and the undesired soluble LiPSs migrate through the porous commercial separators to the metallic Li anode, causing corrosion and passivation. [8] In terms of the metallic Li anode, the Li-dendrite growth triggered by the nonuniform Li dissolution/deposition will induce an internal short circuit. [9] To counteract these negative consequences, researchers have developed hosts for sulfur encapsulation in cathode, [10][11][12][13] lithium anode protection, [14] and separator modification to prevent lithium polysulfides (LiPSs) from shuttling. [15][16][17] Proposing a rational design strategy for simultaneous enhancement of both metallic Li anode and sulfur cathode is of great significance. The separator, one of the most indispensable components, contacts both the cathode and anode directly. It is considered to be a facile and effective approach to functionalizing separators to confine LiPSs and synchronously regulate the Li dissolution/deposition in LSBs. [18][19][20] The commercial polyolefin separator with a low melting point and nonpolar characteristics results in poor electrolyte affinity and difficulty in modification. [21,22] In addition, most of the functionalization strategies have not paid attention to the thickness and weight, which would apparently reduce the energy density of LSBs.What's worse, the stripping of the coated layer from the separator extensively exists in traditional separator modification methods, which would significantly diminish practical performance and even raise serious safety concerns about Li-metal batteries. [23,24] Especially for high energy-density batteries used in electric vehicles (Tesla, 4680), a large amount of binder (polyvinylidene fluoride; PVDF) would be coated on the separator to improve cycle stability, preventing the powder from falling off during cycling, but this is still ineffective. [25,26] Magnetron sputtering, an effective approach for fiber functionalization, could be a solution to the aforementioned issues. [27] During the sputtering process, the functional target material would deposit on the substrate in the form of atoms or molecules, enhancing the adhesion to overcome stripping defects.Meanwhile, research has demonstrated that electrospun nanofibrous separators with high porosity and polar groups were easily modified to improve the electrolyte affinity and suppress the shuttle effect of LiPSs. [28,29] Polyacrylonitrile (PAN) Exploring a scalable strategy to fabricate a multifunctional separator is of great significance to overcome the challenges of lithium polysulfides (LiPSs) and dendritic growth in lithium-sulfur batteries (LSBs). Herein, a binder-free Janus separator is constructed by interfacial engineering. At the cathode interface, an ultra-thin covalent triazine piperazine film containing tailorable micropores and adsorption sites is decorated on polyacrylonitrile (PAN) membrane by in situ interfacial polymerization, building a triple barrier for LiPSs. The combination of steric hindrance and chemical adsorption reduces LiPS's migration by 81.85%. Me...

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Lithium-ion secondary batteries (LIB) have been deemed less favorable devices for portable electronic devices and electric vehicles due to their safety issues, high cost, and low theoretical energy density. [1][2][3] Compared to LIB, Li-S battery has superior theoretical specific capacity of 1675 mAh g −1 and good theoretical energy density of 2600 Wh kg −1 . [4,5] Li-S battery is thus considered one of the most promising candidates for next-generation highenergy density batteries. [6,7] However, the intrinsic limitations of Li-S batteries severely impede their commercial development. [7,8] Firstly, the inherent insulating nature of sulfur and insoluble Li 2 S leads to poor electrochemical kinetics, low utilization of active sulfur, and inferior coulomb efficiency. [9][10][11] Secondly, the soluble long-chain polysulfides may be dissolved in organic electrolyte, resulting in severe "shuttle effect" to cause rapid capacity decay and poor cycling performance. [12][13][14] Finally, the notorious "shuttle effect" could corrode lithium anode, exacerbating the growth and uneven deposition of lithium dendrites, severely affecting the rate performance and safety in use of Li-S battery. [15,16] Massive efforts have been taken to overcome these drawbacks of Li-S batteries. [17,18] For example, the insulating nature of sulfur can be addressed by hosting the sulfur in highly conductive graphene and carbon nanotubes frameworks. [19,20] Within the Li-S battery configuration, separator is used to prevent the direct contact between the cathode and anode, and dominates the key battery performances such as internal resistance, capacity, cycle property, and safety. [21] At present, commercial polyolefin (polypropylene and polyethylene) separators are generally used in Li-S batteries. However, these separators would bring about serious polysulfides "shuttle effect" due to the low porosity, poor electrolyte affinity, and inferior thermal stability, causing active sulfur substance loss, rapid capacity decay, and other issues. [22,23] Due to the high porosity, large specific surface area, and chemical stability, electrospun nanofiber membranes have been proved to be more effective as separators for Li-S batteries. [23,24] In addition, the strong affinity between the electrospun nanofiber membrane and electrolyte can significantly enhance the lithium-ion migration. [25,26] Electrospun cellulose acetate membrane has been used as separator in LIB due to its polar nature and strong affinity to electrolyte. [27] Electrospun nanofiber membranes containing oxygen-rich polar groups have been employed as Li-S battery separators to effectively inhibit "shuttle effect," owing to the strong binding energy between the oxygen and polysulfides. [28,29] Other than chemical adsorption of