Ionic conduction in ammonia functionalised closo-dodecaborates MB₁₂H₁₁NH₃ (M = Li and Na)

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Metal hydroborates are explored for solid-state ion conductors in batteries due to favorable properties.
• Limited research exists on hydroborates as solid-state electrolytes.

Purpose of the Study:

• To synthesize and evaluate MB₁₂H₁₁NH₃ (M = Li, Na) hydroborates as electrolyte materials for all-solid-state batteries.
• To investigate the structural and ionic conductivity properties of these novel hydroborates.

Main Methods:

• Synthesis of LiB₁₂H₁₁NH₃ and NaB₁₂H₁₁NH₃.
• X-ray diffraction for structural analysis of NaB₁₂H₁₁NH₃, including solving the room temperature polymorph.
• Ionic conductivity measurements at elevated temperatures.

Main Results:

• The room temperature structure of α-NaB₁₂H₁₁NH₃ was determined (space group P2₁2₁2₁).
• A polymorphic transition to cubic Fm3̄m was observed near 140 °C for NaB₁₂H₁₁NH₃.
• LiB₁₂H₁₁NH₃ and NaB₁₂H₁₁NH₃ exhibited cationic conductivities of 3.0 × 10^-4 S cm^-1 and 1.2 × 10^-4 S cm^-1 at 200 °C, respectively.
• Ionic conductivity improved with hydration.

Conclusions:

• MB₁₂H₁₁NH₃ (M = Li, Na) are viable candidates for solid-state electrolytes.
• The bulky -NH₃ group may limit re-orientational dynamics and thus ionic conductivity.
• Further research could focus on structural modifications to enhance conductivity.