Li₂GeS₃: Lithium Ionic Conductor with an Unprecedented Structural Type.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Lithium-ion batteries (LIBs) face safety challenges due to flammable liquid electrolytes.
• All-solid-state batteries (ASSBs) offer enhanced safety by employing solid electrolytes.
• The crystal structure of Li₂GeS₃, a potential solid electrolyte, remained poorly understood since its initial report.

Purpose of the Study:

• To elucidate the detailed crystal structure of Li₂GeS₃.
• To investigate the ionic conductivity and lithium diffusion pathways in Li₂GeS₃.
• To assess the potential of Li₂GeS₃ as an ionic conductor for ASSBs.

Main Methods:

• Synthesis of Li₂GeS₃ via solid-state reaction of Li₂S and GeS₂.
• Ab initio structure determination using powder X-ray and time-of-flight neutron diffraction data.
• Measurement of ionic conductivity at various temperatures.
• Bond valence energy landscape calculations for diffusion pathway analysis.

Main Results:

• Discovery of a novel hexagonal crystal structure (space group *P*6₁ ) for Li₂GeS₃.
• The structure features a distorted hexagonal close-packed arrangement of sulfur anions with Li and Ge in tetrahedral sites.
• Measured ionic conductivity values ranged from 1.63 × 10⁻⁸ S cm⁻¹ at 303 K to 2.45 × 10⁻⁷ S cm⁻¹ at 383 K.
• Calculations revealed three-dimensional lithium diffusion pathways.

Conclusions:

• The unveiled crystal structure of Li₂GeS₃ provides fundamental insights into its ionic conduction properties.
• Li₂GeS₃ exhibits potential as an ionic conductor for all-solid-state batteries.
• This novel structure offers opportunities for developing advanced ionic conductors through chemical modifications.