Enhanced Structural Stability of Nickel–Cobalt Hydroxide via Intrinsic Pillar Effect of Metaborate for High-Power and Long-Life Supercapacitor Electrodes

Layered α-Ni­(OH)₂ and its derivative bimetallic hydroxides (e.g., α-(Ni/Co)­(OH)₂) have attracted much attention due to their high specific capacitance, although their insufficient cycling stability has blocked their wide application in various technologies. In this work, we demonstrate that the cycling performance of α-(Ni/Co)­(OH)₂ can be obviously enhanced via the intrinsic pillar effect of metaborate. Combining the high porosity feature of the metaborate stabilized α-(Ni/Co)­(OH)₂ and the improved electronic conductivity offered by graphene substrate, the average capacitance fading rate of the metaborate stabilized α-(Ni/Co)­(OH)₂ is only ∼0.0017% per cycle within 10 000 cycles at the current density of 5 A g^–1. The rate performance is excellent over a wide temperature range from −20 to 40 °C. We believe that the enhancements should mainly be ascribed to the excellent structural stability offered by the metaborate pillars, and the detailed mechanism is discussed.