Rational design of honeycomb Ni-Co LDH/graphene composite for remarkable supercapacitor via ultrafast microwave synthesis

Nickel cobalt layered double hydroxide (Ni-Co LDH) is an exciting new electrode material because of its high theoretical capacity and redox activity. However, the complicated synthesis process and the intrinsically low conductivity impede its large-scale commercial application. Hence, a high-efficiency microwave liquid synthesis method was employed to rapidly prepare honeycomb-structured Ni-Co LDH nanosheets on graphene (Ni-Co LDH/G) composite, within minutes range of synthesis time. By introducing graphene, the poor intrinsic conductivity of the Ni-Co LDH could be ameliorated by hybridization effect, as reveled by density functional theory calculations, thus enhancing the rate capability greatly: Ni-Co LDH/G composite retained 87.1% of capacity at high rate, whereas only 50.5% was retained for Ni-Co LDH. In addition, the hybrid supercapacitor with Ni-Co LDH/G//activated carbon could deliver a high energy density of 40.6 Wh kg−1 at 400 W kg−1, along with a stable cycling lifespan with 83.2% of capacity retention after 10,200 cycles. These encouraging findings highlight that microwave synthesis could be an efficient route to engineer coordinating Ni-Co LDH/G composite for advanced electrode materials in supercapacitors.