Dual‐Functional Ca‐Ion‐Doped Layered δ‐MnO 2 Cathode for High‐Performance Aqueous Zinc‐Ion Batteries

Aqueous zinc‐ion batteries (ZIBs) have gained significant attention owing to their high energy densities, low costs, and enhanced safety profiles. However, the development of suitable host materials (i.e., cathodes) with high capacity, structural stability, and rate performance remains challenging. Herein, a nanoflower‐like Ca 0.10 MnO 2 ·0.61H 2 O (CaMnO) is successfully synthesized as a high‐performance cathode material for ZIBs using a simplified one‐step hydrothermal method. The unique nanoflower‐like 3D porous structure provides a continuous conductive path and abundant adsorption sites for Zn 2+ ions and mitigates aggregation during long‐term cycling processes. In addition, doping Ca 2+ ions into the interlayer of MnO 2 has a dual functional effect: 1) it acts as a pillar to broaden the interlayer spacing and enhance the crystal structure stability, and 2) it induces the formation of oxygen vacancies to enhance the reaction kinetics and increase the reversible capacity. Therefore, the CaMnO cathode exhibits a high specific capacity of 289 mAh g −1 , with excellent capacity retention (90%) over 750 cycles at a high current rate of 1.5 A g −1 . This study provides a new perspective on the development of advanced cathode materials for ZIBs.