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 K_xFe_yMn_1−yO_z spinels. Combining density functional theory calculations with in situ spectroscopic characterization, we unveil the orbital coupling mechanism between Mn e_g and Fe t_2g 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 KFe_0.15Mn_0.85O₂ 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.