In Situ Growth of 2D Ultrathin NiCo2 O4 Nanosheet Arrays on Ni Foam for High Performance and Flexible Solid-State Supercapacitors.

In order to further overcome the shortage of electrodes with additive/binder and modulate the structure of NiCo2 O4 for supercapacitors, ultrathin NiCo2 O4 nanosheet arrays have been in situ grown on Ni foam by optimizing hydrothermal reactions based on crystal growth dynamics. The structure of ultrathin NiCo2 O4 nanosheet arrays can expose more active sites, provide abundant diffusion channels and buffer the stress caused by phase transition during charge-discharge process of supercapacitors. The optimized hydrothermal reactions can provide more ordered crystal orientations by keeping nanosheets on Ni foam completely coming from in situ growth, which will decrease the inner resistance of ultrathin NiCo2 O4 nanosheets and improve the efficiency and kinetics of electrons transfer. By the virtue of such remarkable features, the electrochemical results confirm the rationality of structural modulation and crystal orientations optimization with a drastically enhanced specific capacitance of 2017.8 F g-1 , admirable rate performance of 93.2% and outstanding stability retention of 90.9% after cycling 5000 times. More impressively, the assembled flexible solid-state asymmetric supercapacitor (ASC) shows superior energy density, power density, and high stability. The modification strategy in this paper may throw light on the rational design of new generation advanced electrode materials for high-performance flexible supercapacitors.