Constructing an Anion-Braking Separator to Regulate Local Li+ Solvation Structure for Stabilizing Lithium Metal Batteries.

Abstract

Lithium metal batteries (LMBs) offer significant advantages in energy density and output voltage, but they are severely limited by uncontrollable Li dendrite formation resulting from uneven Li+ behaviors and high reactivity with potential co-solvent plating. Herein, to uniformly enhance the Li behaviors in desolvation and diffusion, the local Li+ solvation shell structure is optimized by constructing an anion-braking separator, hence dynamically reducing the self-amplifying behavior of dendrites. As a prototypal, two-dimensional lithiated-montmorillonite (LiMMT) is blade-coated on the commercial separator, where abundant -OH groups as Lewis acidic sites and electron acceptors could selectively adsorb corresponding FSI- anions, regulating the solvation shell structure and restricting their migration. Meanwhile, the weakened anion mobility delays the time of breaking electrical neutrality, and the Li nucleation density is quantified through the respective experimental, theoretical and spectroscopical results, providing a comprehensive understanding of modifying anion and cation behaviors on dendritic growth suppression. As anticipated, a long Li plating/stripping lifespan up to 1800 h and a significantly increased average Coulombic efficiency of 98.8% are achieved under 3.0 mAh cm-2. The fabricated high-loading Li-LFP or Li-NCM523 full-cells display the cycle durability with enhanced capacity retention of nearly 100%, providing the instructive guide towards realizing dendrite-free LMBs.