A universal KOH-free strategy towards nitrogen-doped carbon nanosheets for high-rate and high-energy storage devices†
In this work, we report a universal KOH-free strategy to fabricate two-dimensional nitrogen-doped carbon nanosheets from edible oil residues. The saponification process and novel mild activators are introduced for the first time to optimize the microstructure of the nitrogen-doped carbon nanosheets. The resulting carbon nanosheets present a high specific surface area (2470 m2 g−1), wide pore size distribution (0.5–60 nm), and high nitrogen content (4.96%). As electrode materials for supercapacitors, the as-prepared nitrogen-doped carbon nanosheets exhibit a high specific capacitance of 340 F g−1 at a current density of 0.5 A g−1 and retain a high capacitance of 282 F g−1 at a very high current density of 50 A g−1, with no capacitance attenuation seen after 20 000 charge/discharge cycles in 6.0 M KOH electrolyte. The as-fabricated carbon nanosheet-based symmetric cell manifests a maximum energy density of 55.5 W h kg−1 at the power density of 369 W kg−1 and retains a high energy density of 32.3 W h kg−1 at 6180 W kg−1 in 1.0 M LiPF6 electrolyte. Experimental results reveal that this study provides an efficient and universal strategy for novel pre-treatment and KOH-free activation of nitrogen-doped carbon nanosheets with high specific surface area for high-rate and high-energy supercapacitors.