High-concentration LiPF₆/sulfone electrolytes: structure, transport properties, and battery application

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Sulfone solvents offer non-flammability and oxidative stability, crucial for high-voltage Li batteries.
• Sulfolane-based high-concentration electrolytes (HCEs) demonstrate high Li+ ion transference numbers.
• The use of LiPF6 as a primary salt in sulfone-based HCEs remains largely unexplored.

Purpose of the Study:

• To investigate the phase behavior, solvate structures, and transport properties of LiPF6 in binary and ternary sulfone mixtures.
• To evaluate the potential of sulfone-based HCEs with LiPF6 for improved Li battery performance.

Main Methods:

• Systematic investigation of mixtures containing LiPF6 and sulfone solvents: sulfolane (SL), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), and 3-methyl sulfolane (MSL).
• Analysis of phase behaviors and solvate structures.
• Utilized Raman spectroscopy to study ion coordination and dissociation in ternary mixtures.

Main Results:

• Formation of stable crystalline solvates (Li(SL)4PF6 and Li(DMS)2.5PF6) in LiPF6/SL and LiPF6/DMS binary mixtures.
• LiPF6/EMS, LiPF6/MSL, and certain ternary mixtures remained liquid across a broad temperature range.
• In the HCE [LiPF6]/[SL]/[DMS] = 1/2/2, Li+ ions exhibited faster diffusion than PF6- due to ligand exchange, leading to a higher Li+ transference number.

Conclusions:

• Sulfone-based HCEs with LiPF6 are viable for Li batteries, with specific compositions showing enhanced Li+ transport.
• Competitive coordination of sulfone solvents to Li+ influences LiPF6 dissociation in ternary mixtures.
• The investigated HCEs offer potential for higher Li+ transference numbers compared to conventional electrolytes.