Stability-Enhanced α-Ni(OH)₂ Pillared by Metaborate Anions for Pseudocapacitors

α-Ni(OH)2 is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO2–-intercalated α-NixCo(1–x)(OH)2 is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO2– enhances the bonding with metal ions and attracts water molecules. Thus, the BO2– ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni(OH)2. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni(OH)2 exhibits the specific capacitance of 2179, 1592, and 1423 F·g–1 at 1, 20, and 40 A·g–1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg–1 when its power density is 187.06 W·kg–1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g–1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni(OH)2 confronts broader fields of application.