Rate capability improvement of Co−Ni double hydroxides integrated in cathodically partially exfoliated graphite

In-situ growing of energy storage materials on graphene-based substrates/current collectors with low defect is a good way to boost electron transport and so enhance rate capability for the obtained electrode. Herein, high-quality graphene-like nanopetals are partially exfoliated from graphite foil (GF) through a facile and fast cathodic process. Three-dimensional porous structure is established for the afforded cathodically-exfoliated graphite foil (CEG), with many graphene-like nanopetals vertically anchoring on the graphite substrate. A hierarchical structure is constructed by the following electrochemical growth of Co−Ni double hydroxide nanopetals on the graphene atop CEG. The double hydroxide in the obtained electrode with the optimized Co 2+ /Ni 2+ molar ratio , Co 0.75 Ni 0.25 (OH) 2 -CEG, displays much improved rate capability and so can deliver a high specific capacitance of 1460 F g −1  at an ultra-high current density of 100 A g −1 . An asymmetric device is assembled by using Co 0.75 Ni 0.25 (OH) 2 -CEG as cathode, which demonstrates a high energy density of 31.6 Wh kg −1  at an ultra-high power density of 21.5 kW kg −1 , showing the potential of the hierarchical composite electrode for high power application. The device also displays good stability, it can retain more than 90% of its capacitance after 10000 galvanostatic charge-discharge cycles.