Printing of a Passivation Layer for the Protection of Printed Supercapacitors

Manufacturing supercapacitors by printing enables reduced material waste, easy customization, adaptability of form factor with the application, and high compatibility with other printed electronics systems. Lifetime, durability, and stability are practical considerations to meet expectations besides the standard metrics of specific capacitance and energy and power densities. In this regard, passivation or encapsulation of the device is a critical aspect in all printed electronics but seldom considered. The passivation layer must be preferably printable instead of adopting conventional packaging technologies and therefore possess printable physical properties, not cause side reactions with other layers, and provide protection from the ambient. In this work, deterioration of unpassivated supercapacitors was analyzed first, and then a passivation method that satisfies the above requirements was developed. Several candidates for the passivation layer were tested, and their failure mechanisms were analyzed to identify a successful candidate, a UV-curable cycloaliphatic epoxy resin that was printed as the passivation layer by direct writing method on top of the functional layers of the supercapacitor. The supercapacitor with the resin passivation layer showed superior stability compared to the non-passivated device and provided as high performance as the manually passivated (wrapped in protective film) control device. Density functional theory calculations reveal the suitability of the resin to serve as a passivation material.