Metal organic frameworks (MOFs) have unique advantages in optimizing the ionic conductivity of battery separators because of their rich cavity structure and highly ordered and connected pores. In this study, we used a hydrothermal method to synthesize a functional material, Ag-MOF crystal, as a separator coating content, and then studied the properties and application effect of the MOF-Al2O3-blended coating applying to a polyethylene (PE) separator (MOFxAl1-x/PE). Results show that MOF0.08Al0.92/PE (MOF/Al2O3 = 0.08:0.92) used in NCM811||Li cells significantly not only improves the fast charge-discharge performance of the cells but also inhibits the growth of lithium dendrites during long-term charge-discharge cycling; the Li+ transference number (tLi+) of the MOF0.08Al0.92/PE composite separator is 0.61; the Li||separator||Li half-cell circulates stably for 1000 h at varying current density from 0.5 to 10 mA cm-2 and only produces low overpotentials, indicating that MOF0.08Al0.92 stabilizes lithium. The initial capacity of the NCM811||Li cell using the MOF0.08Al0.92/PE separator is 165.0 mA h g-1, its capacity retention is 70.67% after 300 cycles at 5 C, and the interface resistance of the cells only increases from 13.8 to 31.5 Ω, whereas the capacity retention of Al2O3/PE separator batteries is only 40.41% (62.2 mA h g-1) under the same conditions. During the charge-discharge cycling, the MOF-Al2O3 coating induces the lithium anode to quickly form a stable and dense solid-electrolyte interphase layer, promotes the uniform deposition of Li+, and inhibits the growth of lithium dendrites as well.
Keywords: Ag-MOF; MOF-Al2O3 coating; NCM811||Li; fast charge; functional separators; lithium dendrites; stable SEI.