Reduced Bond Covalency and Anisotropic Lattice Distortion Enable High Fe-Mn Redox Activation in a Mixed-Polyanionic...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Iron (Fe)- and Manganese (Mn)-based polyanionic compounds are cost-effective cathode materials for sodium-ion batteries (SIBs).
• The low redox potential of Fe2+/3+ and the Jahn-Teller (JT) effect in Mn2+/3+ hinder redox activation, limiting cycling stability and rate performance in SIBs.

Purpose of the Study:

• To investigate the synergistic effects of Fe-Mn redox activation and lattice distortion in a novel polyanionic material for SIBs.
• To enhance the energy density, rate capability, and cycling stability of sodium storage materials.

Main Methods:

• Synthesis and characterization of Na4Mn1.5Fe1.5(PO4)2(P2O7) (NMFPP) material.
• Experimental and theoretical studies (e.g., DFT) to analyze redox behavior, electronic structure, and ion diffusion.
• Electrochemical testing to evaluate battery performance.

Main Results:

• Achieved high Mn2+/3+ and Fe2+/3+ redox activation in NMFPP.
• Mn substitution reduced Fe-O bond covalency, increasing Fe2+/3+ redox potential and energy density.
• Anisotropic lattice distortion enlarged Na+ diffusion pathways, lowering barriers for rapid Na+ migration.
• NMFPP demonstrated enhanced energy density, rate performance, and exceptional cycling stability.

Conclusions:

• The Jahn-Teller effect and lattice distortion can synergistically enhance transition-metal redox activation in electrode materials.
• This work provides insights for designing high-performance cathode materials for sodium-ion batteries.