Coordination-Disorder Engineering of Amorphous Halide Superionic Conductors for Long-Cycle All-Solid-State Sodium...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium superionic conductors are key for advanced sodium-ion batteries, improving energy density and safety.
• Conventional crystalline sodium-halide electrolytes offer stability but are limited by vacancy-mediated transport.
• Ordered crystalline frameworks restrict ionic conductivity in current sodium-ion battery electrolytes.

Purpose of the Study:

• To engineer amorphous chloride conductors for enhanced ionic conductivity in sodium-ion batteries.
• To overcome the limitations of vacancy-mediated transport in crystalline sodium superionic conductors.
• To develop safer and higher-energy-density sodium-ion battery electrolytes.

Main Methods:

• Cation engineering strategy to induce structural coordination disorder.
• Synthesis of amorphous chloride conductors with general formulas A_2-xM_1-xTa_xCl₆ and NaNb_1-xTa_xCl₆.
• Electrochemical characterization, including ionic conductivity measurements and stability testing.
• Fabrication and testing of all-solid-state sodium cells.

Main Results:

• Achieved ionic conductivities exceeding 10^-3 S cm^-1 at ambient conditions.
• Optimized Na_1.4Zr_0.4Ta_0.6Cl₆ composition showed a room-temperature conductivity of 1.95 × 10^-3 S cm^-1.
• Demonstrated enhanced oxidative stability (>4.0 V) and mechanical robustness due to disordered structure.
• All-solid-state sodium cells exhibited good rate performance and long-cycling stability (86% after 1000 cycles).

Conclusions:

• Amorphous-phase engineering via cation substitution is a viable strategy for designing superior sodium superionic conductors.
• Disordered amorphous structures overcome limitations of crystalline frameworks, enabling higher ionic conductivity.
• These novel electrolytes represent a transformative approach for next-generation sodium-ion batteries.