Nanoscale nickel phosphide encapsulated in carbon microsphere from a spherical MOF toward high-performance supercapacitors

Transition metal phosphides (TMPs) are considered excellent candidate electrode materials for supercapacitors (SCs) due to their high theoretical capacity. However, the severe performance degradation of TMPs, originating from poor conductivity and resulting volumetric expansion under electrochemical conditions, hinders the practical and large-scale application in supercapacitor electrodes. Herein, a robust heterostructure of nanoscale nickel phosphide encapsulated in carbon microsphere (Ni2[email protected]) is constructed through the carbonization of spherical Ni-MOF, and followed by subsequent low-temperature phosphorylation. The MOF-derived uniform carbon layer on the Ni2P surface provides massive electron transport channels and physically restricts the volumetric expansion during electrochemical reactions, facilitating the electrode reaction kinetics and further leading to a good capacitive performance in high capacitance (1622 F/g at 1 A/g), long-term cyclic stability (75.2% capacitance retention after 8000 cycles at 20 A/g), and high rate capability. Furthermore, asymmetric SCs based on Ni2[email protected] and AC exhibit a high capacitance of 135.4 F/g at 0.5 A/g, and a remarkable energy density of 47.46 Wh/kg at a power density of 0.397 kW/kg with the excellent cyclic property. These results demonstrate that the methodology is highly promising in the design and construction of Ni2P/carbon hybrid electrodes, revealing an attractive candidate electrode material in high-property energy-storage devices.