Highly concentrated LiN(SO₂CF₃)₂/dinitrile electrolytes: Liquid structures, transport properties, and...

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Binary mixtures of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and dinitrile solvents (succinonitrile, glutaronitrile, adiponitrile) were investigated for their liquid structures, transport, and electrochemical properties.
• Stable crystalline solvates were formed in LiTFSA/SN and LiTFSA/ADN systems, while LiTFSA/GN mixtures exhibited glass-forming liquid behavior.

Purpose of the Study:

• To investigate the structural, transport, and electrochemical properties of LiTFSA-dinitrile solvent mixtures.
• To evaluate the potential of these electrolytes for electrochemical applications, particularly in lithium-sulfur batteries.

Main Methods:

• Raman spectroscopy was used to analyze the liquid structures and network formation in LiTFSA/GN mixtures.
• Pulsed field gradient NMR spectroscopy determined the self-diffusion coefficients of Li+ and TFSA- ions.
• Electrochemical measurements, including anion-blocking conditions and reductive stability tests, were performed.

Main Results:

• LiTFSA/GN mixtures formed glass-forming liquids with Li+-GN-Li+ network structures and significant ion pairing at higher concentrations.
• The Li+ transference number (tLi) reached 0.74 in a [LiTFSA]/[GN] = 1/1.5 electrolyte.
• Electrolytes showed increased reductive stability with higher LiTFSA concentration and were stable against Li metal electrodes under specific conditions.

Conclusions:

• The LiTFSA/GN system, particularly the [LiTFSA]/[GN] = 1/1.5 electrolyte, demonstrates promising properties for battery applications due to its high Li+ transference number.
• Despite low ionic conductivity, this electrolyte enabled high-rate discharge in a Li-S battery, highlighting its potential for advanced energy storage solutions.