Conductivity-Viscosity Decoupling in Concentrated LiTFSI and LiCl Electrolytes

Area of Science:

• Electrochemistry
• Materials Science

Background:

• Water-in-salt (WiS) electrolytes offer superior electrochemical stability for energy storage.
• Understanding ion transport mechanisms in WiS electrolytes is crucial for performance optimization.
• Decoupling behavior in halogen-inorganic anion WiS electrolytes is less understood than in organic anion systems.

Purpose of the Study:

• To investigate and compare the conductivity-viscosity decoupling mechanisms in concentrated LiTFSI and LiCl electrolytes.
• To elucidate the structural and dynamic differences influencing ion transport in these WiS electrolytes.
• To provide insights into the conduction mechanism of LiCl-based WiS electrolytes for improved battery and supercapacitor design.

Main Methods:

• Comparative analysis of conductivity and viscosity measurements.
• Structural analysis using techniques like X-ray diffraction (XRD) or similar.
• Molecular dynamics (MD) simulations to probe ion dynamics and interactions.

Main Results:

• Distinct conductivity-viscosity decoupling behaviors were observed: α < 1 for LiTFSI and α > 1 for LiCl.
• Concentrated LiTFSI electrolytes showed ordered structures around 6 Å and 13 Å, absent in LiCl electrolytes.
• MD simulations revealed decoupling in LiTFSI arises from TFSI⁻ nanocluster counteraction, while LiCl decoupling stems from Li⁺-Cl⁻ pair cooperative motion.

Conclusions:

• Significant differences exist in ion transport mechanisms between LiTFSI and LiCl WiS electrolytes.
• The findings clarify the conduction pathways in LiCl-based WiS electrolytes.
• This research guides the rational design of advanced electrolytes for high-performance energy storage devices.