A battery-supercapacitor hybrid device composed of metallic zinc, a biodegradable ionic liquid electrolyte and graphite

Abstract

The integration of a battery-type electrode and of a capacitor-type electrode in a single device by proper design is an effective strategy in developing energy storage devices with high energy and power densities. Herein, we present a battery-supercapacitor hybrid device using metallic zinc as anode, a biodegradable ionic liquid (IL) as electrolyte, and graphite as cathode. The recently developed choline acetate ([Ch]OAc) biodegradable IL-based electrolyte enables reversible deposition/stripping of Zn(II). Spongy-like Zn with a high surface area is obtained, which allows fast charge/discharge at high rates. The adsorption/desorption of ions on the surface of the graphite cathode and intercalation/deintercalation of anions into/from the graphite layers occur at the graphite cathode. Raman spectra and X-ray photoelectron reveal the intercalation of IL into and the adsorption of IL on the graphite. Highly reversible adsorption/desorption of ions on the surface of the graphite electrodes in the [Ch]OAc-based electrolyte was demonstrated by a symmetric cell. The Zn/graphite hybrid device delivers an energy density of 53 Wh kg−1 at a power density of ~ 145 W kg−1 and 42 Wh kg−1 at ~ 400 W kg−1. The hybrid device also exhibits a long cycle life with ∼ 86% specific capacitance retained after 1000 cycles at a current density of 0.5 A g−1. The combination of well-available zinc, inexpensive graphite, and a biodegradable IL electrolyte in a cell could open new avenues for sustainable energy applications.