Recent progress in understanding the solid electrolyte interphase of lithium and sodium metal anodes

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• The solid electrolyte interphase (SEI) is crucial for non-aqueous lithium- and sodium-metal battery (SMB) functionality.
• It prevents continuous electrolyte reduction, enabling reversible operation despite alkali metal instability.

Purpose of the Study:

• To review recent advancements in understanding SEI structure, formation, transport, and evolution on metal anodes.
• To highlight differences between lithium and sodium SEIs and discuss electrolyte engineering strategies.

Main Methods:

• Review of literature on SEI properties, including structure (two-layer model), formation mechanisms, and ion transport.
• Analysis of experimental observations like Tafel slopes and SEI-controlled kinetics.
• Evaluation of electrolyte engineering approaches for SEI improvement.

Main Results:

• The SEI features a dense inner inorganic layer for passivation and a porous outer layer for stress accommodation.
• Ion transport is primarily governed by grain boundaries and defects within the SEI.
• Sodium SEIs exhibit greater solubility, lower mechanical stability, and faster growth compared to lithium SEIs.

Conclusions:

• A deep mechanistic understanding of SEI formation and evolution is essential for creating durable, high-energy alkali-metal batteries.
• Electrolyte engineering strategies offer promising avenues for enhancing interfacial stability and battery longevity.