A Low-Cost Liquid-Phase Method of Synthesizing High-Performance Li₆PS₅Cl Solid-Electrolyte

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Lithium sulfide (Li2S) is a key but costly raw material for Li6PS5Cl solid-electrolytes.
• Current production methods for Li6PS5Cl face challenges in cost, scalability, and performance.
• All-solid-state lithium batteries require high-performance, cost-effective solid-electrolytes for practical application.

Purpose of the Study:

• To develop an economically viable and scalable synthesis method for high-performance Li6PS5Cl.
• To circumvent the need for commercial lithium sulfide (Li2S) in the synthesis process.
• To reduce the overall material cost of Li6PS5Cl for practical battery development.

Main Methods:

• A novel "de novo liquid phase method" was employed for Li6PS5Cl synthesis.
• In situ generation of Li2S from inexpensive lithium chloride (LiCl) and sodium sulfide.
• A consecutive process allowing LiCl addition at the start without intermediate separation.

Main Results:

• Achieved a material cost of approximately $55/kg for Li6PS5Cl, nearing the practical target of $50/kg.
• Synthesized Li6PS5Cl exhibits high ionic conductivity (∼2 mS/cm).
• Demonstrated outstanding cyclability with >99.8% capacity retention over 400 cycles in full battery tests.

Conclusions:

• The "de novo liquid phase method" offers a cost-effective and scalable route to high-performance Li6PS5Cl.
• This method addresses the limitations of using commercial Li2S, paving the way for practical solid-state batteries.
• The developed Li6PS5Cl shows significant potential for advancing sulfide-based solid-electrolyte technology.