Asymmetric Cross-Orbital Coupling in Fe-Mn Spinels Decouples Structural Stability and Kinetics in Sodium-Ion Storage

The aqueous energy storage potential of transition metal oxides (TMOs) has long been hampered by the inherent trade-off between structural stability and reaction kinetics—a dilemma rooted in their antagonistic dependence on metal-oxygen (M-O) hybridization. Conventional strategies, constrained by the rigid linear correlation between M-O covalency and performance metrics, fail to decouple these competing properties. Here, we demonstrate an asymmetric cross-orbital coupling strategy to modulate electron distribution by precisely engineering Fe-O-Mn interactions in KxFeyMn1-yOz spinels. Combining density functional theory calculations with in situ spectroscopic characterization, we unveil the orbital coupling mechanism between Mn eg and Fe t2g states: selective redistribution of antibonding electron occupancy through orbital energy-level and spatial distribution differences, alongside an upshift of the O 2p band center that narrows the M-O orbital energy gap. This dual modulation effectively decouples structural and kinetic limitations. The optimized KFe0.15Mn0.85O2 electrode demonstrates a remarkable specific capacitance of 355.7 F g-1 at 1.0 A g-1, a 147% increase over the pristine material, with 86% retention after 30,000 cycles and a 40% lower Na+ migration barrier. This work provides a paradigm-shifting solution to the stability-kinetics dilemma in TMOs and opens new avenues for designing advanced energy materials that transcend classical hybridization constraints.