Li Dynamics in Mixed Ionic-Electronic Conducting Interlayer of All-Solid-State Li-metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium metal (Li ⁰ ) anodes offer high energy density for all-solid-state batteries (ASBs).
• Incompatibility between Li metal and sulfide solid-state electrolytes (SEs) hinders ASB development.
• Mixed ionic-electronic conductors (MIECs) are explored as interlayers to mitigate Li metal reactivity.

Purpose of the Study:

• To investigate lithium dynamics within a graphite interlayer, a common MIEC, during battery operation.
• To elucidate the mechano-chemo-electrochemical processes governing Li behavior at the Li-graphite|SE interface.
• To understand Li nucleation and transport pathways within the interlayer.

Main Methods:

• Utilized *operando* neutron imaging to visualize Li dynamics in real-time.
• Employed Raman spectroscopy to analyze the chemical and structural changes of the graphite interlayer.
• Performed computational modeling to determine Li nucleation barriers and transport paths.

Main Results:

• Cell assembly induced mechanochemical reactions, transforming graphite into a complex Li-graphite interlayer (SE, Li ⁰ , graphite intercalation compounds).
• During charging, Li ⁺ preferentially plated at the Li-graphite|SE interface, leading to Li ⁰ -dendrite formation and short circuits.
• Modeling identified the interface as the primary site for Li nucleation, dictating lithium transport.

Conclusions:

• The study reveals complex mechano-chemo-electrochemical processes within MIEC interlayers.
• Lithium ion and lithium metal behavior in interlayers is governed by competing factors.
• Understanding these processes is crucial for designing stable and efficient Li-metal ASBs.