structural integrity upon mechanical deformation. In addition, thickness reduction is another challenging issue in the development of ceramic membranes. For these reasons, no meaningful results have been reported with ceramic membranes for battery separator applications.Among numerous architectural innovations of advanced materials, superlattice crystals, which are characterized with highly ordered/close-packed particle arrays, have been extensively investigated as a compelling building template in a wide variety of application fi elds such as photonic crystals, catalysts, electrodes, and sensors. [16][17][18] From the viewpoint of battery separator requirements, the close-packed particle arrays of superlattice crystals are expected to offer exceptional benefi ts for the thermal stability, dimensional rigidity and, more notably, porous structure (i.e., interstitial voids formed between the particles), although they are mechanically fragile upon external deformation stress.Considering again the key role [7][8][9] of battery separators as ion-conducting channels between electrodes, functional separators bearing chemical traps (that can capture unwanted heavy metal ions dissolved in liquid electrolyte) are expected to provide benefi cial effects on cell performance. For example, spinel lithium manganese oxide (LiMn 2 O 4 , LMO) materials, [ 19,20 ] which are widely used in large-scale batteries for applications in EVs and ESSs, are struggling with dissolution of Mn 2+ ions at elevated temperatures. The Mn 2+ dissolution-triggered disruption/contamination of electrodes are known to provoke capacity fading during charge/discharge cycling. Most of previous studies on this issue have been devoted to synthesis/ engineering of cathode materials, functional binders, and electrolytes. [21][22][23][24] Unfortunately, very few works, [ 25,26 ] which were simply focused on the surface modifi cation of polyethylene (PE) separators, were reported with battery separators.Here, intrigued by the abovementioned structural novelty/ potential benefi ts of ceramic membranes/superlattice crystals and also spurred by the urgent demand for chemical traps of heavy metal ions, we demonstrate a new class of ultimate battery separator based on fl exible/functional porous ceramic membranes (referred to as "2F ceramic separators") for highperformance lithium-ion batteries. The 2F ceramic separators are comprised of densely packed ceramic particles spatially besieged by electrospun nanofi ber skeleton. Both the ceramic particles and nanofi bers are rationally designed and synthesized to possess well-developed porous structure and also chemical functionality (as a new concept of chemical trap for chelating unwanted heavy metal ions dissolved in electrolytes). The compactly packed ceramic particles in the 2F separators, similar to the superlattice crystals, offer exceptional thermal stability/ dimensional rigidity and allow the formation of 3D-reticulated interstitial voids (that will be fi lled with liquid electrolyte). The