Development of High-Performance Iron-Based Phosphate Cathodes toward Practical Na-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Iron-based phosphates are promising low-cost cathode materials for sodium-ion batteries (SIBs).
• Existing Na4Fe3(PO4)2(P2O7) materials suffer from limited electrochemical performance and energy density.
• The practical application of these materials is hindered by insufficient performance.

Purpose of the Study:

• To develop a new iron-based phosphate cathode material with enhanced electrochemical properties.
• To investigate the potential of intergrown heterostructures for improving SIB performance.
• To address the limitations of current iron-based phosphate cathodes for SIBs.

Main Methods:

• Synthesis of Na4.5Fe3.5(PO4)2.5(P2O7) with an intergrown heterostructure of maricite-type NaFePO4 and orthorhombic Na4Fe3(PO4)2(P2O7) phases.
• Electrochemical characterization including reversible capacity and energy density measurements.
• Long-term cycling stability tests in pouch cells.

Main Results:

• The new Na4.5Fe3.5(PO4)2.5(P2O7) composite cathode exhibits a reversible capacity exceeding 130 mA h g-1 and an energy density near 400 W h kg-1.
• These values significantly surpass those of the single-phase Na4Fe3(PO4)2(P2O7) cathode (approx. 120 mA h g-1 and 350 W h kg-1).
• The material demonstrates stable cycling performance over 2000 cycles at 3 C in pouch cells, with kg-level production achieved.

Conclusions:

• The developed Na4.5Fe3.5(PO4)2.5(P2O7) material shows superior electrochemical performance compared to existing iron-based phosphates.
• The intergrown heterostructure design is effective in boosting capacity and energy density for sodium-ion batteries.
• This research provides a promising pathway for the practical implementation of advanced iron-based phosphate cathodes in sodium-ion batteries.