Porous Carbon Nanosheets Derived from Spent Coffee Grounds for Highly Stable Electric Double-Layer Capacitors Enabled by Structurally Complementary Carbons

Abstract

Despite the fact that porous carbons are the primary components of electric double-layer capacitors (EDLC), conductive additives have typically been necessary to aid in the establishment of improved conductive pathways. In this study, we use two-dimensional porous carbon sheets (2D PCNs) derived from spent coffee grounds as the active component and integrated them with two structurally complementary carbon blacks (CB)-BP2000 and Super P to compose a highly stable EDLC electrode in an organic electrolyte. The carbon electrode with the best mass ratio is AC2500/BP2000/Super P = 100/15/5 (AC25-BP75SP25) and was prepared using a suction-filtration method on a cellulose separator rather than direct coating on a metallic foil. The specific capacitance of AC25-BP75SP25-based EDLCs in 1 M TEABF 4 /propylene carbonate is as high as 226.8 F g −1 at 0.5 A g −1 . Furthermore, the cycling tests show a specific capacitance of 194.6 F g −1 at 5 A g −1 with a high-voltage window of 2.5−2.7 V and a Coulombic efficiency near 98 % after 50,000 cycles. The value is remarkably stable when compared with the AC2500-based electrode without conductive CB or adding only one kind of CB. The energy density can reach a high level of 56.7 Wh kg −1 @ 750 W kg −1 and 42.8 Wh kg −1 @ 11.8 kW kg −1 , indicating that the assembled EDLC can maintain a high energy density when operated under harsh charge−discharge conditions. Our findings could provide a new strategy to practically utilize carbon-electrode materials derived from biomass wastes for high-performance EDLC.