Decoupling TM-O Antibonding via Targeted Orbital Engineering Enables High-Voltage and Long-Life Sodium Polyanionic...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Polyanionic cathode materials with Mn/V redox couples offer high energy density for sodium-ion batteries (SIBs).
• These materials exhibit poor rate capability and cycling stability at high voltages due to unclear electronic-level degradation mechanisms.

Purpose of the Study:

• To elucidate the electronic-level origin of degradation in high-voltage polyanionic SIB cathodes.
• To develop a strategy for enhancing the stability and performance of these cathode materials.

Main Methods:

• Investigated the electronic structure and orbital interactions within Mn/V-based polyanionic materials.
• Employed targeted orbital engineering by introducing Ti4+ and Fe3+ ions and Si substitution.
• Synthesized and characterized the optimized cathode material: Na4Mn0.7V0.7Ti0.4Fe0.2(PO4)2.9(SiO4)0.1.

Main Results:

• Revealed strong coupling between Mn/V-O antibonding orbitals induces lattice strain and kinetic hysteresis at elevated voltages.
• Orbital engineering successfully modulated (TM-O)* orbital occupancy, alleviating structural stress.
• The optimized cathode demonstrated a high energy density of 415.03 Wh/kg.
• Achieved exceptional long-cycle performance, retaining 80.3% capacity after 8,000 cycles at 20 C.

Conclusions:

• Orbital engineering is a viable strategy to overcome the limitations of high-voltage polyanionic cathodes for SIBs.
• The developed cathode material exhibits promising potential for high-energy-density and stable sodium-ion energy storage.
• This work provides a new avenue for designing advanced cathode materials through electronic structure manipulation.