Tunable Zn ²⁺ /Mn ³⁺ Vacancy Engineering in ZnMn ₂ O ₄ Cathodes Boosts Zn ²⁺ Kinetics for High-Performance Aqueous Zinc-Ion Batteries

Spinel-type ZnMn2O4 cathodes for aqueous zinc-ion batteries (AZIBs) offer high theoretical capacity and elemental abundance, yet their electrochemical performance is fundamentally hindered by Mn dissolution-induced structural instability and sluggish Zn2+ diffusion kinetics. Herein, we propose a tunable cationic vacancy engineering strategy for ZnMn2O4 cathodes, enabling selective introduction of Zn2+ or Mn3+ vacancies via a facile chemical coprecipitation method. Comprehensive characterizations confirm that these cationic vacancies significantly enhance electronic conductivity and accelerate Zn2+ diffusion kinetics. Specifically, the Zn-vacant Zn1–xMn2O4 cathode outperforms its Mn-vacant counterpart, leveraging strengthened Mn–O bonding and reduced electrostatic repulsion during Zn2+ insertion, delivers a high reversible capacity of 276.4 mAh g–1 at 0.5 A g–1, exceptional rate capability (retain 134.4 mAh g–1 at 2 A g–1), and long-term cyclability with 92% capacity retention after 2000 cycles at 2 A g–1. Furthermore, a prototype pouch cell incorporating this engineered cathode achieves a superior capacity of 150 mAh g–1 at 0.5 A g–1, demonstrating its great potential for practical high-performance AZIBs.