Interfacial Energy Engineering via Fluorine Doping Suppresses Lithium Self-Permeation in Li₃N Solid Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Non-electrochemical lithium permeation is a critical failure mode in all-solid-state lithium metal batteries (ASSLMBs).
• Lithium (Li) self-permeation in Li3N solid-state electrolytes (SSEs) under pressure and heat degrades interfacial stability.
• This permeation forms mixed conductive regions, compromising battery function.

Purpose of the Study:

• To investigate and mitigate lithium self-permeation in Li3N SSEs.
• To develop a strategy for enhancing interfacial stability in ASSLMBs.
• To improve the safety and cycle life of lithium metal batteries.

Main Methods:

• Developed an anion-tuning strategy by doping Li3N with LiF to create Li2.9N0.95F0.05.
• Investigated the effect of fluorine substitution on interfacial energy between Li and SSE.
• Fabricated and tested Li-symmetric cells and ASSLMBs with Li2.9N0.95F0.05 as SSE interlayers.

Main Results:

• Fluorine substitution effectively suppressed spontaneous Li permeation by elevating interfacial energy.
• Li2.9N0.95F0.05 exhibited high ionic conductivity (5.8 × 10^-4 S cm^-1) and low activation energy (0.326 eV).
• Li-symmetric cells achieved stable cycling (>1000 h), and ASSLMBs retained 80% capacity after 120 cycles.

Conclusions:

• Anion tuning via LiF doping is an effective strategy to stabilize Li metal interfaces in ASSLMBs.
• The developed Li2.9N0.95F0.05 SSE demonstrates significant potential for engineering viable and high-performance ASSLMBs.
• This work provides a pathway to advance the safety and reliability of next-generation lithium metal batteries.