Flexible and Mechanically Durable Asymmetric Supercapacitor Based on NiCo-Layered Double Hydroxide and Nitrogen-Doped Graphene Using a Simple Fabrication Method

A high-performing, lightweight, and flexible asymmetric supercapacitor (ASC) using NiCo-layered double hydroxide (NiCo LDH) supported on 3D nitrogen-doped graphene (NG) as a positive electrode and NG as a negative electrode is demonstrated. Highly conductive NG provides fast electron transfer and facilitates (dis)charging of NiCo LDH deposited on it. The composite electrode of NiCo LDH@NG exhibits a high specific capacitance of 1421 F g ⁻¹ at 2 A g ⁻¹ . Moreover, the as-obtained hybrid electrode shows an excellent rate capability with a specific capacitance of 1397 F g ⁻¹ at a high current density of 10 A g ⁻¹ , which is about 98% of the capacitance obtained at 2 A g ⁻¹ . The flexible ASC device shows a specific capacitance of 109 F g ⁻¹ at 0.5 A g ⁻¹ and a maximum energy density of 49 W h kg ⁻¹ , which is comparable with or superior to previously reported electrodes based on nickel-cobalt hydroxides. Furthermore, an excellent mechanical stability is obtained. Under repeated mechanical bendings, the ASC demonstrates high bending stability up to 450 bending cycles at a 90° angle. Hence, this flexible NiCo LDH@NG electrode that is free of binders and conductive agents shows superior performance and stability, and is a promising candidate for the future wearable energy storage devices.