An Iodide-Chloride Solid Electrolyte Compatible with Lithium Metal for All-Solid-State Lithium Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Halide superionic conductors offer high ionic conductivity and mechanical flexibility.
• Interfacial instability with lithium metal anodes limits halide-based all-solid-state lithium-metal batteries (ASSLBs).

Purpose of the Study:

• To synthesize novel iodide-chloride solid electrolytes, Li₂ZrCl_6-xI_x (x = 0-3).
• To enhance the electrochemical stability of halide electrolytes against lithium metal anodes.

Main Methods:

• Solid-state synthesis of Li₂ZrCl_6-xI_x electrolytes.
• Electrochemical testing of symmetric and full cells.
• Surface characterization using X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

Main Results:

• Li₂ZrCl₄I₂ demonstrated stable cycling (>6000 h) in Li/Li₂ZrCl₄I₂/Li symmetric cells at 0.2 mA cm^-2.
• High critical current densities up to 6 mA cm^-2 were achieved.
• Full cells with Li₂ZrCl₄I₂ showed improved cycling stability and capacity retention.
• XPS and ToF-SIMS confirmed the formation of a LiI/LiCl passivation layer, stabilizing the Li metal anode.

Conclusions:

• Iodide substitution in halide electrolytes enhances reduction stability by promoting covalent bonding.
• The LiI/LiCl interfacial layer effectively suppresses electrolyte decomposition and stabilizes the lithium metal anode.
• These findings present a viable strategy for developing robust halide electrolytes for high-energy-density ASSLBs.