Conversion Kinetics and Ionic Conductivity in Na-β"-Alumina + YSZ (Naβ"AY) Sodium Solid Electrolyte via Vapor Phase...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium-ion batteries are gaining traction for grid energy storage due to abundant resources and low cost.
• Na-β"-alumina is a highly conductive sodium ion conductor, but its mechanical strength and stability can be improved.
• Composite electrolytes offer enhanced properties compared to single-phase materials.

Purpose of the Study:

• To synthesize a Na-β"-Alumina + YSZ (Naβ"AY) composite sodium electrolyte via vapor phase synthesis.
• To investigate the conversion kinetics of α-Alumina within the composite.
• To determine the sodium ionic conductivity of the Naβ"AY composite electrolyte.

Main Methods:

• Vapor phase synthesis of Naβ"AY composite from α-Alumina and YSZ precursors.
• Heat treatment at 1250 °C to facilitate conversion, with measurements of weight and dimensions.
• Development of a weight-gain based model to analyze conversion kinetics.
• AC impedance spectroscopy to measure ionic conductivity at various temperatures.

Main Results:

• The conversion of α-Alumina to Naβ"AY was successfully achieved through coupled diffusion of sodium and oxygen ions.
• Effective diffusion coefficients for Na₂O (Deff) and interface transfer (keff) were estimated.
• The Naβ"AY composite exhibited high ionic conductivity: 1.3 × 10⁻¹ S cm⁻¹ at 300 °C and 1.6 × 10⁻³ S cm⁻¹ at 25 °C.
• A thin alumina coating improved oxygen diffusion estimation in single-phase Na-β"-alumina.

Conclusions:

• The synthesized Naβ"AY composite electrolyte demonstrates excellent mechanical strength and stability.
• The material shows promising ionic conductivity for applications in solid-state or molten salt sodium-ion batteries.
• This composite electrolyte is suitable for large-scale energy storage solutions, particularly for coupling with renewable energy sources.