Crystal Facet-Engineered Anion Regulation Enables Fast-Charging Stability in Lithium Metal Batteries

Lithium metal batteries (LMBs) offer exceptional energy density and output voltage. However, their practical application remains hindered by sluggish ion transport and uncontrolled lithium dendrite formation, particularly under fast-charging conditions. Here, we report a facet-engineered anion-regulating separator based on zeolitic imidazolate framework-8 (ZIF-8) with preferentially crystal-exposed (110) facets. The coordinatively unsaturated Zn centers on this surface serve as Lewis acid sites that selectively anchor bis(trifluoromethanesulfonyl)imide anions (TFSI^-), inducing directional Li⁺ flux and suppressing dendritic growth. Concurrently, the microporous framework facilitates spatial lithium confinement, mitigating local current density and enhancing interfacial stability. As a result, the engineered separator enables ultra-stable cycling of Li||Cu cells for over 1400 cycles at 2 mA cm^-2 and 1 mAh cm^-2, delivering an average Coulombic efficiency of 98.7%. In full-cell configurations, LiFePO₄ (LFP) cells exhibit 99.9% Coulombic efficiency over 3000 cycles at 5 C, while high-loading Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811, 12.30 mg cm^-2) cell retains 84.4% of its capacity after 135 cycles. Furthermore, a Li||LFP pouch cell with a high cathode loading of 19.92 mg cm^-2 demonstrates robust cycling over 170 cycles. These findings establish facet-engineered separators based on framework materials as a versatile and scalable strategy for advancing stable and fast-charging metal batteries.