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

•Ultrathin Ni(OH)2 nanosheets (4–5 nm in thickness) were synthesized.•The Ni(OH)2 nanosheets show high capacitance, good rate and cycling performance.•The electrochemical performance is by far one of the best for Ni(OH)2.•The ultrathin morphology is beneficial to ion diffusion and charge transfer.

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.