**Linear-Polyethyleneimine-Templated Synthesis of N-Doped Carbon Nanonet Flakes for High-performance Supercapacitor Electrodes**

**Dengchao Xia 1, Junpeng Quan 1, Guodong Wu 1, Xinling Liu 2, Zongtao Zhang 1,\*, Haipeng Ji 1, Deliang Chen 1, Liying Zhang 1, Yu Wang 1, Shasha Yi 1, Ying Zhou 1, Yanfeng Gao 1,3,\* and Ren-hua Jin 4,\***


Received: 28 July 2019; Accepted: 26 August 2019; Published: 29 August 2019

**Abstract:** Novel N-doped carbon nanonet flakes (*N*CNFs), consisting of three-dimensional interconnected carbon nanotube and penetrable mesopore channels were synthesized in the assistance of a hybrid catalytic template of silica-coated-linear polyethyleneimine (PEI). Resorcinol-formaldehyde resin and melamine were used as precursors for carbon and nitrogen, respectively, which were spontaneously formed on the silica-coated-PEI template and then annealed at 700 ◦C in a N2 atmosphere to be transformed into the hierarchical 3D N-doped carbon nanonetworks. The obtained *N*CNFs possess high surface area (946 m<sup>2</sup> g<sup>−</sup>1), uniform pore size (2–5 nm), and excellent electron and ion conductivity, which were quite beneficial for electrochemical double-layered supercapacitors (EDLSs). The supercapacitor synthesized from *N*CNFs electrodes exhibited both extremely high capacitance (up to 613 F g<sup>−</sup><sup>1</sup> at 1 A g<sup>−</sup>1) and excellent long-term capacitance retention performance (96% capacitive retention after 20,000 cycles), which established the current processing among the most competitive strategies for the synthesis of high performance supercapacitors.

**Keywords:** linear PEI; N-doped carbon nanonet flask (*N*CNFs); template-assisted synthesis; electrochemical properties; supercapacitor
