Surface molecular engineering to enable processing of sulfide solid electrolytes in humid ambient air

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Sulfide solid-state electrolytes (SSEs) offer high ionic conductivity and ductility for all-solid-state batteries (ASSBs).
• Moisture sensitivity of SSEs necessitates controlled environments, complicating manufacturing and increasing costs.
• Existing protection methods often compromise electrolyte performance or are incompatible with industrial processes.

Purpose of the Study:

• To develop a moisture-resilient surface modification for sulfide SSEs enabling ambient air processing.
• To investigate the chemical compatibility and protective mechanism of long-chain alkyl thiols on SSE surfaces.
• To demonstrate the practical application of modified SSEs in functional ASSBs.

Main Methods:

• Surface modification of Li₆PS₅Cl SSE with 1-undecanethiol.
• Exposure of modified SSEs to 33% relative humidity (RH) air for extended periods.
• Electrochemical impedance spectroscopy to measure ionic conductivity.
• X-ray diffraction (XRD) and other techniques to analyze structural integrity.
• Fabrication and testing of ASSBs utilizing the modified SSEs.

Main Results:

• 1-undecanethiol forms a stable protective layer on Li₆PS₅Cl, repelling moisture.
• Modified SSEs retained conductivity >1 mS cm^-1 for up to 2 days in 33% RH air, a >100-fold improvement in protection time.
• Negligible impact on ionic conductivity was observed.
• The modified SSE maintained function in a Li_0.5In|LiNi_0.8Co_0.1Mn_0.1O₂ ASSB after humidity exposure.
• Computational and experimental data confirmed the anchoring of thiol groups and hydrophobic protection.

Conclusions:

• Reversible surface modification with alkyl thiols enables practical, cost-effective manufacturing of sulfide SSEs under ambient conditions.
• This strategy significantly enhances the stability of SSEs against humidity, overcoming a major barrier for ASSB commercialization.
• The approach paves the way for scalable production of high-performance all-solid-state batteries.