Structure and Conductivity in LISICON Analogues within the Li₄GeO₄-Li₂MoO₄ System.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Solid-state electrolytes are crucial for safer, high-energy lithium batteries, shifting focus from air-sensitive sulfides to stable oxides.
• LISICON-structured oxides like Li2+2xZn1-xGeO4 and Li3+xV1-xGexO4 are well-researched, but the Li4GeO4-Li2MoO4 system remains underexplored.

Purpose of the Study:

• To systematically investigate the Li4-2xGexMoxO4 solid solution, focusing on its solid solution limit, structural stability, local structure, and electrical properties.
• To explore a new class of air-stable, LISICON-type oxide solid electrolytes for advanced lithium battery applications.

Main Methods:

• Solid-state synthesis and characterization of the Li4-2xGexMoxO4 system.
• X-ray diffraction (XRD) and neutron diffraction for structural analysis and defect identification.
• Electrochemical impedance spectroscopy (EIS) to determine ionic conductivity.

Main Results:

• A γ-LISICON solid solution forms for 0.1 ≤ x < 0.4, distinct from the end members.
• A pure β-phase, β-Li3Ge0.5Mo0.5O4, is obtained at x = 0.5.
• Defect analysis of Li3.6Ge0.8Mo0.2O4 (x=0.2) reveals interstitial Li+ ions and defect clusters.
• The x = 0.2 composition exhibits the highest ionic conductivity: 1.11 × 10^-7 S cm^-1 at room temperature to 5.02 × 10^-3 S cm^-1 at 250 °C.

Conclusions:

• The Li4-2xGexMoxO4 system offers a promising route to novel, air-stable solid electrolytes.
• The identified defect structures in Li3.6Ge0.8Mo0.2O4 are key to its enhanced ionic conductivity.
• This research contributes to the development of safer and more efficient solid-state lithium batteries.