Few-layered Ni(OH)₂ nanosheets for high-performance supercapacitors

Few-layered Ni(OH)₂ nanosheets (4-5 nm in thickness) are synthesized towards high-performance supercapacitors. The ultrathin Ni(OH)₂ nanosheets show high specific capacitance and good rate capability in both three-electrode and asymmetric devices. In the three-electrode device, the Ni(OH)₂ nanosheets deliver a high capacitance of 2064 F g^-1 at 2 A g^-1, and the capacitance still has a retention of 1837 F g^-1 at a high current density of 20 A g^-1. Such excellent performance is by far one of the best for Ni(OH)₂ electrodes. In the two-electrode asymmetric device, the specific capacitance is 248 F g^-1 at 1 A g^-1, and reaches 113 F g^-1 at 20 A g^-1. The capacitance of the asymmetric device maintains to be 166 F g^-1 during the 4000th cycle at 2 A g^-1, suggesting good cycling stability of the device. Besides, the asymmetric device exhibits gravimetric energy density of 22 Wh kg^-1 at a power density of 0.8 kW kg^-1. The present results demonstrate that the ultrathin Ni(OH)₂ nanosheets are highly attractive electrode materials for achieving fast charging/discharging and high-capacity supercapacitors.