Visualizing the failure of solid electrolyte under GPa-level interface stress induced by lithium eruption

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Solid electrolytes are key for high-performance lithium metal batteries.
• Li-filament penetration remains a critical failure mechanism, hindering battery safety and lifespan.
• The electrochemo-mechanical failure mechanisms at the Li|solid electrolyte interface are not fully understood.

Purpose of the Study:

• To elucidate the Li deposition dynamics and failure mechanisms at the Li|Li7La3Zr2O12 (LLZO) interface.
• To investigate the impact of mechanical constraints and charging rates on Li deposition behavior.
• To identify strategies for mitigating crack initiation and improving the rate capability of solid electrolytes.

Main Methods:

• In situ transmission electron microscopy (TEM) to visualize Li|LLZO interface evolution.
• Controlled mechanical constraints and charging rates during Li deposition.
• Analysis of stress generation and crack propagation at the nanoscale.

Main Results:

• Under high constraint and low rates, Li deposition causes lateral expansion and stress buildup, leading to LLZO cracking upon eruption.
• Rapidly built-up local stress (GPa level) can fracture defect-free single-crystal LLZO.
• Weaker mechanical constraints promote vertical Li growth, enabling high current densities (A·cm⁻²) without LLZO damage.

Conclusions:

• Crack initiation at the Li|LLZO interface is governed by local current density, mass transport, and stress dissipation mechanisms.
• Optimizing mechanical constraints and interface design is crucial for preventing failure.
• Strategies for fast Li transport and stress relaxation can enhance the rate capability of solid electrolytes for advanced batteries.