Solvothermal modification of activated carbon for enhanced electrochemical performance in screen-printed supercapacitors

This study reports a novel method for enhancing the specific capacitance of screen-printed, activated-carbon-based supercapacitor electrodes through solvothermal modification of the active material. Commercial activated carbon (Kuraray YP-80F) is suspended in N,N-Dimethylformamide (DMF) and heat treated in a sealed autoclave at 160 °C for 12 h to modify its hydrophilicity and surface properties, eliminating the need for an additional drying retardant in the aqueous electrode ink that limits its electrochemically active surface area. Additionally, the average pore volume of the carbon material is increased by 50 % (1.22 cm 3 g -1 to 1.83 cm 3 g -1 ) and the specific surface area by 21 % (2040 m 2 g −1 to 2471 m 2 g −1 ), resulting in further enhanced double layer formation. Screen-printed two-electrode supercapacitors demonstrate a specific capacitance increase of ∼140 % (12 F g −1 to 28 F g −1 ) with aqueous electrolyte, and ∼80 % (18 F g −1 to 33 F g −1 ) with deep eutectic solvent (DES) electrolyte, compared to cells fabricated using a commercial drying retardant. Moreover, similar capacitance retention after 10,000 charge-discharge cycles (∼95 % with aqueous, ∼85 % with DES), and a 22–25 % reduction in capacitance-normalised leakage current (40 μA F −1 to 30 μA F −1 with aqueous, 145 μA F −1 to 113 μA F −1 with DES) is obtained using solvothermal treatment. • DMF is incorporated within YP-80F activated carbon using solvothermal treatment. • Treatment improves hydrophilicity, ink stability, and active surface area. • Specific capacitance is increased by 80 % (DES)/140 % (aqueous). • Solvothermal modification does not impact cyclic stability.