Low-leakage-current deep eutectic solvent based supercapacitor for disposable, flexible, and ultra-low-power electronics

Alcohol-based deep eutectic solvents (DESs), exhibiting energy/power densities of 12–14 Wh kg⁻¹ / 6.5–7.5 kW kg⁻¹ with YP-80F activated carbon at 1.8 V cell voltage, are demonstrated as efficient low-leakage-current electrolytes suitable for ultra-low-power printed energy storage. Through low faradaic self-discharge and charge redistribution contributions, they provide significant (p < 0.002) suppression of specific leakage current vs. Reline-DES (−28–40% at 1.8 V/cell) and aqueous (−22–28% at 1.2 V/cell) electrolytes in printed supercapacitor cells. A sustainable DES based on choline chloride and propylene glycol demonstrates the lowest average capacitance-normalised leakage current of 103 μA F⁻¹ at 1.8 V and 44 μA F⁻¹ at 1.2 V post 1-h constant-voltage charging, a two-electrode gravimetric capacitance of 27 F g⁻¹ at 0.5 mA cm⁻² with 18%/82% diffusive/non-diffusive charge storage contributions, 94% capacitance retention post 10,000 charge-discharge cycles, and > 98% coulombic efficiency at 0.5–5 mA cm⁻² current densities. Flexible 3.6 V supercapacitor modules with a non-toxic and disposable material stack are fabricated using screen-printing technique; 33 mm × 30 mm modules with 1× and 2× printed electrode layers provide capacitances / leakage currents of 120 mF / 18 μA and 200 mF / 37 μA respectively, with high integrability and stable capacitive performance under 90°/180° bending conditions, offering a practical low-cost energy storage solution for disposable/single-use printed electronics.