Hierarchical Bimetallic Hydroxides Built by Porous Nanowire‐Lapped Bundles with Ultrahigh Areal Capacity for Stable Hybrid Solid‐State Supercapacitors

Abstract Exploring advanced electrode materials with superb energy/power densities and long lifetime as well as low cost is the recent focus of hybrid solid‐state supercapacitor (HSSC). This study reports a novel hierarchical bimetallic hydroxide (Ni₁Co₁‐OH) built by nanowire‐lapped bonfire‐like bundles through a facile and scalable method, and provides thorough insights into possible formation mechanism and structural merits of the interesting hierarchical architecture. Benefiting from multistep redox reactions, high accessible surface area and fast kinetics contributed by the unique structure, Ni₁Co₁‐OH using 2 m KOH electrolyte can achieve highly improved gravimetric capacity/capacitance of 876.8 C g⁻¹/1753.6 F g⁻¹ at active mass loading of 3 mg cm⁻² at 1 A g⁻¹, and especially deliver a record‐high areal capacity of 7.6 C cm⁻² at 1 A g⁻¹ under a commercial loading of 15 mg cm⁻². 1.5 V Ni₁Co₁‐OH based HSSC with the poly(vinyl alcohol)/KOH gel electrolyte verifies the intriguing performance including high energy/power densities of 27.9 Wh kg⁻¹/13812.9 W kg⁻¹, a long life over 10 000 cycles, and a low self‐discharge rate with a voltage decline of 20% after 24 h. The findings identify the scalable production of high‐performance bimetal compounds, which will boost the development of highly demanding HSSC devices.