Carbon nanotube-confined NiCoLDH heterostructures for ultrahigh stable supercapacitors

The structural instability of metal oxides retards realizing high-performance and long lifespan supercapacitors. We prepare an electrochemical active heterostructure of NiCo layered double hydroxide (LDH) confined by carboxyl carbon nanotube (CNTCOOH). Through the electrostatic interactions between carboxyl groups (COO−) of CNTCOOH and metal cations of LDH under a simple hydrothermal treatment, the CNTCOOH confined NiCoLDH (CNTCOOH-c-NiCoLDH) can be easily fabricated. The CNTCOOH-c-NiCoLDH demonstrates the specific morphology of rope-fastened plates and shows ultrahigh cycled stability. In addition, the hydrophilic carboxyl groups on CNTCOOH also regulates the interfacial electronic coupling and electrolyte soaking, resulting in high rate capability. The charge-storage capacitance of CNTCOOH-c-NiCoLDH heterostructures reaches 2120.8 F/g at 1 A/g. The devices of CNTCOOH-c-NiCoLDH//AC show both high energy density (171.0 Wh/kg) and high power density (950.0 W/kg), and have ultrahigh capacity retention rate of 93.64 % after 50,000 charge and discharge cycles at a high current density of 5 A/g. This work supports an effective confinement idea and a facile method that can be applied on a large scale for the design and fabrication of super high stable metal oxide-based supercapacitors.