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.