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

Polyanionic cathode materials based on Mn/V redox couples offer high-voltage plateaux and high theoretical energy density for sodium-ion batteries (SIBs). However, they suffer from severe degradation in rate capability and cycling stability under high-voltage, whose microscopic origin remains elusive on the electronic-level. Herein, we reveal the strong coupling between Mn/V-O antibonding orbitals at elevated voltages induces significant lattice strain, leading to kinetic hysteresis. Thus, we propose a targeted orbital engineering regulation strategy aiming to disentangle the strong coupling among (TM-O)* orbitals. By introducing Ti4+ (3d0) and Fe3+ (3d5) as the stable electronic configurations, and electron-donating Si, we modulate (TM-O)* orbital occupancy at the electronic level, markedly alleviating structural stress and stabilizing Na+ diffusion pathways. The optimized Na4Mn0.7V0.7Ti0.4Fe0.2(PO4)2.9(SiO4)0.1 cathode delivers high energy density (415.03 Wh/kg) and exceptional long-cycle performance, retaining 80.3% capacity after 8,000 cycles at 20 C. This strategy demonstrates a feasible orbital engineering approach to develop stable high-energy-density cathodes for SIBs.