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.