Meso-pore dominant activated carbon from spent coffee grounds for high-performance electrochemical capacitors in organic electrolyte

Abstract

Conventionally, conductive additives and metallic current collectors are two major decisive factors to determine the electrochemical performances of electrode materials in supercapacitors (SCs). Without those, most reported materials for SCs are far beyond the standard performances. Herein, we develop a pore-size tunable and highly-pure nanosheet-like activated carbon (AC) form spent coffee grounds (SCGs) with high specific-surface-area (2497 m2 g−1) and large pore volume (1.28 cm3 g−1). The meso-pore/total-pore volume proportions (r) of the as-prepared samples, AC1200 (r = 10.25%), AC1800 (r = 20.10%), and AC2500 (67.34%), are simply adjusted at desired temperatures (750–900 ºC) using physical activation with CO2. The SCG-based electrodes for symmetric electric double-layer capacitors (EDLC) were prepared using free-standing carbon films on cellulose separator, not on Al or Cu foils, without adding any conductive additives. Interestingly, the AC2500-based electrode, a narrow mesopore-rich (mainly 2–4 nm) AC, presents superior capacitance of 222.4 F g−1 at 0.5 A g−1 in 1.5 M LiClO4/propylene carbonate. The capacitance is superior to those of micropore-rich samples (AC1200 and AC1800) including of two commercial products (YP-50 and ACS20). Furthermore, the AC2500-based EDLC exhibits a remarkable energy density of 48.3 Wh kg−1 at 627 W kg−1, and maintains a high energy density of 33.8 Wh kg−1 at 3733 W kg−1. In present work, we demonstrate that narrow meso-pore (2–4 nm) dominant and nanosheet-like carbons would conduct high-performance electrochemical behaviors without the assistance of conductive additives. Moreover, we provide a promising preparation route for pore-size-tunable ACs from bio-mass wastes with remarkable performance for energy storage applications.