Interphase Engineering via Solvent Molecule Chemistry for Stable Lithium Metal Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Lithium metal batteries offer high energy density but face anode stability challenges.
• Electrolyte composition and solvation structure critically influence lithium metal battery performance.
• Side reactions and dendrite formation hinder the practical application of lithium metal anodes.

Purpose of the Study:

• To synthesize novel fluorinated ethers with weak-solvation properties for lithium metal batteries.
• To investigate the impact of molecular design on electrolyte solvation structure and electrochemical performance.
• To demonstrate the efficacy of these electrolytes in high-energy density lithium metal batteries, including lithium-sulfur systems.

Main Methods:

• Synthesis of fluorinated ethers with specific molecular structures (longer carbon chains, methine groups).
• Electrolyte characterization focusing on solvation structure (e.g., aggregation number).
• Electrochemical testing of lithium metal batteries and lithium-sulfur batteries under various temperature conditions.
• Pouch cell fabrication and performance evaluation (energy density, cycle life).

Main Results:

• Synthesized fluorinated ethers exhibited weak-solvation ability due to steric effects.
• Electrolytes with high aggregation number (97.96%) achieved high Coulombic efficiency (CE) of 99.71% at 25°C and 98.56% at -20°C.
• Lithium-sulfur batteries showed excellent performance from -20°C to 50°C with a LiF/LiO2-rich interphase.
• Pouch cells achieved an energy density of 344.4 Wh/kg with 80% capacity retention after 50 cycles.

Conclusions:

• Novel solvent design using molecular chemistry is a viable strategy for optimizing solvation structures.
• Weak-solvating fluorinated ether electrolytes significantly improve lithium metal anode stability and battery performance.
• This approach enables high-energy density lithium metal batteries with enhanced operational temperature ranges and cycle life.