**4. Conclusions**

We have demonstrated a facile way for the synthesis of three-dimensional N-doped carbon nanotube flake structures by using linear PEI as catalytic template. The as-prepared N carbon materials exhibited high specific surface area, a stable interconnect nanotube network and 3D penetrable micro to macro scale hierarchical pores, which were beneficial for achieving high performance ELDSs. For nitrogen doped sample of *N*CNFs-1, ultra-high specific capacitances of 613 F g<sup>−</sup><sup>1</sup> at 1 A g<sup>−</sup><sup>1</sup> and 242 F g<sup>−</sup><sup>1</sup> at 10 A g<sup>−</sup>1, and excellent cycle ability with 95% retention over 20,000 cycles at 10 A g<sup>−</sup>1, was obtained, indicating the current processing is of grea<sup>t</sup> benefit for developing high performance electrodes for supercapacitors.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4991/9/9/1225/s1, Figure S1: The fitted high-resolution XPS spectrum of C 1s for the sample of *N*CNFs-1, Figure S2: The electrochemical performance of *N*CNFs-1 in a two-electrode system.

**Author Contributions:** D.X. and J.Q. contributed equally to this paper. Z.Z., Y.G. and X.L. designed the experiment. D.X., J.Q. and G.W. performed the experiments. L.Z. and S.Y. performed the electrochemical measurements. Z.Z., Y.G. and R.-h.J. designed the framework of the manuscript. D.X., J.Q., Z.Z., X.L., R.-h.J. and H.J. wrote the paper, D.C., Y.W. and Y.Z. provided some guidance for the experiment, and all authors participated in the discussion of the paper.

**Funding:** This study was supported in part by funding from the National Natural Science Foundation of China (NSFC, contract numbers: 51502268, 51325203 and 51574205), the Excellent Young Teacher Development Foundation of Zhengzhou University (contract cumber: 1421320050), and the Key Science and Technology Research Projects of Henan Provincial Education Department (contract number: 14B430023).

**Conflicts of Interest:** The authors declare no conflict of interest.
