Hierarchical 3D Zn-Ni-P nanosheet arrays as an advanced electrode for high-performance all-solid-state asymmetric supercapacitors

High-performance all-solid-state supercapacitors (SCs) have potential applications in modern electronics, such as portable and flexible electronics; however, their low specific capacity and operating voltage window limit their industrial applications. Herein, we developed a new type of zinc nickel phosphide nanosheet (Zn-Ni-P NS) arrays via a simple, scalable, and cost-effective hydrothermal and subsequent effective phosphorization technique to enhance the electrochemical performance of SCs. The hierarchical Zn-Ni-P NS array electrode exhibits an ultra-high specific capacity of ∼384 mA h g^-1 at a current density of 2 mA cm^-2 with excellent rate capability (79.43% of capacity retention at 50 mA cm^-2), and outstanding cycling stability (∼96.45% of capacity retention after 10000 cycles). Furthermore, the Zn-Ni-P NS//Fe₂O₃@NG all-solid-state asymmetric SC (ASC) delivers an ultra-high volumetric capacity of ∼1.99 mA h cm^-3, excellent energy density of ∼90.12 W h kg^-1 at a power density of 611 W kg^-1, and extraordinary cycling stability (93.05% of initial capacity after 20000 cycles at a high current density of 15 mA cm^-2). Such enhanced electrochemical performances are ascribed to the 3D hierarchical nanostructures, porous nanonetworks, improved conductivity, and synergistic interaction between the active components of Zn-Ni-P NS arrays.