Constructing Crystalline NiCoP@Amorphous Nickel-Cobalt Boride Core-Shell Nanospheres with Enhanced Rate Capability for Aqueous Supercapacitors and Rechargeable Zn-Based Batteries

Rational design and fabrication of efficient electrode materials can significantly enhance the electrochemical performance of supercapacitors and alkaline Zn-based batteries, especially under high current density. Herein, the crystalline/amorphous nickel-cobalt phosphide@nickel-cobalt boride core-shell nanospheres (NiCoP@NiCo-B) are successfully synthesized by integrating the nanosheet-assembled NiCoP hollow nanospheres (core) with amorphous NiCo-B (shell). Meanwhile, the crystalline NiCoP core can provide stable mechanical support, and the amorphous NiCo-B shell favors the electrolyte ion diffusion. The well-designed NiCoP@NiCo-B heterostructure demonstrates strong interface interactions, abundant redox active sites, and fast charge transfer/transport kinetics. The optimal electrode (NiCoP@NiCo-B-70) delivers a specific capacity as high as 193.1 mAh g^-1 at 1 A g^-1 and ultrahigh rate capability (87.4% of the initial specific capacity at 20 A g^-1). The assembled NiCoP@NiCo-B-70//AC asymmetric supercapacitor reaches an energy density of 40.8 Wh kg^-1 and power density of 400.0 W kg^-1. Furthermore, the NiCoP@NiCo-B-70//Zn battery shows a high output voltage platform and a discharge capacity of 194.5 mAh g^-1 at a current density of 1 A g^-1 as well as outstanding rate capability. The results indicate that the synthesized crystalline/amorphous core-shell heterostructure holds great potential for practical applications in next-generation aqueous energy storage devices.