Green synthesis of MOF/CNT gels via in-situ physical mixing strategy toward quasi-solid-state Li-ion hybrid capacitor

Compositing metal-organic frameworks (MOFs) with carbon nanotubes (CNTs) can effectively improve their conductivity and structural instability to achieve excellent supercapacitor performance. However, the two main traditional composite strategies of ex-situ physical mixing and in-situ chemical growth still have some limitations, such as the heterogeneous dispersity and the destruction of CNTs, etc. In this work, we propose a green in-situ physical mixing method to construct advanced MIL-100-Fe/CNT architecture. An adding content of 10 % for CNTs results in the optimal composite structure within homogeneous dispersion and favorable interactions between MOF host and CNT guest, achieving a high specific capacitance of 431.6 F g−1 at the current density of 1 A g−1, which is much higher than of the pristine MOF (143.1 F g−1). An in-depth electrochemical study illustrates that the moderate addition of CNTs promotes the fast charge transfer dynamics of Li-ion in the composite electrode while the excessive CNTs will lead to localized aggregation and property degradation. A quasi-solid-state Li-ion hybrid capacitor device was assembled, displaying a high energy density of 20.2 W h kg−1 and a long cycle life of 89.4 % capacitance retention after 8000 cycles. The contribution has provided a new direction for constructing advanced MOF-based composite architectures for energy storage applications.