Vertically Directed Ion Transport at the Molecular Scale in Composite Solid Electrolytes Enabled by Nanofiber-Confined Alignment of Single-Crystal MOF Tubes

The incorporation of a metal-organic framework, impregnated with ionic liquid (MOF@IL), into solid polymer electrolytes (SPE) is indeed a promising approach for advancing solid-state lithium batteries. However, the randomly distributed polycrystalline MOF particles inevitably lead to discontinuous and tortuous ion transport at the nano and molecular scales, drastically compromising the overall performance of these electrolytes. Herein, a composite solid electrolyte (CSE) incorporating vertically aligned single-crystal MOF@IL tubes (VMTSE) is developed by aligning the single-crystal MOF tubes along the same direction as that of the vertically aligned polyacrylonitrile (PAN) nanofibers. The PAN nanofiber substrate can confine and guide the continuous vertical alignment of MOF tubes to ensure the directed ion transport at the nanoscale. Meanwhile, compared to the long-range disordered pore structures in polycrystalline MOFs, the orientation of the one-dimensional (1D) channel pores within the single-crystal MOF tubes aligns with the tubular axis, thereby further enabling continuously directed ion transport at the molecular scale. As a result, the VMTSE exhibits a high ionic conductivity of 3.33 × 10^-3 S cm^-1 at 60 °C, and the corresponding LiFePO₄ || Li full battery achieves a stable discharge capacity of 101.04 mAh g^-1 with 78% capacity retention after 200 cycles at 1 C (60 °C). This work demonstrates the feasibility of precisely regulating Li⁺ transport pathways at multiscales by confining and guiding the directed arrangement of single-crystal MOF tubes within nanofibers to boost the performance of CSEs.