Triple-shelled Ni@MnO/C hollow spheres with enhanced performance for rechargeable zinc-ion capacitors

Abstract

Electrochemical activation techniques and the use of multi-shell structured materials are effective strategies to enhance the electrochemical performance of rechargeable aqueous zinc-ion capacitors (ZICs). In this study, we successfully synthesized spherical Ni₃Mn-MOFs via a solvothermal method and used them as templates to prepare Ni/MnO@C nanospheres with different core–shell structures by adjusting the heating rate under an Ar atmosphere. The multi-shelled structure provides more active sites and alleviates structural strain associated with repeated Zn²⁺ insertion/extraction processes. During the initial charge process, the Ni/MnO@C cathode undergoes electrochemical activation and generates oxygen vacancies, which can facilitate Zn²⁺ adsorption and promote ion diffusion, significantly enhancing its initial capacity and cycling stability. The activated Ni/MnO@C electrode exhibits an excellent capacity of 500 mA h g⁻¹ at a current density of 0.3 A g⁻¹, and the capacity retention rate remains as high as 90.9% even after 5200 cycles at 3 A g⁻¹. The assembled AC//Ni/MnO@C (AC: active carbon) ZIC demonstrates an energy density of 90.14 W h kg⁻¹ at a power density of 2750.17 W kg⁻¹. At 3 A g⁻¹, the capacity retention rate remains as high as 80.3% after 6000 cycles, indicating excellent long-term durability. This work provides a promising strategy for designing high-performance cathodes for the next generation of ZICs.