Enhancing the Lithium Ion Conductivity in Lithium Superionic Conductor (LISICON) Solid Electrolytes through a Mixed...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Lithium superionic conductor (LISICON)-related compositions, specifically Li₄±ₓSi₁₋ₓXₓO₄ (where X = P, Al, or Ge), are critical materials investigated as solid electrolytes.
• All-solid-state batteries require advanced solid electrolytes with high ionic conductivity for improved safety and performance.

Purpose of the Study:

• To significantly enhance room-temperature lithium ion conductivity in LISICON-related materials.
• To investigate the effects of substituting silicon sites with various elements (P, Al, Ge) on ionic transport properties.
• To elucidate the lithium-ion diffusion mechanisms within these substituted materials.

Main Methods:

• Employed a combined approach of computer simulations and experimental analysis.
• Synthesized and characterized a range of doped LISICON compositions, including Li₄SiO₄, Li₃.₇₅Si₀.₇₅P₀.₂₅O₄, Li₄.₂₅Si₀.₇₅Al₀.₂₅O₄, Li₄Al₀.₃₃Si₀.₃₃P₀.₃₃O₄, and Li₄Al₁/₃Si₁/₆Ge₁/₆P₁/₃O₄.
• Analyzed lithium-ion diffusion mechanisms at different temperatures.

Main Results:

• Achieved improvements in lithium ion conductivity by several orders of magnitude through silicon site substitution.
• Observed three distinct Li⁺ ion diffusion mechanisms dependent on temperature.
• Demonstrated that polyanion mixing from substitution lowers the transition temperature to a superionic state.

Conclusions:

• Substitution on silicon sites is an effective strategy for enhancing lithium ion conductivity in LISICON-related materials.
• The observed diffusion mechanisms and the effect of polyanion mixing provide a rational basis for conductivity enhancement.
• These findings offer valuable insights for designing next-generation solid electrolytes for all-solid-state batteries.