Hierarchical porous CNTs@NCS@MnO2 composites: rational design and high asymmetric supercapacitor performance

Abstract

In this contribution, we present a novel and rational strategy for preparing hierarchical porous CNTs@NCS@MnO₂ core–shell composites via a facile in situ chemical polymerization coating method, followed by a hydrothermal process. An intermediate nitrogen-doped carbon shell (NCS) with mesoporous structure and favorable chemical durability is obtained by utilizing resorcinol–formaldehyde resin as the carbon source and L-cysteine as the nitrogen source. Benefiting from a unique structure and considerable combination, the composites exhibit a highly comprehensive electrochemical performance: high specific capacitance (312.5 F g⁻¹ at a current density of 1 A g⁻¹), good rate capability (76.8% retention with the charge–discharge rate increasing from 1 A g⁻¹ to 10 A g⁻¹), superior reversibility and cycling stability (92.7% capacitance retention after 4000 cycles at 8 A g⁻¹). In order to increase the energy density and voltage window, an asymmetric supercapacitor (ASC) was assembled using CNTs@NCS@MnO₂ and activated carbon (AC) as the positive and negative electrodes, respectively. The as-fabricated asymmetric supercapacitor achieved a high specific capacitance with a stable operating voltage of 1.8 V and a maximum energy density of 27.3 W h kg⁻¹. Such a synthetic route to prepare capacitor materials can thoroughly motivate the synergistic effect between electrical double layer capacitors and pseudocapacitors for obtaining high comprehensive performance electrodes in energy storage fields.