NiCo 2 O 4 /C Core‐Shell Nanoneedles on Ni Foam for All‐Solid‐State Asymmetric Supercapacitors

Abstract Herein, NiCo 2 O 4 /C core‐shell nanoneedles grown on Ni foam are prepared by a simple route and applied in supercapacitors. Electrochemical results show that the area specific capacitance of NiCo 2 O 4 /C reaches 2057 mF/cm 2 at 1 mA/cm 2 , which is about 4 times than that of the pristine NiCo 2 O 4 . The electrode exhibits excellent rate capability (92 % of capacitance retention at 10 mA/cm 2 ) and remarkable cycling stability (81 % of capacitance retention after 10000 cycles). The as‐fabricated all‐solid‐state asymmetric supercapacitor (NiCo 2 O 4 /C//AC(active carbon)) achieves an energy density of 2 mW h cm −3 at a power density of 37 mW cm −3 and remains 1.6 mW h cm −3 at a power density of 120 mW cm −3 . Moreover, the ASC device can retain 87 % capacitance after 4000 cycles. The result reveals that it is a feasible method to achieve excellent performance in energy storage devices by the dipping method.