Gel Metal–Organic Frameworks in Highly Concentrated Electrolyte Promote Stable Solid-Electrolyte Interface on Lithium Metal Anodes

Highly concentrated electrolytes (HCEs) have been shown to hinder dendrite formation and improve cyclability in Li-based batteries. Herein, we developed a novel strategy to use an electrolyte matrix composed of gel metal-organic frameworks (g-MOFs) and an HCE consisting of 4.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in acetonitrile. The addition of Zr-based g-MOFs into the HCE creates a "sandy-slurry" electrolyte with higher ion conductivity and Li⁺ transference number (i.e., g-MOF-808: σ = 16.0 mS cm⁻¹, tLi+ = 0.800) compared to the HCE alone (σ = 8.52 mS cm⁻², tLi+ = 0.511). Li-symmetric cells containing g-MOF electrolyte have stable symmetric cell cycling at high charge/discharge rates. X-ray photoelectron spectroscopy and scanning electron microscopy show that the g-MOF changes the composition of the solid-electrolyte interface of the Li electrode compared with control samples. In a series of Zr g-MOFs with varying porosity, we discovered that cells containing g-MOF-808 can be symmetrically cycled with low overpotential values compared to the control Li-symmetric cells under similar conditions. To the best of our knowledge, this study is the first to implement g-MOFs in Li-based batteries and demonstrates the potential of porous framework materials as gel electrolyte components for high-density energy storage devices.