Tailored PolyMOFs for Ion Transport in Lithium-based Battery Electrolyte

Abstract

Solid-state electrolytes are a safer, more processable alternative to liquid organic electrolytes for energy storage applications. Metal-organic frameworks, with facile functional tunability and long-range order, have been implemented in a wide range of energy storage applications, including as solid state electrolyte materials. In this work, we investigate quasi-solid state electrolyte materials, combining the ionic transport properties of liquid electrolyte, polymers, and MOFs utilizing an electrolyte-loaded polymer/MOF composite material called polyMOFs. Herein, we demonstrate that the functionality of the polymer backbone of the polyMOF linker affects ion transport in the material. The poly(ethylene glycol) (PEG) based polyMOFs exhibit greater ionic conductivity, lithium transference number, and lower activation energy than its polyethylene (PE) counterpart. We propose these improvements are due to stronger coordination of Li+ to oxide sites in PEG, as seen through solid-sate 7Li nuclear magnetic resonance spectroscopy, allowing for dissociation of Li and its associated anion. DFT studies further reveal that the confined solvent molecule mediates Li⁺ transport in PEG-functionalized UiO-66 framework via a metastable adsorption and hopping mechanism. This work outlines the benefit of utilizing polymeric functionalization in quasi-solid state MOF electrolytes, opening the door for future materials at the interface of polymer and MOF for energy storage technologies.