Cork-Derived Carbon Sheets for High-Performance Na-Ion Capacitors
M.D. Casal, Noel Díez, Sara Payá, Marta Sevilla
Abstract
High Resolution Image Download MS PowerPoint Slide S-doped carbon sheets have been easily prepared by deconstructing the 3D cellular structure of a fully sustainable and renewable biomass material such as cork through a mild ball-milling process. S-doping of the material (>14 wt % S) has been achieved by using sulfur as an earth-abundant, cost-effective, and environmentally benign S-dopant. Such synthesized materials provide large Na storage capacities in the range of 300–550 mAh g –1 at 0.1 A g –1 and can handle large current densities of 10 A g –1, providing 55–140 mAh g –1 . Their increased packing density compared to the 3D pristine structure allows them to also provide good volumetric capacities in the range of 285–522 mAh cm –3 at 0.1 A g –1 and 53–133 mAh cm –3 at 10 A g –1 . In addition, highly porous carbon sheets ( S BET > 2700 m 2 g –1 ) have been produced from the same carbon precursor by rationally designing the chemical activation approach. These materials are able to provide good anion storage capacities/capacitances of up to 100–114 mAh g –1 /163–196 F g –1 . A sodium-ion capacitor assembled with the optimized S-doped carbon sheets and the highly porous carbon sheets with mass matching ratios provided the best energy/power characteristics (90 Wh kg –1 at 29 kW kg –1 ) in combination with robust cycling stability over 10,000 cycles, with a capacity fade of only 0.0018% per cycle.