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 NiCoOH/NiCoOOH composite film consisting of NiCoOH/NiCoOOH nanosheets on an expanded graphite paper (EGP) by using a facial anodization method. The as-prepared NiCoOH/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 NiCoOH/NiCoOOH nanosheets, and the synergistic effect of the NiCoOH and NiCoOOH phases and high conductive porous EGP. An aqueous asymmetric supercapacitor, assembled with the NiCoOH/NiCoOOH on EGP and Fe2O3 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.