Template-Free Preparation of α-Ni(OH)2 Nanosphere as High-Performance Electrode Material for Advanced Supercapacitor

Mesoporous Cubic Nanocages Assembled by Coupled Monolayers With 100% Theoretical Capacity and Robust Cycling

High capacity and long cycling often conflict with each other in electrode materials. Despite extensive efforts in structural design, it remains challenging to simultaneously achieve dual high electrochemical properties. In this study, we prepared brand-new completely uniform mesoporous cubic-cages assembled by large d-spacing Ni(OH)2 coupled monolayers intercalated with VO4 3- (NiCMCs) using a biomimetic approach. Such unique mesoporous structural configuration results in an almost full atomic exposure with an amazing specific surface area of 505 m2/g and atomic utilization efficiency close to the theoretical limit, which is the highest value and far surpasses all of the reported Ni(OH)2. Thus, a breakthrough in simultaneously attaining high capacity approaching the 100% theoretical value and robust cycling of 10,000 cycles is achieved, setting a new precedent in achieving double-high attributes. When combined with high-performance Bi2O3 hexagonal nanotubes, the resulting aqueous battery exhibits an ultrahigh energy density of 115 Wh/kg and an outstanding power density of 9.5 kW/kg among the same kind. Characterizations and simulations reveal the important role of large interlayer spacing intercalation units and mesoporous cages for excellent electrochemical thermodynamics and kinetics. This work represents a milestone in developing "double-high" electrode materials, pointing in the direction for related research and paving the way for their practical application.

Hierarchical core-shell nickel hydroxide@nitrogen-doped hollow carbon spheres composite for high-performance hybrid supercapacitor

Designing electrode materials with high performance and maximum utilization is of great desire for supercapacitors, which highly depend on the intrinsic electrochemical properties and the optimal frameworks of the electrode materials. The hierarchical core-shell structure with various types of pores can make the most of the electrode material due to the easy access of electrolyte into the interior electrode and large exposure of electrode into the electrolyte. In this work, nickel hydroxide@nitrogen-doped hollow carbon spheres (Ni(OH)₂@NHCSs) electrode material with a hierarchical core-shell structure was obtained using a hard template and the following chemical-precipitation method. Ni(OH)₂@NHCSs electrode displays an excellent specific capacity of 214.8 mA h g^-1 (that is 1546.6 F g^-1), higher than the Ni(OH)₂ counterpart (108.9 mA h g^-1, that is 784.1 F g^-1) at 1 A g^-1 in 2 M KOH electrolyte. The assembled Ni(OH)₂@NHCSs||NHCSs hybrid supercapacitor (HSC) delivers an energy density of 37.5 W h kg^-1 at 800.0 W kg^-1 and an outstanding stability with 79.2% of retention rate for 10,000 cycles at a current density of 8 A g^-1. The Ni(OH)₂@NHCSs electrode exhibits excellent electrochemical performance primarily contributed by its unique hierarchical core-shell structure, high specific surface area and enhanced electrical conductivity.