Highly Conductive Irreducible Electrolytes for Next-Generation Low-Potential Anodes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• All-solid-state batteries offer enhanced safety and energy density over conventional lithium-ion batteries.
• Solid electrolytes are crucial for enabling high-energy anodes like metallic lithium and silicon.
• Current solid electrolytes often suffer from reductive decomposition at low potentials due to high-valence cations, causing lithium loss.

Purpose of the Study:

• To develop novel solid electrolytes that are thermodynamically stable at low potentials, possess high ionic conductivity, and offer sufficient oxidative stability.
• To investigate a new family of Li-rich antifluorite irreducible solid electrolytes, specifically Li_2.65S_0.35N_xP_0.65-x, for all-solid-state battery applications.
• To evaluate the compatibility and performance of these electrolytes with silicon anodes.

Main Methods:

• Synthesis and characterization of a new series of nitrido-phosphido-sulfide solid electrolytes (Li_2.65S_0.35N_xP_0.65-x).
• Measurement of ionic conductivity and oxidative stability of the optimized electrolyte composition.
• Computational simulations including *ab initio* molecular dynamics and density functional theory to understand Li diffusion mechanisms.
• Fabrication and testing of a full battery cell utilizing the novel solid electrolyte with a silicon anode and a LiCoO₂-Li₃InCl₆ cathode.

Main Results:

• The optimized composition, Li_2.65S_0.35N_0.15P_0.5, achieved a high ionic conductivity of 1.05 mS cm^-1 and oxidative stability of 1.15 V vs Li⁺/Li.
• Computational studies revealed that enhanced Li diffusion is attributed to enlarged diffusion bottleneck sizes resulting from anion substitution.
• The solid electrolyte demonstrated excellent compatibility with silicon anodes, enabling a high initial Coulombic efficiency of 94.2% and stable cycling performance in a full cell.

Conclusions:

• Li-rich antifluorite irreducible solid electrolytes, particularly nitrido-phosphido-sulfides, are promising candidates for next-generation all-solid-state batteries.
• The developed electrolyte overcomes the limitations of reductive decomposition at low potentials, facilitating the use of high-energy-density anodes.
• This research highlights the potential of irreducible solid electrolytes in designing safer and more efficient all-solid-state batteries.