Revealing Solvent-Assisted Li⁺ Transport in the Solid Electrolyte Interphase operando

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• The solid electrolyte interphase (SEI) is crucial for lithium metal battery performance.
• Dynamic SEI evolution during cycling hinders accurate characterization.
• Understanding SEI properties is key to advancing energy-dense batteries.

Purpose of the Study:

• To investigate the real-time evolution of the SEI on lithium metal.
• To correlate SEI properties with battery performance in ether-based electrolytes.
• To elucidate the mechanism of Li+ transport within the SEI.

Main Methods:

• Dynamic electrochemical impedance spectroscopy (dEIS) applied to lithium metal.
• Operando characterization of SEI formation and evolution.
• Electrolyte variation with different degrees of fluorination.

Main Results:

• Faster stabilization of compact SEI resistance correlates with improved passivation and Coulombic efficiency.
• Compact SEI resistance is directly correlated with Li+ solvation energy.
• Evidence suggests a solvent-assisted Li+ transport mechanism within the SEI.

Conclusions:

• The SEI is not purely a solid-phase conductor; solvent presence is vital.
• Balancing SEI ionic conductivity and Li+ solvation is critical for battery performance.
• Findings challenge conventional SEI models and support a solvent-assisted transport mechanism.