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Long Zhang, Fan Zhang, Xi Yang, Kai Leng, Yi Huang, and Yongsheng Chen* the capacitance of the supercapacitor is primarily dependent on the effective specific surface area (SSA) of electrode materials while the operating voltage is determined by the electrolytes/solvents.[2, 5, 7, 8] However, the commercially available ACs not only have poor SSA (< 2000 m 2 g− 1), but also the pore size is so small (mainly below 0.6 nm)[9] that the ions of IL electrolytes can’t access.[10] These will both lead to limited effective SSA of electrode materials in IL electrolytes which can offer high operating voltage. Furthermore, for the preparation of commercial ACs, some valuable materials such as coal, pitch and phenolic resin [1] are used as carbon sources and there is a significant carbon/material weight loss and serious toxic material releasing during the high temperature carbonization step, which caused waste of resources and environmental issues.

By viewing these, lot of efforts have been devoted on the preparation of ACs with high SSA and matched pore size in economical and environmentally friendly ways. Some cheap carbon sources such as seaweed and a series of starch were used as raw materials for ACs and good capacitance performance was achieved in the aqueous electrolytes.[11, 12] But the energy density still needs to be improved by further increasing SSA and operating voltage of electrolytes. Hydrothermal carbonization which could largely reduce the materials waste and releasing of toxic chemicals has been widely considered and used to replace the high temperature carbonization.[13–15] The products from combined process of …