Rational Design of Three‐Dimensional Hierarchical Nanomaterials for Asymmetric Supercapacitors

The low energy density of supercapacitors has become a distinct barrier, restricting their practical applications. To overcome it, rational design of three-dimensional (3D) hierarchical materials for asymmetric supercapacitors is considered to be an effective strategy from the view of both materials and device design. Through rational design, desirable supercapacitive electrode materials with enlarged specific surface areas, shortened ion-diffusion distances, and improved electrical conductivity can be achieved, which exhibit potential prospects in constructing high-performance supercapacitors. This Review presents the state-of-the-art progress upon rational design of 3D hierarchical structures in the last five years. The typical 3D hierarchical nanomaterials in the forms of homogeneous and heterogeneous nanostructures are highlighted and classified into primary structures, secondary structures, and multiple structures. Besides, the realization and growth mechanism have been discussed. At the end of this Review, some possible future tendencies are proposed as well.