Unveiling the Intercalation Mechanism in Fe

Area of Science:

• Materials Science
• Solid-state Chemistry
• Electrochemistry

Background:

• Monoclinic Fe2(MoO4)3 (FMO) displays distinct intercalation mechanisms for different guest ions.
• FMO undergoes a single-phase reaction with Na-ions but a two-phase reaction with Li-ions.
• Understanding these differences is limited by the lack of structural data for the fully sodiated phase, Na2Fe2(MoO4)3.

Purpose of the Study:

• To determine the crystal structure of Na2Fe2(MoO4)3.
• To elucidate the factors governing the different intercalation mechanisms of Na-ions and Li-ions in FMO.

Main Methods:

• Ab initio structure determination from powder diffraction data.
• Electrochemical characterization.
• Structural characterization.
• 3D bond valence sum difference map calculations.

Main Results:

• The crystal structure of Na2Fe2(MoO4)3 was solved and refined for the first time.
• Na insertion into FMO involves slight structural expansion, creating suitable sites for Na-ions and resulting in a single-phase reaction.
• Li insertion requires significant structural rearrangement of polyhedra to accommodate Li-ions, leading to a two-phase reaction.

Conclusions:

• The study successfully determined the Na2Fe2(MoO4)3 crystal structure.
• Differences in guest ion size and resulting structural adaptations dictate the single-phase (Na+) vs. two-phase (Li+) reaction mechanisms in FMO.
• Interatomic distances and coordination environments are key factors influencing intercalation behavior.