High-Performance, Flexible, All-Solid-State Wire-Shaped Asymmetric Micro-Supercapacitors Based on Three Dimensional CoNi₂S₄ Nanosheets Decorated–Nanoporous Ni–Zn–P Film/Cu Wire

Demand increasing for next generation portable and miniaturized electronics has aroused much interest to explore microscale and lightweight energy storage devices. Herein, we demonstrate successful development of flexible wire-shaped micro-supercapacitors (micro-SCs) based on novel CoNi₂S₄/E-NZP film@Cu wire electrode. The etched Ni–Zn–P (E-NZP) film was synthesized by directly deposition of NZP film on Cu wire, followed by a chemical etching process. Alkaline etching treatment provides a micro- and mesoporous structure with high surface area and facilitates the penetration of electrolyte ions into the electrode matrix. Then, CoNi₂S₄ nanosheets as electroactive material are electrochemically grown onto the E-NZP film@CW electrode under a constant potential. The synergistic effects contributed by various components inside the CoNi₂S₄/E-NZP@CW electrode deliver superior performances with a high specific capacitance of 1.12 F cm^–1, 8.9 F cm^–2, and 889.68 F cm^–3 at 4 mA cm^–2, outstanding rate capability (0.66 F cm^–1, 5.3 F cm^–2, and 529.02 F cm^–3 at 80 mA cm^–2) and long-term cycling stability (93.4% capacitance retention after 7000 cycles). Moreover, a flexible solid-state asymmetric micro-SC is fabricated using CoNi₂S₄/E-NZP film @CW as the positive electrode and rGO-coated carbon fiber (rGO/CF) as the negative electrode. The fabricated device exhibits high length, areal and volumetric capacitances of C_L: 40 mF cm^–1, C_A: 0.241 F cm^–2 and C_V: 18.54 F cm^–3, good mechanical stability with a maximum energy (E_L, 18 μW h cm^–1; E_A, 108.4 μW h cm^–2; and E_V, 8.34 mW h cm^–3), and power densities (P_L, 1454 μW cm^–1; P_A, 9280 μW cm^–2; and P_V, 716.9 mW cm^–3). This work provides a new and facile approach to develop high-performance wire-shaped electrodes as a new generation in energy storage applications.