Magnesium fluoride-engineered UiO-66 artificial protection layers for dendrite-free lithium metal batteries

Abstract

Li metal is considered an ideal anode material for high-energy-density rechargeable Li metal batteries (LMBs). Nevertheless, sluggish Li⁺ transport kinetics and uncontrolled Li dendrite growth result in poor cycling performance, impeding its practical application. In this study, MgF₂-infiltrated UiO-66 nanoparticles (I-MgF₂@UiO) with F-terminated groups are developed as artificial protective layers for Li metal anodes. The fluorination of UiO-66-based metal–organic framework nanoparticles modifies their nanopores to allow the permeation of MgF₂. The F-terminated groups and infiltrated MgF₂ in the I-MgF₂@UiO electrode effectively facilitate the dissociation of the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and the desolvation of the solvated Li⁺ clusters, resulting in fast Li⁺ transport kinetics with a high Li⁺ transference number and ionic conductivity. Furthermore, lithiophilic Mg_xLi_y alloys and LiF-rich solid electrolyte interphase (SEI) that form on the Li metal during the Li plating/stripping process provide a homogeneous Li⁺ flux and suppress Li dendritic growth. Benefiting from the I-MgF₂@UiO artificial layer, full cells coupled with a LiFePO₄ cathode show a long lifespan of over 2000 cycles even at a high current rate of 10C. The findings provide new insights and a promising strategy for the practical application of high-energy-density LMBs.