In this study, the internal resistance with the increasing of electrode thickness in a typical nanoporous carbon-based supercapacitor and their corresponding electrochemical performances were designed and investigated in detail. As for the carbon-based double electrode layer electrochemical system, electrochemical experiments greatly support the fact of nonlinear dependence and indicate that the curve of internal resistance vs. electrode thickness can have a minimum value when the thickness increasing from 10 to 140 μm. To explain the underlying mechanisms responsible for the nonlinear dependence, a theoretical model based on a porous electrode/electrolyte electrochemical system was proposed. As expected, the results of calculations carried out in the framework of the proposed model can be very good agreement with the experimental data. According to the calculation, the optimized electrode thickness is 53.1 μm corresponding to the minimum value of SC internal resistance. Obviously, the current research results might greatly support the nonlinear conclusion instead of linear relationship between the internal resistance and the electrode thickness and may shed some light on the fabrication and exploration of supercapacitors with high power density.

The existence of supercapacitors with a long calendar life, a superior power density, and a higher mechanical stability is increasingly drawing attention due to their viability to be used as power sources onboard wearable electronics. However, a considerable issue is that upon repeated cycling, an unstable interface between the conducting substrate and the active materials leads to low conductivity and overall poor device performance, thereby hindering its practical applications. Tantalum foil is a potential substrate which can be used in the fabrication of supercapacitors; it has strong corrosion resistive properties, good bendability, and is mechanically stable. These properties make it suitable for use in supercapacitors. Here, a printable tantalum foil substrate with printed carbon particles on its surface is described, showing high adhesion and a greatly improved interface for the fabrication of traditional activated carbon film based supercapacitors. The flexible solid‐state supercapacitors with this printable substrate achieve a higher volumetric capacitance, outstanding energy density, a higher power density, and provide excellent mechanical flexibility. These results indicate that the strategy to use a printable substrate with an enhanced adhesion interface provides an alternative method to achieve highly stable and highly efficient supercapacitors which are ideal to be used in portable devices and flexible electronics.