Hierarchical hollow nanocages of Ni–Co amorphous double hydroxides for high-performance asymmetric supercapacitors

Recently, increasing attention has been drawn to the amorphous nanomaterials due to their abundant exposed active sites and ion transport channels compared to the crystalline counterparts. Herein, we firstly use amorphous Ni–Co amorphous double hydroxides (Ni–Co ADHs) hollow cages as a positive electrode material to build up supercapacitors (SCs). Owing to the unique structure, amorphous nature and synergetic effects, the obtained product achieves a high capacitance up to 1198 F g⁻¹ at 1 A g⁻¹ and excellent rate capacity (64.3% capacitance retention at 20 A g⁻¹). Moreover, the asymmetric supercapacitor (ASC) consisted of Ni–Co ADHs and reduced graphene oxide (rGO) hydrogel as positive and negative electrode, respectively, exhibits a maximum energy density of 35 Wh kg⁻¹, a maximum power density of 8770 W kg⁻¹, as well as the capacitance retention of 84.3% over 5000 cycles, which exceeds the most other Ni or Co-based SCs. Our work sheds light on structural design and practical application of amorphous nanomaterials in energy storage devices.