Coupling N-doping and rich oxygen vacancies in mesoporous ZnMn₂O₄ nanocages toward advanced aqueous zinc ion batteries

The development of a high specific capacity and stable manganese (Mn)-based cathode material is very attractive for aqueous zinc-ion (Zn²⁺) batteries (ZIBs). However, the inherent low electrical conductivity and volume expansion challenges limit its stability improvement. Here, a mesoporous ZnMn₂O₄ (ZMO) nanocage (N-ZMO) coupled with nitrogen doping and oxygen vacancies is prepared by defect engineering and rational structural design as a high-performance cathode material for rechargeable ZIBs. The oxygen vacancies enhance the electrical conductivity of the material and the nitrogen doping releases the strong electrostatic force of the material to maintain a higher structural stability. Interestingly, N-ZMO exhibits excellent ability of Zn²⁺ storage (225.4 mAh·g⁻¹ at 0.3 A·g⁻¹), good rate, and stable cycling performance (88.4 mAh·g⁻¹ after 1,000 cycles at 3 A·g⁻¹). Furthermore, a flexible quasi-solid-state device with high energy density (261.6 Wh·kg⁻¹) is assembled, demonstrating long-lasting durability. We believe that the strategy in this study can provide a new approach for developing aqueous ZIBs.