Facile anodization approach derived low-crystalline NiCo-OH/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 center dot h center dot cm(-2) at a mass loading of 165 mg center dot 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 Fe2O3 on EGP as positive-and negative-electrode, respectively, shows a highest E of 3.8 mW center dot h center dot cm(-2) at a power density (P) of 4 mW center dot cm(-2) and a maximum P of 107 mW center dot cm(-2) at an E of 2.7 mW center dot h center dot cm(-2). (c) 2022 The Authors. Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).