High mass loading NiCo2O4 with shell-nanosheet/core-nanocage hierarchical structure for high-rate solid-state hybrid supercapacitors

Rational design of advanced structure for transition metal oxides (TMOs) is attractive for achieving high-performance supercapacitors. However, it is hampered by sluggish reaction kinetics, low mass loading, and volume change upon cycling. Herein, hierarchical NiCo2O4 architectures with 2D-nanosheets-shell and 3D-nanocages-core (2D/3D h-NCO) are directly assembled on nickel foam via a facile one-step way. The 2D nanosheets are in-situ generated from the self-evolution of initial NCO nanospheres. This 2D/3D hierarchical structures ensure fast ion/ electron transport and maintain the structural integrity to buffer the volume expansion. The 2D/3D h-NCO electrode with an ultrahigh mass loading (30 mg cm(-2)) achieves a high areal capacity of 4.65 C cm(-2) (equivalent to 1.29 mAh cm(-2)) at a current density of 4 mA cm(-2), and retains 3.7 C cm(-2) even at 50 mA cm(-2). Furthermore, the assembled solid-state hybrid supercapacitor yields a high volumetric energy density of 4.25 mWh cm(-3) at a power density of 39.3 mW cm(-3) , with a high capacity retention of 92.4% after 5000 cycles. Therefore, this work provides a new insight to constuct hierarchical electrodes for energy storage application. (C) 2020 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.