Interfacial Control of NiCoP@NiCoP Core–Shell Nanoflake Arrays as Advanced Cathodes for Ultrahigh‐Energy‐Density Fiber‐Shaped Asymmetric Supercapacitors

Abstract Efficient improvement of the energy density and overall electrochemical performance of fiber‐shaped asymmetric supercapacitors (FASCs) for practical applications in portable and wearable electronics requires highly electrochemically active materials and a rational design. Herein, two‐step phosphorization (TSP) processes are performed to directly grow 3D well‐aligned NiCoP@NiCoP (NCP@NCP TSP) nanoflake arrays (NFAs) on carbon nanotube fibers (CNTFs). Profiting from the metallic characteristics and excellent electrochemical performance of NiCoP and the hierarchical design of the core–shell heterostructure, the NCP@NCP TSP NFAs/CNTF hybrid electrode exhibits significantly improved electrochemical performance. The as‐fabricated NCP@NCP TSP NFAs/CNTF electrode possesses an ultrahigh areal capacitance of 10 035 mF cm −2 at a current density of 1 mA cm −2 , with excellent rate capability and cycling stability. Furthermore, an FASC device with a maximum operating voltage of 1.6 V is assembled by adopting NCP@NCP TSP NFAs/CNTF as a positive electrode, hierarchical TiN@VN core–shell heterostructure nanowire arrays (NWAs)/CNTF as negative electrode, and KOH‐PVA as a gel electrolyte. The FASC device exhibits a high areal capacitance of 430.4 mF cm −2 and an ultrahigh energy density of 51.02 mWh cm −3 . Thus, the rationally designed NiCoP@NiCoP electrode is a promising candidate for incorporation into next‐generation wearable and portable energy‐storage devices.