Rational construction of NiCo double-hydroxide/cobalt hydroxycarbonate as advanced electrode for high performance asymmetric supercapacitor

In this present paper, a novel nickel‑cobalt double hydroxide/cobalt carbonate hydroxide nanosheets composite (NiCo-DH/NSs) with excellent electrochemical performances is successfully constructed through a rational design of the structure and composition. Cobalt carbonate hydroxide (Co2(OH)2CO3) with a nanosheet morphology and low surface energy is firstly prepared by an simple one-step hydrothermal approach. Then the electroconductive NSs are exploited as a substrate for the in-situ growth of metal-organic framework (MOF). The pre-synthesized MOF/NSs composite is further alkali treated to obtain the final composite material by a “crystal-crystal conversion” strategy. Due to proper structure and synergistic effect between two components, the prepared NiCo-DH/NSs as positive electrode material delivers a high specific capacity (586 mAh g−1 at 1 A g−1) and outstanding rate performance (92.15 % capacity retention at 10 A g−1). In addition, a high specific capacitance of negative electrode material (BiOBr microsphere) is also successfully prepared. As a result, the assembled NiCo-DH/NSs//BiOBr asymmetric supercapacitor (ASC) device exhibits ultrahigh energy density of 67.74 Wh kg−1 at power density of 775.03 W kg−1.