Evaluating the Role of Nanostructured Current Collectors in Energy Storage Capability of Supercapacitor Electrodes with Thick Electroactive Materials Layers

Electroactive materials (especially pseudocapacitive materials) are generally in the form of ultrathin conformal coating in supercapacitor electrodes based on nanostructured current collectors; thus, the resultant low mass loading of electroactive materials largely limits the applications of nanostructured current collectors. Here, supercapacitor electrodes with nickel nanorod arrays as nanostructured current collectors and MnO2 as electroactive materials are fabricated to study the role of nanostructured current collectors in determining the energy storage capability when electroactive materials are in thick layer rather than ultrathin conformal coating. Electrochemical analysis reveals that Ni nanorods could create numerous electrical conductive tunnels in the thick-layer electrodes to dramatically alleviate the contact resistance at the electroactive-material/current-collector interface. With 1 mu m thick MnO2 layer, the Ni nanorods based electrodes have much higher areal capacitance than those with Ni foils as current collectors, which is more than six times of that with the same MnO2 mass loading or more than 18 times of that with the same 1 mu m thick MnO2 layer. Moreover, better rate capability and higher structural stability is maintained in Ni nanorods based electrodes even with 3 mu m thick MnO2 layer. These results open up new opportunities for nanostructured current collectors to construct supercapacitors with superior energy storage capability.