Design and Fabrication of Carbon-Based Printable Inks for All-Solid-State Supercapacitors with High Capacitance and High Flexibility

Aqueous flexible supercapacitors (AFSCs) are considered to be a promising power source for wearable electronics due to their fast charging, superior stability, and high safety. However, compared to conventional energy storage devices, it is still restricted by the newly emerging issue of how to balance energy density and mechanical flexibility, which is closely relative to the specific manufacturing technology and ink process. Unfortunately, to date, research on the correlation between ink composition, device structure, capacitance, and the flexibility of supercapacitors remains rare. In this work, based on the model of activated carbon (AC) and screen-printing technology, the effects of ink formulation ratios, binder types (ethyecellulose (EC), poly(vinylidene fluoride) (PVDF), carboxymethocel (CMC), and polyacrylic latex (LA133)), dimensional characteristics of carbon-based conductive agents (acetylene black, one-dimensional carbon nanotube, two-dimensional graphene), and the thickness of screen-printing layers (1–10 layers) on the electrochemical energy storage performance and mechanical flexibility of the AFSCs are systematically studied. The results indicate that relative to the excellent flexible stability of the EC binder and large capacitance of the CMC binder, the ink with LA133 as the binder exhibits both superior capacitance and flexibility. Besides, the effectiveness of carbon-based conductive agents is that graphene is better than acetylene black, and acetylene black is much better than the carbon nanotube. When the ink composition comprises 85 wt % AC, 10 wt % acetylene black, and 5 wt % LA133, and 1–3 layers of inks are printed to fabricate the AFSCs, which display the most exceptional performance, including 91.12% of capacitance maintaining after 5000 bend–fold cycles. In contrast, for an excessively thick electrode with 10 layers of ink printing, only 19.30% of the initial capacitance is retained after the same flexible test cycle. These results illustrate the critical roles of screen-printing AFSCs from the ink process in obtaining high capacitance and flexible stability.