A planar supercapacitor made of supramolecular nanofibre based solid electrolyte exhibiting 8 V window

Abstract

Planar microsupercapacitors are emerging as essential devices for rapid energy sourcing in on-chip circuitry. A serious limitation in comparison to planar microbatteries is the energy density that a planar supercapacitor can offer (∼two orders less), which in turn relates to the maximum working potential of the electrolyte used in it, which is typically below 3 V. In this article, we report the fabrication of a planar supercapacitor with an operating voltage window, highest among the reported till date. The electrolyte used is essentially a solid in the form of nanofibres of a supramolecular donor-acceptor assembly, consisting of coronene tetracarboxylate salt (CS) and dodecyl methyl viologen (DMV), carrying positive (K+) and negative (Br−) ionic charges, respectively. The fibres are drop-spread across Ti microgap electrodes and the device is operated in the ambient or in a humidity-controlled cell. The device is found stable up to a working potential window of 8 V, exhibiting areal capacitance values of 0.2 mF/cm2 under room humidity conditions (RH, 65%) which was enhanced to 9.5 mF/cm2 under 90% RH in presence of hygroscopic KBr crystallites. The estimated areal energy and power density values are remarkable, 85 μWh cm−2 and 24.7 W cm−2 respectively. The device retained 86% capacitance even after 50000 charge-discharge cycles. Using a single device, AC line filtering is shown possible with ripple less than 5%. These extraordinary properties are borne out of the facile diffusion of ions along the 1D face-to-face arrangement of the D-A molecules in the nanofibres while the ambient oxide covered Ti surface providing the required electrochemical stability to the device.