Structures and conductivities of stable and metastable Li₅GaS₄ solid electrolytes

Area of Science:

• Solid-state chemistry
• Materials science
• Electrochemistry

Background:

• Ionic conductivity in solid electrolytes is critical for energy storage applications.
• Understanding structure-property relationships in solid electrolytes is key to enhancing performance.
• Metastable phases often exhibit superior ionic conductivity compared to stable phases.

Purpose of the Study:

• To synthesize and characterize metastable and stable phases of lithium thiogallate (Li5GaS4).
• To investigate the structural differences and defects influencing ionic conductivity.
• To correlate crystal structure with ionic conductivity in Li5GaS4.

Main Methods:

• Mechanochemical synthesis of metastable Li5GaS4.
• Thermal treatment to obtain the stable Li5GaS4 phase.
• X-ray diffraction and conductivity measurements.

Main Results:

• Metastable Li5GaS4 possesses an antifluorite-type structure with significant cationic disorder.
• Stable Li5GaS4 adopts a monoclinic structure, analogous to Li5AlS4.
• The metastable phase exhibits an ionic conductivity of 2.1 × 10^-5 S cm^-1 at 25 °C, 1000 times higher than the stable phase.

Conclusions:

• Cation disorder in the metastable antifluorite structure of Li5GaS4 is responsible for its enhanced ionic conductivity.
• The structural differences between metastable and stable phases significantly impact ionic transport.
• This study provides insights into designing high-conductivity solid electrolytes.