Expedited Zn2+ diffusion in electrostatically shielded tunnels triples the capacity of spinel ZnMn2O4

Abstract

Strong electrostatic repulsion cripples Zn²⁺ diffusion in aqueous zinc-ion battery cathodes, particularly within rigid spinel frameworks where structural stability conflicts with ion kinetics. Here, we construct electrostatically shielded diffusion tunnels in spinel ZnMn₂O₄ (ZMO) via vacancy regulation. Electrostatic potential (ESP) mapping and density of states (DOS) analysis demonstrate that the obtained charge-depletion zones effectively reduce electrostatic repulsion along diffusion pathways during ion migration, lowering the Zn²⁺ diffusion barrier by 66% (from 0.76 eV to 0.26 eV) and enhancing the diffusion coefficient by two orders of magnitude (from 10⁻¹¹ cm² s⁻¹ to 10⁻⁹ cm² s⁻¹). The expedited Zn²⁺ diffusion in such electrostatically shielded tunnels triples the capacity of ZMO from 64 mAh g⁻¹ to 205 mAh g⁻¹ at 300 mA g⁻¹, with great cycling properties corresponding to a high-capacity retention of 93.7% over 200 cycles. More importantly, the assembled series-connected pouch cells also exhibit analogous capacity enhancement (from 9.1 mAh to 32.5 mAh) at 100 mA g⁻¹ with 93.4% retention after 100 cycles, outperforming other state-of-the-art zinc-ion pouch systems. This electrostatic regulation strategy establishes a new paradigm for designing high-capacity, fast diffusion kinetic cathodes for application in aqueous zinc batteries.