Proton‐Driven Effective Electric Potential Field Modulation for Ultrafast‐Charging Sodium‐Ion Batteries

ABSTRACT The fast charge–discharge capability of layered oxide cathodes is critical for their practical applications, but their intrinsic 2D structure results in high ionic transport barriers. Herein, we propose a protonation‐induced reconstruction strategy that boosts the effective electric potential by eliminating interfacial and bulk ion‐transport barriers in the NaNi 0.4 Fe 0.2 Mn 0.4 O 2 (NFM) cathode, delivering a comprehensive enhancement in fast‐charging performance. The introduction of Zr(HPO 4 ) 2 as a proton source enables the formation of a functional surface sheltering layer with 3D high‐speed ionic channels on NFM, which effectively removes surface residual alkali and thereby establishes a surface potential field that facilitates ultrafast ion transport. Concurrently, the transition metal–oxygen (TM─O) coordination in the bulk lattice is optimized, with the corresponding bond length shortened. This coordination optimization effectively lowers the internal ion‐transport resistance and shortens the diffusion pathways, enabling rapid bulk ion migration. As a result, the protonated‐reconstructed NFM cathode exhibits a high specific capacity of 94.4 mAh g −1 at an ultrahigh rate of 20C. This work provides fundamental insights into potential field engineering of layered oxide cathodes and presents a promising strategy for the design of high‐rate sodium‐ion battery materials.