Fig. 5: Supercapacitor performance.

A Coulombic efficiency and areal capacity versus charge-discharge cycles, as a function of n/p ratios. The retention percentages are calculated after 50,000 cycles. B Specific energy versus specific power of our supercapacitor (n/p = 2.5), over a wide range of temperatures. C Photograph of a large 25.8 F supercapacitor (dimension: 4 cm × 5.5 cm). For part A, device with n/p = 4: 1.12 mg cm⁻² active carbon on carbon cloth as cathode; Cu current collector with CuNPs sputtered at 100 W as anode current collector; 1.41 mg cm⁻² active Zn amount; and 200 µL 15 M ZnCl₂ as electrolyte. Device with n/p = 2.5: 3.26 mg cm⁻² active carbon on carbon cloth as cathode; Cu current collector with CuNPs sputtered at 100 W as anode current collector; 2.54 mg cm⁻² active Zn amount; and 200 µL 15 M ZnCl₂ as electrolyte. For part B, device with n/p = 2.5: 1.25 mg cm⁻² active carbon on carbon cloth as cathode; Cu current collector with CuNPs sputtered at 100 W as anode current collector; 1.59 mg cm⁻² active Zn amount; and 200 µL 7.5 M ZnCl₂ as electrolyte. For part C, device with n/p = 2.5: 3.5 mg cm⁻² active carbon on carbon cloth as cathode; Cu current collector with CuNPs sputtered at 100 W as anode current collector; 2.69 mg cm⁻² active Zn amount; and 200 µL 15 M ZnCl₂ as electrolyte.