Compositional flexibility in irreducible antifluorite electrolytes for next-generation battery anodes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Solid-state batteries offer higher energy density potential than lithium-ion batteries, especially with next-generation anodes like lithium metal or silicon.
• A major challenge is finding solid electrolytes with high ionic conductivity and stability against highly reducing anode potentials.
• Irreducible electrolytes, utilizing non-decomposable anions, present a promising strategy to prevent electrolyte decomposition.

Purpose of the Study:

• To explore the compositional flexibility of disordered antifluorite frameworks for discovering new irreducible solid electrolytes.
• To understand the conductivity enhancement in Li-rich antifluorite phases.
• To investigate the synthesis and conductivity of halogen-substituted analogues for improved performance.

Main Methods:

• Mechanochemical synthesis was employed to create disordered antifluorite materials.
• Density functional theory (DFT) calculations were used to analyze ionic conductivity origins.
• Compositional tuning through substitution (S, Br) was performed to enhance properties.

Main Results:

• A solid solution of Li-deficient antifluorite phases, Li_{1+2x}Cl_{1-x}N_x (0.33 < x < 0.5), was identified, encompassing Li9N2Cl3 and Li5NCl2.
• DFT calculations revealed a 5-order-of-magnitude increase in ionic conductivity compared to rock-salt LiCl.
• Halogen substitution (S, Br) led to a 10-fold conductivity increase, reaching 0.2 mS cm^-1 for Li2.31S0.41Br0.14N0.45.

Conclusions:

• Irreducible antifluorite-like phases exhibit significant compositional modifiability.
• This work opens avenues for discovering new compositions with enhanced conductivity.
• The findings contribute to overcoming solid-electrolyte decomposition and lithium loss issues in advanced batteries.