Phosphorization coupled electrochemical activation substantially enhances the energy storage performance of high mass loading nickel–cobalt-based materials

It is crucial for next-generation energy storage devices to develop high performance electrode materials. For the real commercial application of supercapacitors, high mass loading, and high performance are expected at the same time. Herein, NiCo2O4 is directly grown on nickel foam (NiCo2O4/NF) via simple drying and annealing process. Then phosphorization and electrochemical activation (A-P-NiCo2O4/NF) were carried out, and the phase transformation and reaction mechanism were investigated. The etching of PO43- during activation generates unsaturated sites that trigger phase evolution behavior, resulting in self-optimization of the electrode and formation of polycrystalline, defect-rich nanostructures ((Ni,Co)OOH nanosheets), which greatly enhances the electrochemical activity. The electrochemical evaluation showed that the areal specific capacitance of A-P-NiCo2O4/NF with a high mass loading of 11.2 mg cm−2 was significantly enhanced (≈639%, from 1.7 to 10.86 F cm−2 at 1 mA cm−2). Meanwhile, the assembled quasi-solid-state A-P-NiCo2O4/NF//activated iron foam device exhibits a superior volumetric energy density of 10.68 mWh cm−3 at the power density of 14.17 mW cm−3. This work reveals the mechanism of phosphorus functionalization to enhance performance and provides a simple coupling approach to realize the enhancement in the energy storage of commercial-level bimetallic nickel–cobalt-based materials.