Facile anodization approach derived low-crystalline NiCoOH/NiCoOOH composite films for ultra-high areal capacity and mass loading supercapacitors

The design of supercapacitor materials with both high areal capacity ( C ) and high mass loading is vitally important for enhancing energy density ( E ). Herein, we prepared a NiCo OH/NiCoOOH composite film consisting of NiCo OH/NiCoOOH nanosheets on an expanded graphite paper (EGP) by using a facial anodization method. The as-prepared NiCo OH/NiCoOOH film exhibits ultra-high C of 11 mA·h·cm −2 at a mass loading of 165 mg·cm −2 , high rate capability of 71% and excellent cycling stability of 95% after 12 000 cycles. The outstanding performance is ascribed to the low-crystalline feature of the NiCo OH/NiCoOOH nanosheets, and the synergistic effect of the NiCo OH and NiCoOOH phases and high conductive porous EGP. An aqueous asymmetric supercapacitor, assembled with the NiCo OH/NiCoOOH on EGP and Fe 2 O 3 on EGP as positive- and negative-electrode, respectively, shows a highest E of 3.8 mW·h·cm −2 at a power density ( P ) of 4 mW·cm −2 and a maximum P of 107 mW·cm −2 at an E of 2.7 mW·h·cm −2 .