and facilitates an improved solid electrolyte interphase. The work provides a coherent computational framework for evaluating mixed electrolyte systems.

The different roles of the anion, cyclic and linear carbonates, and additive in mixed-carbonate electrolytes are revealed. The anion–solvent exchange mechanism and factors influencing the solid electrolyte interphase (SEI) formation are deciphered.