Encapsulating transition metals or oxides in N-doped carbonaceous materials is a desirable strategy in the design of advanced energy materials in confined spaces. In this study, a core@shell structure of Co-Co3O4 core particles enclosed in a shell of carbon-nanotube (CNT)-incorporated nitrogen-doped carbon (hereafter abbreviated as Co-Co3O4@CNT-NC) was synthesized via simple pyrolysis of a melamine-formaldehyde (MF) resin and cobalt acetate composite in a N-2 atmosphere, followed by oxidation with H2O2. Because of the intimate contact between the Co-Co3O4 core particles and the graphitic shells, the obtained samples showed excellent performance. The as-prepared Co-Co3O4@CNT-NC structure exhibited improved electrical conductivity, which is suitable for an electrode material in electrochemical capacitors. It can deliver a high specific capacitance of 823.4 Fg(-1) at a current density of 1 Ag-1, as well as a capacitance retention of 93.6% after 10000 cycles. Moreover, an asymmetric two-cell supercapacitor composed of a Co-Co3O4@CNT-NC positive electrode and a reduced-graphene-oxide negative electrode exhibited a high energy density of 46.7 Wh kg(-1) at 1601.1 Wkg(-1). The easy preparation and high performance of the Co-Co3O4@CNT-NC composite make it an excellent material for supercapacitors application. (c) 2018 Elsevier Ltd. All rights reserved.