Electron Delocalization Enables Sulfone-based Single-solvent Electrolyte for Lithium Metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-metal batteries (LMBs) offer high energy density but require stable electrolytes for both lithium metal anodes and high-voltage cathodes like LiNi_x Mn_y Co_1-x-y O₂ (NMC).
• Existing ether electrolytes are anode-stable but lack cathode stability, while sulfone electrolytes show good cathode stability but suffer from high viscosity and poor anode stability.
• Improving anode stability in NMC-compatible electrolytes is less explored than enhancing cathode stability in ether-based systems.

Purpose of the Study:

• To address the limitations of sulfone-based electrolytes, specifically high viscosity and poor anode stability, for practical lithium-metal battery applications.
• To design and synthesize a novel sulfone derivative that enhances both anode stability and electrolyte wetting properties.
• To demonstrate the electrochemical performance of the new electrolyte in LMBs under challenging cycling conditions.

Main Methods:

• Molecular modification of sulfone compounds using resonance and electron-withdrawing effects to tune properties.
• Introduction of additional oxygen and fluorination to reduce molecular viscosity and Lewis basicity.
• Electrolyte formulation using 2,2,2-trifluoroethyl mesylate (TFEM) as a single solvent.
• Electrochemical cycling of LMBs with NMC811 cathodes and lithium metal anodes at a low N/P ratio.

Main Results:

• The modified sulfone molecule, TFEM, exhibited significantly reduced viscosity and improved wetting capability compared to traditional sulfones.
• TFEM demonstrated enhanced anode stability, decreasing reactivity toward Li⁺ due to reduced Lewis basicity.
• LMBs utilizing TFEM as a single-solvent electrolyte achieved 90% capacity retention after 160 cycles at a C/3 discharge rate under harsh conditions (low N/P ratio).

Conclusions:

• Molecular engineering of sulfone electrolytes can effectively overcome limitations of viscosity and anode instability.
• TFEM represents a promising single-solvent electrolyte for stable and high-performance lithium-metal batteries.
• This work provides a new strategy for developing advanced electrolytes for next-generation energy storage systems.