Fabrication of dual-functional electrodes using oxygen vacancy abundant NiCo2O4 nanosheets for advanced hybrid supercapacitors and Zn-ion batteries

Developing bimetal bifunctional electrodes with oxygen vacancies for next-generation high-performance supercapacitors and Zn-ion batteries with high security has attracted great attention. Herein, a binderless NiCo2O4 electrode with a 2D ultrathin nanosheet architecture and rich oxygen vacancies on an Ni foam substrate was designed (V-NiCo2O4-4), and demonstrated excellent electrochemical performance both in hybrid supercapacitors (HSCs) and Zn-ion batteries. Benefiting from the significantly improved conductivity and increased active site concentration, the optimized V-NiCo2O4-4 electrode delivers a remarkable specific capacity and favorable rate capability. When fabricated as a HSC, the installation delivers a high energy density of 57.1 W h kg−1, a maximum power density of 241.5 W kg−1, and outstanding cycling performance (91.9% capacity retention after 10 000 cycles). In addition, the V-NiCo2O4-4 electrode based Zn ion battery also offers a high energy density of 717.4 W h kg−1 and also delivers admirable durability (capacity retention of 98.8% after 2000 cycles). Density-functional theory (DFT) calculations reveal that the strong structural modulation strategy of oxygen vacancies effectively reduces the band gap in the Fermi level and widens the Co 3d orbital helping for improving electrochemical performance. This work provides a new foundation for the construction of high-performance binder-free battery-type electrodes for supercapacitors and aqueous rechargeable Zn batteries.