Synergistic effect of solvent addition and temperature treatment on conductivity enhancement of MWCNTs: PEDOT:PSS composite ink for electrodes in all printed solid-state micro-supercapacitors

All solid-state micro-supercapacitors (S-MSCs) are pivotal for modern wearables as they offer rapid energy storage and release, with seamless integration into small, lightweight wearables. Developing all printed S-MSCs is a cost-effective alternative to traditional S-MSCs and can potentially revolutionize wearable energy storage technologies. This manuscript presents an innovative, substrate-friendly approach to enhance the conductivity and electrochemical performance of screen-printed electrodes for S-MSCs using multi-walled carbon nanotubes (MWCNTs): PEDOT:PSS (poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate)) composite ink. By incorporating various polar solvents into the ink formulation and optimizing printing and drying parameters, a four-fold increase in conductivity (5.5 × 103 S/m) was achieved. The synergy of polar solvent addition and temperature treatment on the dielectric screening, preferential solvation, and partial segregation of PSS were identified as the principal reason behind this enhancement. The optimally formulated ink was employed to create supercapacitor electrodes, demonstrating hybrid capacitive behavior with both liquid and gel electrolytes. An impressive 97.5 % decrease in charge transfer resistance (RCT) and a corresponding increase in areal capacitance and energy density were observed for these supercapacitors due to the segregation of PEDOT and PSS achieved by the synergistic effect. All printed S-MSCs were also fabricated with an impressive areal capacitance of 9.82 mF/cm2 @ 60 µA/cm2 and areal energy density of 1.964 µWh/cm2 at an areal power density of 63 µW/cm2. The fabricated S-MSCs exhibited impeccable capacitance retention of 99.7 % after 6,000 operation cycles and impressive stability upto 10,000 bending cycles, making them promising energy storage solutions for flexible and wearable devices.