Fabrication of High-Performance All-Solid-State Asymmetric Supercapacitors Based on Stable α-MnO2@NiCo2O4 Core–Shell Heterostructure and 3D-Nanocage N-Doped Porous Carbon

Abstract

A stable α-MnO2 nanowire@NiCo2O4 nanosheet core–shell heterostructure and a 3D-nanocage N-doped porous carbon nanosheet with high electrical conductivity are synthesized by a two-solution phase reaction and a facile one-step self-template technique, respectively. The unique α-MnO2@NiCo2O4 heterostructure is characterized by a stable nanostructure, fast electron transport, and numerous ion diffusion channels. The electrode exhibits a high specific capacitance of 1101 F g–1, and a cycling stability of 95.8% after 10 000 cycles. Moreover, by introducing N atoms which is favorable for rate performance, the 3D porous carbon offers a large surface area, a proper pore structure and especially high electron conductivity. The specific capacitance of the 3D N-doped porous nanocage carbon electrode reaches 100 F g–1 at a current densities as high as 100 A g–1. The all-solid-state symmetric supercapacitor with excellent electrochemical properties is fabricated using the α-MnO2@NiCo2O4 core–shell heterostructure as positive electrode, a 3D N-doped porous nanocage carbon as negative electrode, and a PAAK/KOH gel as solid-state electrolyte. The supercapacitor demonstrates an expanded working potential of 1.7 V, a maximum energy density of 46.2 Wh kg–1, a maximum power density of 15.3 kW kg–1, and good capacitance retention of 90% after 2000 cycles.