Disorder-Mediated Ionic Conductivity in Irreducible Solid Electrolytes.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Solid-state batteries offer higher energy density than lithium-ion batteries, especially with advanced anodes like lithium metal or silicon.
• Current solid electrolytes often decompose at low voltages required by these anodes, causing lithium loss and increased resistance.
• Developing thermodynamically stable electrolytes at low operating voltages is crucial for preventing performance degradation.

Purpose of the Study:

• To discover and characterize a new family of irreducible solid electrolytes.
• To investigate the mechanism behind enhanced ionic conductivity in these novel materials.
• To provide a theoretical framework for understanding disordered ion conductors.

Main Methods:

• Mechanochemical synthesis by dissolving lithium nitride into the Li2S antifluorite structure.
• Synthesis of crystalline Li2+xS1-xNx phases.
• Ionic conductivity measurements using impedance spectroscopy.
• First-principles density functional theory (DFT) calculations.
• Percolation analysis with environment-specific activation energies.

Main Results:

• Discovery of highly conducting crystalline Li2+xS1-xNx phases with conductivity >0.2 mS cm-1 at room temperature.
• Demonstration that anion sublattice disordering in Li2+xS1-xNx boosts ionic conductivity by up to 10^5 compared to Li2S.
• Development of a theoretical framework to explain conductivity enhancement in disordered ion conductors.
• Rationalization of how increasing nitrogen content improves conductivity and lowers activation energy.

Conclusions:

• The new Li2+xS1-xNx solid electrolytes are stable at low anode operating voltages, preventing decomposition.
• The findings offer a pathway to understanding and designing advanced disordered solid electrolytes.
• This work addresses key challenges in solid-state battery performance, particularly anode-side stability.