Factors influencing fast ion transport in glyme-based electrolytes for rechargeable lithium–air batteries

Abstract

To elucidate the determination factors affecting Li-ion transport in glyme-based electrolytes, six kinds of 1.0 M tetraglyme (G4) electrolytes were prepared containing a Li salt (LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 , or LiN(SO 2 F) 2 ) or different concentrations (0.5, 2.0, or 2.7 M) of LiN(SO 2 CF 3 ) 2 . In addition to conventional bulk parameters such as ionic conductivity (s), viscosity (h), and density, self-diffusion coefficients of Li + , anions, and G4 were measured by pulsed-gradient spin-echo nuclear magnetic resonance method.Interaction energies (DE) were determined by density functional theory calculations based on the supermolecule method for Li + -anion (salt dissociation) and G4-Li + (Li + solvation) interactions. The DE values corresponded to ion diffusion radii formed by solvation and/or ion pairs. The order of dissociation energies DE was LiSO 3 CF 3 > LiN(SO 2 CF 3 ) 2 > LiN(SO 2 F) 2 , which agreed well with the dissociation degree of these salts in the electrolytes. From the obtained knowledge, we also demonstrated that increasing the mobility and number of carrier ions are effective ways to enhance s of glyme-based electrolytes by using 1,2-dimethoxyethane with lower h and similar dielectric constant to those of G4.

Quantitative Mapping of Molecular Substituents to Macroscopic Properties Enables Predictive Design of Oligoethylene Glycol-Based Lithium Electrolytes

“…The range of the molal conductivities of the 12 OEG–LiTFSI-based electrolytes at 353 K (0.0005–0.004 S cm –1 /mol kg –1 ) is consistent with the reported molar conductivity 52 of glyme–LiTFSI mixtures (0.5–3 S cm 2 mol –1 = 0.0005–0.003 S cm –1 /mol L –1 , 353 K, the density of OEG–salt mixtures is usually ∼1 kg L –1 ). 52 , 53 In addition, molal conductivity and viscosity are inversely correlated (see Figure S3 for the correlations between conductivity and molar viscosity, also known as Walden analysis), in agreement with data collected for glyme-based electrolytes as well. 52 , 54 , 55 Finally, introducing substituents was generally observed to lower molal ionic conductivity and increase viscosity compared to the parent octaglyme-based electrolyte.…”

“…The fitted E a of the octaglyme-based electrolyte (conductivity, 0.29 ± 0.02 eV; and viscosity, 0.29 ± 0.02 eV) is close to the reported values for related OEG-based electrolytes (e.g., E a of the conductivity of 2 M LiTFSI in tetraglyme was reported to be 0.34 eV). 53 Interestingly, E a for the octaglyme electrolyte is the lowest among the 12 oligomers, and the introduction of substituents leads to considerable increases in E a (the highest E a is 0.65 eV for conductivity and 0.66 eV for viscosity, both for benzenediboronic ester). The increase in E a across different oligomers is mirrored by the growth in A ( Figure S6 ), an effect known as the enthalpy–entropy compensation.…”

Quantitative Mapping of Molecular Substituents to Macroscopic Properties Enables Predictive Design of Oligoethyleneglycol-Based Lithium Electrolytes

“…The range of the molal conductivity of the 12 OEG-LiTFSI based electrolytes (0.0005−0.01 S cm −1 / mol kg −1 , 353 K) is consistent with the reported molar conductivity 50 of glyme-LiTFSI mixtures (0.5−3 S cm 2 mol −1 = 0.0005−0.003 S cm −1 / mol L −1 , 353 K, the density of OEG-salt mixtures are usually ~1 kg L −1 ). 50,51 In addition, molal conductivity and viscosity are inversely correlated (see Figure S3 for the correlations between conductivity and molar viscosity, also known as Walden analysis), in agreement with data collected for glyme-based electrolytes as well. 50,52,53 Finally, substituents were generally observed to lower molal ionic conductivity and increase viscosity compared to the parent octaglyme-based electrolyte.…”

“…The fitted Ea of the octaglyme-based electrolyte (conductivity: 0.29 ± 0.02 eV; and viscosity: 0.29 ± 0.02 eV) is close to the reported values for related OEG-based electrolytes (e.g., Ea of the conductivity of 2 M LiTFSI in tetraglyme was reported to be 0.34 eV). 51 Interestingly, Ea for the octaglyme electrolyte is the lowest among the 12 oligomers and the introduction of substituents leads to considerable increases in Ea (the highest Ea is 0.65 eV for conductivity and 0.66 eV for viscosity, both for benzenediboronic ester). The increase in Ea across different oligomers is mirrored by the growth in A ( Figure S6), an effect known as the enthalpy-entropy compensation.…”

In-Operando Detection of the Physical Property Changes of an Interfacial Electrolyte during the Li-Metal Electrode Reaction by Atomic Force Microscopy

“…The Li-ion concentration of the solution should affect the physical and chemical properties, such as the conductivity (σ), the self-diffusion coefficients (D), the viscosity (η), and the mass density (ρ). [22][23][24][25][26][27][28] Generally, these properties influence the electrochemical reaction of the electrodes, and especially the metal deposition is significantly affected. [29][30][31] Furthermore, the physical properties of the electrolyte provide the key to understand the solvation of Li-ions, which influence the electrochemical characteristics of the various negative electrodes as well as that of the Li metal.…”