Defect Enabled Room Temperature Superionicity in 3D Covalent Mixed Ionic Electronic Conductor LiB₃

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Mixed ionic-electronic conductors (MIECs) are crucial for energy applications but often suffer from low ionic conductivity and limited operating temperatures.
• Developing intrinsic MIECs with enhanced transport properties and stability is a key challenge in materials science.

Purpose of the Study:

• To investigate the ionic diffusion and coupled transport properties of LiB3 using first-principles calculations and machine learning molecular dynamics (MLMD).
• To explore the potential of LiB3 as a high-performance material for solid-state energy storage applications.

Main Methods:

• First-principles calculations were employed to understand fundamental material properties.
• Machine learning molecular dynamics (MLMD) simulations were used to explore ionic diffusion and transport over a wide temperature range.
• Defect engineering, specifically introducing vacancies, was utilized to modulate material properties.

Main Results:

• LiB3 exhibits a superionic state at 800 K with high ionic conductivity (0.254 S/cm) and excellent electronic conductivity (10^3-10^4 S/cm).
• The material demonstrates remarkable structural stability, with only 2.93% volume expansion from 0-800 K.
• Introducing 6.25% vacancies reduced the superionic transition temperature to 300 K while maintaining high ionic conductivity (0.249 S/cm).

Conclusions:

• LiB3 is identified as an intrinsic MIEC material with a unique combination of fast ionic and high electronic conductivity.
• The material's stability and tunable properties through defect engineering highlight its significant potential for advanced solid-state energy storage systems.