Ultrathin NiCo-layered double hydroxide nanosheets arrays vertically grown on Ni foam as binder-free high-performance supercapacitors

A binder-free and high-performance supercapacitor was designed, in which 3D ultrathin nickel cobalt layered double hydroxide (NiCo-LDH) nanosheets were vertically grown on Ni foam using a facial one-step hydrothermal route. The phase of NiCo-LDH can be tuned from single alpha phase to multiphase (alpha and beta) by only changing the volume ratio of solvent. Compared to the NiCo-LDH with single alpha phase (1812 F/g), the multiphase NiCo-LDH shows an ultrahigh specific capacitance of 2617 F/g at 1 A/g. The multiphase one remained 1562 F/g at 10 A/g, showing a good rate capability of about 60%. Importantly, the poly-phase NiCo-LDH/NF supercapacitor electrodes displayed favorable capacitive behaviors of 70% after 1300 cycles at 10 A/g. Moreover, the multiphase NiCo-LDH/NF and activated carbons were assembled into asymmetric supercapacitor device which with a high specific capacitance of 439.5 mF/cm(2) at a current density of 2 mA/cm(2). The enhancement of electrochemical performance is mainly ascribed to distinguishingly multilayered structure and mixed crystal phase.