Robust metal-organic framework monoliths for long-term cycling lithium metal batteries

Lithium metal with low electrochemical potential and high theoretical capacity has attracted significant attention as an anode material for high-energy-density batteries. However, the practical application of Li metal anodes has been inhibited by the growth of Li dendrites during charge-discharge cycling. Nano- or micro-porous layers have been introduced at the Li/electrolyte interface to regulate the Li+ flux and stabilize the Li metal anode. However, such interlayers fabricated via slurry-casting have non-uniform porous structures containing interparticle voids due to the binders and solvents, which reduces the efficacy of the interlayer in suppressing dendritic Li growth. Herein, we report mechanically robust void-free metal-organic framework (MOF) monoliths that can effectively homogenize the Li+ flux and suppress dendritic growth. MOF monoliths (500 nm-thick) are directly grown on a polypropylene separator without binders via a simple chemical route with a void-free structure and mechanical robustness (Young's modulus of similar to 7.8 GPa). The monolithic MOF film facilitates the filtration of large anions through the nanopores, resulting in an increased Li+ transference number. Furthermore, electrochemical simulations and experiments confirm that MOF monoliths with well-ordered nanopores but without interparticle voids effectively redistribute the locally concentrated Li+ flux over the Li anode, leading to reversible Li plating and stripping. A Li metal battery (full cell) with MOF monoliths operates stably over 300 cycles with a capacity retention of 96.6%. The interlayer design proposed in this study offers the possibility of commercializing high-energy-density Li metal batteries with long cycle lifetimes. A monolithic MOF layer is synthesized on a porous separator via a simple chemical route, which effectively homogenizes the Li+ flux through its nanopores and physically blocks the growth of Li dendrites.