Three-dimensional printing of the copper sulfate hybrid composites for supercapacitor electrodes with ultra-high areal and volumetric capacitances

How to prepare electrodes with high areal and volumetric capacitance is very significant for the daily use of supercapacitors. The booming additive manufacturing technology is well suited to this task. However, the selection of materials for 3D printing electrodes is still the focus of research. In this study, 2D layered graphene oxide (GO) was used as the binder and two kinds of 1D nanomaterials including MWCNTs and KCu7S4 were used as conductive and skeleton materials to prepare ink with excellent rheological properties through simple vacuum stirring. The electrodes were prepared by direct ink writing (DIW) printing, freeze drying, and simple chemical reduction. Herein, the 3D printed rGO/MWCNTs/KCu7S4 electrode has a special conductive cross-linking structure formed by self-combination. Among them, the 8-layer electrode at a current density of 0.5 A g−1 shows a gravimetric capacitance of 1674.3 F g−1, corresponding to the areal and volumetric capacitance of 27.8 F cm−2 and 73.1 F cm−3, respectively. This electrode has excellent capacitance retention, which could be achieved at 88.6% after 2000 successive cycles at 2 A g−1. Our work provides a simple and effective approach for the application of copper sulfate materials in DIW printing, and lays a good foundation for future application in supercapacitors and other electrochemical energy storage devices.Graphic abstract