Cubic Iodide Li_x YI_3+x Superionic Conductors through Defect Manipulation for All-Solid-State Li Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Halide solid electrolytes (SEs) are crucial for advanced batteries due to their ionic conductivity and stability.
• Iodide SEs are less explored than chlorides or bromides, despite potential advantages like high ionic conductivity and anti-reduction stability.
• The Li sublattice softness and lower reduction limit in iodides offer unique opportunities for battery applications.

Purpose of the Study:

• To explore a new series of iodide SEs, specifically LiₓYI₃₊ₓ (x=2, 3, 4, 9).
• To investigate the structural properties and ionic conductivity of these novel iodide materials.
• To evaluate the electrochemical performance and Li-metal compatibility of the most promising candidate for solid-state batteries.

Main Methods:

• Synthesis and characterization of LiₓYI₃₊ₓ compounds.
• Synchrotron X-ray and neutron diffraction for structural analysis.
• Theoretical calculations to understand structure-property relationships.
• Electrochemical testing, including ionic conductivity measurements and all-solid-state Li-S battery performance.
• Interface molecular dynamics simulations to study Li-metal compatibility.

Main Results:

• A new series of high-symmetry cubic iodide SEs, LiₓYI₃₊ₓ, was successfully synthesized.
• These SEs exhibit abundant vacancies, which can be manipulated to optimize ionic conduction.
• Li₄YI₇ achieved an optimized ionic conductivity of 1.04 × 10⁻³ S/cm at 25°C.
• Li₄YI₇ demonstrated promising Li-metal compatibility, validated in all-solid-state Li-S batteries.

Conclusions:

• The study highlights the potential of iodide SEs, particularly those with high-symmetry cubic structures and engineered defects.
• Li₄YI₇ emerges as a promising solid electrolyte material for next-generation batteries.
• The findings provide valuable insights into the structure-ionic conduction relationship in halide SEs, encouraging further research in this area.