First-Principles Insights into Lithium-Rich Ternary Phosphide Superionic Conductors: Solid Electrolytes or Active...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Lithium-rich ternary phosphides are emerging as potential solid electrolytes (SEs) for solid-state batteries due to their high ionic conductivity.
• Their electrochemical and interfacial stability, crucial for battery performance, remain largely uncharacterized.

Purpose of the Study:

• To investigate the phase and electrochemical stability of phosphide-type SEs.
• To evaluate their suitability as solid electrolytes and potential as anode materials.

Main Methods:

• First-principles calculations were employed to study phase stability.
• Thermodynamic analysis was conducted to assess electrochemical stability.
• Lithium diffusion kinetics and storage capacity were also calculated.

Main Results:

• These SEs exhibit narrow electrochemical stability windows (< 0.5 V) and low anodic limits (~1 V vs Li/Li+).
• Electrochemical decomposition occurs due to oxidation, forming binary phosphorus compounds, especially at the cathode interface.
• Despite instability as electrolytes, efficient Li conduction with low energy barriers was observed.

Conclusions:

• The narrow electrochemical stability window suggests phosphide-type materials are likely unsuitable as solid electrolytes.
• Their decomposition products exhibit high lithium storage capacity (2547 mAh·g-1), indicating potential as high-rate anode materials.