An insight into intrinsic interfacial properties between Li metals and Li₁₀GeP₂S₁₂ solid electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Computational Materials Science

Background:

• All-solid-state batteries (ASSBs) require stable interfaces between lithium metal anodes and solid electrolytes.
• Li$_{10}$GeP$_{2}$S$_{12}$ (LGPS) is a promising solid electrolyte, but its interface with lithium metal needs thorough investigation.
• Understanding interfacial properties is crucial for mitigating issues like high interfacial resistance and ensuring battery longevity.

Purpose of the Study:

• To investigate the interfacial properties and lithium ion migration kinetics between lithium metal and the LGPS[001] surface.
• To elucidate the electronic structure and stability of different LGPS surface terminations (PS$_{4}$ and GeS$_{4}$).
• To reveal the equilibrium interfacial structures and predict the formation of solid electrolyte interphases (SEI).

Main Methods:

• Density functional theory (DFT) simulations were employed to study surface electronic structure, structural relaxation, and adhesion energies.
• Experimental electrochemical impedance spectroscopy (EIS) was used to verify interfacial resistance in Li/LGPS/Li cells.
• Simulations of lithium ion migration kinetics across the interfaces were performed to determine energy barriers.

Main Results:

• Both PS$_{4}$- and GeS$_{4}$-terminated LGPS[001] surfaces showed reduced electrochemical stability.
• SEI formation was predicted at both Li/PS$_{4}$-LGPS and Li/GeS$_{4}$-LGPS interfaces, leading to high interfacial resistance.
• Lower energy barriers for Li$^{+}$ migration were observed at the Li/GeS$_{4}$-LGPS interface compared to Li/PS$_{4}$-LGPS, suggesting potential for Ge-rich phase formation.

Conclusions:

• The Li/LGPS interface exhibits inherent instability and significant resistance due to SEI formation.
• The GeS$_{4}$-terminated interface offers a more favorable pathway for lithium ion migration, potentially improvable through Ge-rich phase engineering.
• This study provides critical insights into Li/LGPS interfacial behavior, essential for designing advanced all-solid-state batteries.