From Static Symmetry to Intrinsic Polarization: Engineering Dipole Fields in MnO2 for Enhanced Zn2+ Intercalation Kinetics and Structural Reversibility.

The centrosymmetric structure of layered δ-MnO2 cathodes severely restricts Zn2+ transport kinetics in aqueous zinc-ion batteries (AZIBs). Herein, we demonstrate a transition from static local symmetry to intrinsic polarization by engineering a built-in dipole polarization field through Mo doping. This symmetry-breaking strategy generates oriented Mo-O-Mn dipoles that self-assemble into a continuous internal electric field, driving directional electron delocalization and enriching lattice oxygen with excess electron density. Consequently, the O p-band center downshifts from -1.82 to -2.40 eV, reconfiguring the [MnO6] octahedral electronic structure and substantially reducing the Zn2+ diffusion barrier. The Mo-modified MnO2 (MMO) electrode delivers a reversible capacity of 348 mAh g-1 at 0.2 A g-1 with 95% retention over 200 cycles, and crucially, exhibits superior structural reversibility with reversible recovery of oxygen-related species during cycling. This work establishes the O p-band center as a key electronic descriptor and demonstrates intrinsic dipole-field engineering as an effective strategy for improving Zn2+ intercalation kinetics and structural reversibility in MnO2 cathodes.