Extraordinary Ionic Conductivity Excited by Hierarchical Ion-Transport Pathways in MOF-Based Quasi-Solid Electrolytes.

Abstract

Liquid-electrolyte-laden metal-organic frameworks (LE-laden MOFs) are promising quasi-solid electrolytes (QSEs) for metal-anode batteries. To achieve a high ionic conductivity, considerable efforts have been devoted to designing continuous and compact LE-laden MOF layers. Surprisingly, in this work, an extraordinarily high ionic conductivity (1.02 mS cm^-1 ) is observed in an LE-laden MOF electrolyte with abundant interstices and cracks. Herein, various macroscopic and mesoscopic pore structures of Li-LE-laden HKUST-1 QSEs are prepared via morphology control and different cold-pressing procedures. Thereinto, Li-LE-laden cuboctahedron HKUST-1 prepared under 150 MPa cold-pressing with an optimal hierarchical pore structure (Li-Cuboct-H) exhibits the highest ambient ionic conductivity (1.02 mS cm^-1 ). It is found that interstices and cracks in electrolytes construct a set of interconnected Li-LE networks with innate MOF channels and facilitate Li⁺ transfer in the hybrid ion-transport pathways. The Li/LiFePO₄ cells based on Li-Cuboct-H deliver a splendid capacity retention of 93% over 210 cycles at 1 C. Meanwhile, the high ionic conductivities (higher than 10^-4 S cm^-1 ) can be achieved in different ion conductor systems (Na, Mg, and Al) under the same guideline. This work redefines the understanding of ion transport in MOF-based QSEs and breaks the bottleneck of MOF-based QSEs.