Using a coating layer to modify the separator in a practical Li metal battery has attracted wide attention; however, its function on Li-ion diffusion and Li plating/stripping has not been systematically investigated. Herein, in situ electrochemical Raman characterization using modified coin cell configuration is employed to directly reveal the anion adsorption mechanism of the coating layer. The adsorption ability of the MOF-based coating layer on the commercial separator is able to preserve high concentration of anions near the electrolyte/Li interface, which generates high local Li-ion concentration that delays the drain of Li+ to uniform Li plating. The feasible and large-area fabrication of GO/ZIF-8-modified separator enables the assembly of pouch cell strictly following practical parameters. 0.4 Ah pouch cell (Li/NCM811) delivers stable capacity for over 100 cycles. The deep understanding of the mechanism of how a coating layer affects Li plating behavior is helpful for the designing and preparation of high-performance separators for Li metal batteries.
Keywords: Li-ions concentration; in situ characterization; lithium metal battery; metal organic framework; separator.