Solid-Gas Interphase Formation in Anode-Free Solid-State Batteries

Area of Science:

• Battery Technology
• Materials Science
• Electrochemistry

Background:

• The solid electrolyte interphase (SEI) is crucial for battery performance.
• Highly reactive components like Li metal anodes face additional interfacial stability challenges.
• Solid-state batteries (SSBs) present a unique solid-gas interface distinct from liquid electrolyte systems.

Purpose of the Study:

• To investigate the dynamic formation of a solid-gas interphase (SGI) on Li metal anodes in SSBs.
• To understand the factors influencing SGI formation and its impact on battery performance.
• To differentiate SGI from the conventional SEI layer.

Main Methods:

• Fabrication of a customized environmental chamber for controlled gas composition and pressure.
• Cycling of SSBs under stack pressure with controlled Li metal anode exposure.
• Operando X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum to study dynamic SGI formation.
• Assembly of solid-state pouch cells in a dry room environment.

Main Results:

• SGI formation is dependent on plated Li capacity, ambient gas composition, and aging time.
• SGI formation directly impacts the Coulombic efficiency of the battery.
• Operando XPS revealed dynamic SGI formation even with trace background reactant gases.
• SGI formation influences the calendar life of practical SSB configurations.

Conclusions:

• The solid-gas interphase (SGI) is a critical factor in the stability and performance of Li metal anodes in SSBs.
• Understanding and controlling SGI formation is essential for advancing SSB technology.
• SGI represents a distinct interfacial phenomenon compared to the SEI layer.