Guideline of Dynamic Tunnel Structural Evolution for Durable Sodium-Ion Oxide Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Manganese-based oxide cathodes are promising for sodium-ion batteries (SIBs) due to cost and environmental benefits.
• Understanding structural evolution during element substitution is crucial for optimizing cathode performance.

Purpose of the Study:

• To investigate the impact of element substitutions on the structural evolution of tunnel-type Na0.44MnO2 cathodes.
• To elucidate the mechanisms behind structural transitions and their effect on sodium-ion transport and battery performance.

Main Methods:

• Systematic element substitution in Na0.44MnO2.
• Advanced scanning transmission electron microscopy (STEM) for structural analysis.
• Density functional theory (DFT) calculations for energy and structural stability.
• COMSOL simulations for stress accumulation and transport phenomena.

Main Results:

• Element substitutions alter the total energy, driving structural evolution from tunnel to other configurations.
• Direct observation of the tunnel-to-layered structure transition zone using STEM.
• DFT revealed Mg substitution uniquely forms layered/spinel heterostructures.
• Simulations showed enhanced Na+ transport and mitigated stress in the layered/spinel configuration.

Conclusions:

• Element substitutions provide design principles for dynamic tunnel structural evolution in Mn-based oxide cathodes.
• Mg-induced layered/spinel heterostructures improve interfacial integration, ion transport, and structural integrity.
• This work advances the design of high-performance sodium-ion batteries.