Fig. 1: Strategies to raise the gravimetric capacity of zinc ion supercapacitors.

It is desirable to balance the n/p ratio towards 1. To decrease the reliance on excessive zinc in the “n” part of the ratio, copper nanoparticles are deposited on the current collector to favor electro-crystallization of Zn(002) which increases Coulombic efficiency and extends cycle life. For the “p” component, the cathode capacity is enhanced by an activation method based on gas evolution that cracks additional pores in the activated carbon electrode. The calculations used for the device capacity plot are detailed in the “Methods section”.