Size induced structural changes in maricite-NaFePO₄: an in-depth study by experiment and simulations

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium ion batteries offer a cost-effective alternative for large-scale energy storage.
• Maricite-NaFePO4 is a promising cathode material due to its use of abundant elements.

Purpose of the Study:

• To investigate the crystallite size-dependent structural properties of maricite-NaFePO4.
• To understand the relationship between structure, bonding, and electrochemical performance.

Main Methods:

• X-ray diffraction (XRD) with Rietveld refinement.
• X-ray absorption spectroscopy (XAS) including oxygen K-edge analysis.
• First-principles density functional theory (DFT) calculations.

Main Results:

• Decreased crystallite size leads to reduced unit cell parameters and volume contraction.
• Changes in transition metal ion site symmetry and oxygen bonding character were observed with decreasing crystallite size.
• DFT calculations accurately predicted structural parameters, correlating volumetric changes with compressive strain and improved electronic diffusivity.

Conclusions:

• Crystallite size significantly impacts the structural and electronic properties of maricite-NaFePO4.
• Nano-crystalline maricite-NaFePO4 exhibits improved kinetics, making it a viable cathode material for sodium ion batteries.
• This research opens new avenues for developing efficient and affordable sodium ion battery technology.