NaMgX₃ (X = Cl, Br) for solid electrolyte interphases: atomistic insights into defects, surfaces and doping...

Area of Science:

• Materials Science
• Computational Chemistry
• Electrochemistry

Background:

• Advancements in metal-ion batteries require solid electrolyte interphases (SEI) with tailored defect chemistry and mechanical properties.
• Understanding the fundamental properties of potential SEI materials is crucial for battery performance and longevity.

Purpose of the Study:

• To quantitatively compare the properties of NaMgCl3 and NaMgBr3 using atomistic simulations for SEI design.
• To evaluate their electronic, mechanical, and ionic transport characteristics relevant to battery applications.

Main Methods:

• Atomistic simulations were employed to investigate the electronic band gaps, mechanical stability, and defect chemistry of NaMgCl3 and NaMgBr3.
• Calculations focused on Schottky and Frenkel disorder, aliovalent substitution effects, and ionic conductivity.
• Surface energetics and facet-dependent properties were analyzed to understand surface behavior.

Main Results:

• Both NaMgCl3 (5.0 eV) and NaMgBr3 (3.7 eV) exhibit wide band gaps, indicating electronic insulation and mechanical stability suitable for SEI.
• Bromide substitution in NaMgBr3 expands the lattice, softens the framework, and significantly enhances ionic conductivity (Ea ~0.41 eV, conductivity ~2.1 × 10^-6 S cm^-1) compared to NaMgCl3.
• Defect chemistry is influenced by Na-X Schottky, Na+/Li+ Frenkel disorder, and aliovalent substitution, with divalent dopants being practical Na+ vacancy sources.
• Facet-dependent surface energetics show high-energy facets (e.g., (100)) exhibit lower activation barriers for ion transport, suggesting potential for engineered conductive SEI formation.

Conclusions:

• NaMgCl3 and NaMgBr3 are promising candidates for solid electrolyte interphases in metal-ion batteries.
• Bromide substitution is a key strategy for enhancing ionic conductivity and mechanical deformability.
• Facet engineering and controlled doping offer routes to optimize SEI performance and achieve defect-driven conductivity.