Enhancing High Voltage Stability via Fluorination of Functionalized Metal Organic Framework Electrolyte in Lithium Metal Batteries

The electrolyte stability under high-voltage conditions considerably limits the upper cut-off potential of solid-state electrolytes (SSEs) and therefore the energy density of all-solid-state batteries (ASSBs). In this work, metal-organic frameworks (MOFs) were fluorinated to lower the energy level of HOMO orbital and allow access to a 4F-MOF that exhibit enhanced anodic stability. The composited 4F-MOF/PEO electrolyte could not only transport Li+ ions in the ordered framework channels, but also provide a remarkable high-voltage stability up to 5.0 V, shielding oxidative decomposition that would otherwise occur at around 3.9 V for conventional PEO electrolytes. In addition, stable lithium deposition was demonstrated for more than 1,300 hours at 0.1 mA·cm-2, while reversible charge-discharge cycling performance was delivered in assembled Li||LiNi0.5Mn1.5O4 (LNMO) ASSBs up to 5.0 V. Post-mortem X-ray photoelectron spectroscopy (XPS) investigation on cathodes revealed presence of a LiF-rich cathode electrolyte interface (CEI), supporting promoted stability towards high-voltage ASSBs.