Ion-conductive metal-organic framework membranes for lithium metal batteries Rui Tan 1 , Anqi Wang 1 , Zhiyu Fan 1 , Thomas D. Bennett 2 , Qilei Song 1 1 Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK, 2 Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Rd, Cambridge, CB3 0FS, UK Lithium-ion batteries (LIBs) have been widely used for transport and grid-scale energy storage, however, they are reaching the limit of energy density and facing the safety issue for large-scale applications due to the use of flammable organic liquid electrolytes1. Solid-state batteries (SSBs) hold great promise for replacing conventional LIBs due to their higher energy density and enhanced safety2. Current inorganic and organic solid electrolytes possess low ionic conductivity and there are various technical challenges, e.g., poor chemical stability, dendrite growth, or difficulty of manufacturing at large scale. Metal-organic frameworks (MOFs) have great potential for applications as next-generation ion-conductive membrane separators for battery devices owing to their structural functionality, pore size, adjustable surface chemistry and physical stability3. The versatile coordination chemistry allows the elegant tuning of pore structures and functional groups to create fast ion transport channels so as to improve the overall ionic conductivity and lithium-ion transference number. However, the ion transport in crystalline MOFs are usually limited by the grain boundaries and it remains challenging to shape MOFs crystals into large-size and grain boundary-free electrolyte membranes. In recent years, amorphous MOFs and MOF glasses have emerged as promising new class of MOF materials and showed potential for molecular separations and energy storage devices where selective molecular and ion transport critically determines their performance4. Here we report a novel approach to prepare MOF materials into monolithic membranes that enable high ionic conductivity (>10-3 S/cm) as well as high lithium-ion transference number5. The structures of the MOF membranes critically determine the ion transport properties and battery performance. The MOF membranes enable the uniform stripping/plating of Li ions owing to uniform transport in nanoscale pores. The MOF membrane was assembled into tangible cells and demonstrated promising performance. The strategy of processing MOF membranes and the structure-property-function relationships will inspire design of next-generation of ion-selective membranes with fast ion-conducting channels for applications in a variety of electrochemical devices. References 1. Jürgen Janek and Wolfgang G. Zeier, Nature Energy, DOI: 10.1038/NENERGY.2016.141. 2. Zhao, et al, Nature Reviews Materials, 5, 229–252 (2020). 3. S. Bai et al. Nature Energy 1, 16094, 2016 4. TD Bennett, AK Cheetham. Accounts of chemical research 47 (5), 1555-1562 (2014). 5. Tan et al, under review.
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