Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO₂ Polymorphs as Cathode Materials for Na-Ion...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Sodium iron dioxide (NaFeO2) is a promising metal-free cathode material for sodium-ion batteries.
• Understanding defects and doping is crucial for optimizing NaFeO2 performance.

Purpose of the Study:

• Investigate defects, sodium diffusion, and cation doping in α- and β-NaFeO2 polymorphs.
• Evaluate the impact of various dopants on NaFeO2 properties.
• Identify strategies for enhancing sodium-ion transport.

Main Methods:

• Classical potential simulations to study defects and diffusion.
• Examination of aliovalent and isovalent dopants.
• Density Functional Theory (DFT) for electronic structure calculations.

Main Results:

• Identified Na Frenkel and cation antisite as favorable defects.
• Observed distinct sodium diffusion paths in α- and β-NaFeO2 polymorphs.
• Determined energetically favorable doping strategies using Co, Zn, Si, and Ge to control Na vacancy and interstitial concentrations.
• DFT revealed that favorable dopants reduce the band gap.

Conclusions:

• Defect engineering and targeted doping can significantly enhance sodium diffusion in NaFeO2.
• Subvalent doping increases interstitial Na, while Si/Ge doping creates Na vacancies for improved diffusion.
• Optimized NaFeO2 through doping offers a pathway for advanced sodium-ion battery cathodes.