The nanostructure design of porous carbon-based electrode materials is key to improving the electrochemical performance of supercapacitors. In this study, hierarchically porous carbon nanosheets (HP-CNSs) were fabricated using waste coffee grounds by in situ carbonization and activation processes using KOH. Despite the simple synthesis process, the HP-CNSs had a high aspect ratio nanostructure (∼20 nm thickness to several micrometers in lateral size), a high specific surface area of 1945.7 m(2) g(-1), numerous heteroatoms, and good electrical transport properties, as well as hierarchically porous characteristics (0.5-10 nm in size). HP-CNS-based supercapacitors showed a specific energy of 35.4 Wh kg(-1) at 11250 W kg(-1) and of 23 Wh kg(-1) for a 3 s charge/discharge current rate corresponding to a specific power of 30000 W kg(-1). Additionally, the HP-CNS supercapacitors demonstrated good cyclic performance over 5000 cycles.

Intercalation-based anode materials for Na-ion batteries show relatively unfavorable electrochemical performances compared with those of Li-ion batteries because of the larger and heavier Na ion, as well as its higher electrode potential. In contrast, conversion-reaction-based anode materials have great potential for use in Na-ion batteries. In this study, copper sulfide nanodisks (CuS-NDs) were fabricated by a simple low-temperature reaction and applied as the anode materials for Na-ion batteries with acid-treated single-walled carbon nanotubes (a-SWCNTs), which act as a paperlike nanohybrid. The nanohybrids had a high reversible capacity of ca. 610 mA h g–1 and high rate capabilities at current rates from 0.1 to 3 A g–1 during the conversion reaction that reversibly forms Na2S and Cu metal. In addition, their electrochemical performances were stable and were maintained over 500 repetitive cycles; this stability arises from the unique nanohybrid structure, in which CuS-NDs are bound together by the a-SWCNT network.

No abstract

No abstract

No abstract