Solid-state electrolytes are the key to the development of lithium-based batteries with dramatically improved energy density and safety. Inspired by ionic channels in biological systems, a novel class of pseudo solid-state electrolytes with biomimetic ionic channels is reported herein. This is achieved by complexing the anions of an electrolyte to the open metal sites of metal-organic frameworks (MOFs), which transforms the MOF scaffolds into ionic-channel analogs with lithium-ion conduction and low activation energy. This work suggests the emergence of a new class of pseudo solid-state lithium-ion conducting electrolytes.

Creating Lithium-Ion Electrolytes with Biomimetic Ionic Channels in Metal–Organic Frameworks

On the difference in cycling behaviors of lithium-ion battery cell between the ethylene carbonate- and propylene carbonate-based electrolytes

https://ir.nctu.edu.tw:443/bitstream/11536/28534/1/000177955400028.pdf

Ionic conductivity enhancement of the plasticized PMMA/LiClO4 polymer nanocomposite electrolyte containing clay

Fourier-transform infrared (FTIR) and time-resolved IR spectroscopies have been used to study vibrational band positions, vibrational energy relaxation (VER) rates, and reorientation times of anions in several ionic liquid (IL) solutions. The ILs primarily investigated are based on the 1-butyl-2,3-dimethylimidazolium ([BM(2)IM]) cation with thiocyanate (NCS-), dicyanamide (N(CN)2-), and tetrafluoroborate (BF4-) anions. Spectroscopic studies are carried out near 2000 cm-1 for the C[Triple Bond]N stretching bands of NCS- and N(CN)2- as the IL anion as well as for NCS-, N(CN)2-, and azide (N3-) anions dissolved in [BM2IM][BF4]. The VER studies of N(CN)2- are reported for the first time. VER of N3-, NCS-, and N(CN)2- is measured in normal solvents, such as N-methylformamide, to compare with the IL solutions. The spectral shifts and VER rates of the anions in IL solution are quite similar to those in polar aprotic, conventional organic solvents, i.e., dimethylsulfoxide, and significantly different than those in methanol, in which there is hydrogen bonding. Similar studies were also carried out for the anions in another IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), in which the C2 hydrogen is present. The results for the anions are similar to those in the [BM2IM] containing ILs, in which the C2 hydrogen is methyl substituted. This suggests that substituting this hydrogen has, at most, a minor effect on the degree of hydrogen bonding in the anion-IL solvation interaction based on the infrared spectra and dynamics.

Vibrational spectroscopy and dynamics of small anions in ionic liquid solutions.

The solute−solvent interactions and the site−site distances between toluene and ionic liquids (ILs) 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [BMMIm][NTf2] and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIm][NTf2] at various molar ratios were determined by NMR experiments (1D NMR, rotating-frame Overhauser effect spectroscopy (ROESY)) and by molecular simulation using an atomistic force field. The difference in behavior of toluene in these ILs has been related to the presence of H-bonding between the C2−H and the anion in [BMIm][NTf2] generating a stronger association (>20 kJ·mol−1) than in the case of [BMMIm][NTf2]. Consequently, toluene cannot cleave this H-bond in [BMIm][NTf2] which remains in large aggregates of ionic pairs. However, toluene penetrates the less strongly bonded network of [BMMIm][NTf2] and interacts with [BMMIm] cations.

Interaction between the pi-System of Toluene and the Imidazolium Ring of Ionic Liquids: A Combined NMR and Molecular Simulation Study

Vibrational spectroscopic studies on ion solvation of lithium perchlorate in propylene carbonate + N,N-dimethylformamide mixtures.

1 H and 13 C NMR chemical shifts have been determined to investigate the interactions of acetone with room temperature ionic liquids ([C 4 mim][PF 6 ], [C 6 mim][PF 6 ], [C 8 mim][PF 6 ] and [C 6 mim][BF 4 ]) at various acetone mole fractions. Changes in the chemical shifts of hydrogen and carbon atoms of the above systems indicated that hydrogen bonds were formed between the ring protons, the methyl and methylene next to the nitrogen of the ionic liquids and the carbonyl oxygen of the acetone molecules. The strength of hydrogen bond was found to be influenced not only by the type of the anion but also by the length of alkyl chain on the imidazolium ring of cations. At the same time, ab initio calculations have been performed to support the NMR results.

A NMR study on the interactions of 1-alkyl-3-methylimidazolium ionic liquids with acetone

The infrared (IR) and Raman spectra of propylene carbonate (PC) containing various concentrations of LiClO4 have been measured and analyzed. The difference in spectra of PC with and without LiClO4 was attributed to the interaction of the PC molecules and lithium ions. This interaction occurs mainly on the carbonyl oxygen atom of the PC molecule. The ring deformation, symmetric ring deformation, carbonyl stretching and stretching of ring oxygens for PC are sensitive to this interaction. The solvation number of Li+ is also calculated. On the other hand, the structure of the ClO− 4 is also affected by PC molecule, forming the solvent separated ion pairs.

A Vibrational Spectroscopic Study of Ion Solvation in Lithium Perchlorate/Propylene Carbonate Electrolyte

Abstract 13C spin-lattice relaxation times of room temperature ionic liquids [C4mim][PF6], [C6mim][PF6], [C8mim][PF6],[C6mim][BF4] and [C6mim]Br in acetone-d6 have been determined at various acetone-d6 mole fractions. It was shown that the spin-lattice relaxation time increased with increasing acetone-d6 mole fractions, and was influenced not only by the type of the anions but also by the length of alkyl chain on the imidazolium cations. The results suggested that interactions between the cation and the anion of ionic liquids were weakened and the ionic motion of ionic liquids was enhanced with the addition of acetone-d6.

Junming Tang

Papers

Vibrational spectroscopic studies on ion solvation of lithium perchlorate in propylene carbonate + N,N-dimethylformamide mixtures.

A NMR study on the interactions of 1-alkyl-3-methylimidazolium ionic liquids with acetone

A Vibrational Spectroscopic Study of Ion Solvation in Lithium Perchlorate/Propylene Carbonate Electrolyte

A NMR Relaxation Study for the Interactions of some 1-alkyl-3-methylimidazolium Ionic Liquids with Acetone