Porous NiCoO2 nanospheres encapsulated in nitrogen-doped carbon shell achieving high energy storage for aqueous supercapacitors and zinc–ion batteries

The rational design of oxygen vacancies and electronic microstructures of electrode materials is crucial to promoting the energy storage performance. Herein, hierarchical urchin-like NiCoO 2 @N-C nanospheres assembled with mesoporous nanorods are reported as high-energy cathode materials to simultaneously satisfy the requirements of supercapacitors and zinc–ion batteries. Results show that the optimisation of annealing temperature in NiCoO 2 @N-C products can significantly adjust the composition, electronic structure and generate abundant oxygen vacancies. Benefiting from these merits, the as-synthesised NiCoO 2 @N-C electrode delivers excellent capacity (418 C g −1 at 1 A g −1 ) and long cycle performance (81% after 5000 cycles). Moreover, our fabricated NiCoO 2 @N-C//Zn battery presents an impressive specific capacity of 323 mAh g −1 and energy density of 226.1 Wh kg −1 . The energy storage and conversion mechanisms are also explored using the X-ray Absorption Fine Structure, in-situ Raman spectroscopy and ex-situ X-ray diffraction, probing subtle structural evolution of electrode materials during charge and discharge processes. This work may open a new avenue to design the nanomaterials with adjustable surface defects to accelerate various electrochemical reactions.