Hierarchical architecture of ZIF-8@ZIF-67-Derived N-doped carbon nanotube hollow polyhedron supported on 2D Ti3C2Tx nanosheets targeting enhanced lithium-ion capacitors

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The matching of long cycle life, high power density, and high energy density has been an inevitable requirement for the development of efficient anode materials for lithium-ion capacitors (LICs). Here, we introduce an N-doped carbon nanotube hollow polyhedron structure (Co3O4-CNT-800) with high specific surface area and active sites, which is anchored with two-dimensional (2D) Ti3C2Tx nanosheets with metallic conductivity and abundant surface functional groups by electrostatic adsorption to form a hierarchical multilevel hollow semi-covered framework structure. Benefiting from the synergistic effect between Co3O4-CNT-800 and Ti3C2Tx, the composites exhibit superior energy storage efficiency and long cycling stability. The Co3O4-CNT-800/Ti3C2Tx electrodes exhibit a high specific capacity of 817C/g at a current density of 0.5 A/g under the three-electrode system, and the capacity retention rate is 91 % after 5000 cycles at a current density of 2 A/g. Additionally, we assembled Co3O4-CNT-800/Ti3C2Tx as the anode and Activated carbon (AC) cathode to form LIC devices, which showed an electrochemical test result of 90.01 % capacitance retention after 8000 cycles at 2 A/g, and the maximum power density of the LIC was 3000 W/kg and the maximum energy density was 121 Wh/kg. This work pioneered the combination of N-doped carbon nanotube hollow polyhedron structure with two-dimensional Ti3C2Tx, which provides an effective strategy for preparing LIC negative electrode materials with high specific capacitance and long cycling stability.