Probing Phase Formation and Structural Transformations in Sodium Extraction and Insertion of NaFe_1-MnPO₄ through...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Manganese (Mn) substitution enhances energy density in iron (Fe)-based electrode materials due to its higher redox potential.
• Excessive Mn content can negatively impact electrochemical performance, leading to capacity loss and increased voltage hysteresis.
• Optimal composition NaFe_0.8Mn_0.2PO₄ shows enhanced performance over NaFePO₄.

Purpose of the Study:

• Investigate phase stability upon desodiation in Mn-poor and Mn-rich NaFe_1-MnPO₄ compositions using density functional theory (DFT).
• Understand the influence of Na-vacancies and charge ordering on phase stability in antagonistic systems.
• Identify key parameters for designing high-performance electrode materials.

Main Methods:

• Density functional theory (DFT) calculations.
• Analysis of phase stability in NaFe_0.75Mn_0.25PO₄ and NaFe_0.25Mn_0.75PO₄ systems.
• Investigation of desodiation pathways and intermediate phases.

Main Results:

• Distinct phase stability behaviors were observed in Mn-poor and Mn-rich compositions.
• Na-vacancy formation and charge ordering significantly influence phase stability.
• The number of intermediate phases during desodiation is critical for buffering volume changes.

Conclusions:

• Light manganese substitution in iron phosphate electrode materials is crucial for superior electrochemical performance.
• Phase stability, Na-vacancy, and charge ordering are key factors in material design.
• Controlling intermediate phases during desodiation is vital for optimizing electrode materials.