# A Review of Lithium-Sulfur Batteries Based on Metal-Organic Frameworks: Progress and Prospects
## 3 Alternative Strategies for Metal-Organic Frameworks to Improve the Performance of LSBs
### Separators Modified by Metal-Organic Framework Materials  
The dissolution of polysulfides and resulting shuttle effects are the primary obstacles hindering the long-term cycle life and capacity retention of LSBs. To address these challenges, [PERSON] et al. (2018) used a one-step solid solution phase synthesis method to design efficient separators that were modified with bifunctional bimetallic MOFs (Figure 11a). Figure 11b clearly shows by CV redox peaks that the cathodic peak intensity of Fe-ZIF-8/PP increases and anodic peak decreases as compared to ZIF-8/PP and PP, which suggests the effective conversion of polysulfides by Fe-ZIF-8/PP. LSBs with PP and ZIF-8/PP, Fe-ZIF-8/PP separators, S-CNT/GO anodes, and Li-negative electrodes were assembled into 2032-type coin cells and their long-term cycling performance was evaluated. As shown in Figure 11c, the discharge capacity of Fe-ZIF-8/PP is 865 mAh g\({}^{-1}\), and the capacity after 1000 cycles is 409 mAh g\({}^{-1}\), with a Coulombic efficiency of \(\approx\)100% at 0.5 C. The layers modified using current techniques exhibit gaps between the MOFs that are considerably larger than the MOFs' inherent pore size. Polysulfides and lithium ions inevitably pass through these gaps, hindering the full utilization of the structural benefits. [PERSON] and [PERSON] et al. (2018) formed ultra-thin (20 nm) and crack-free MOF films on the diaphragm by atomic layer deposition (ALD) (Figure 11d). The confinement of polysulfides by ZIF-8 films was observed by the simplest visual experiment, as shown in Figure 11e for the permeation test of a double L device separated by F/ZIF-PP, G-PP diaphragm. The device with G-PP separator showed no significant penetration of polysulfides at the beginning due to the physical blockage of the ZIF particle layer. After 12 h, the electrolyte on the right side of the device began to turn yellow and progressively darkened, indicating that the polysulfide shuttle effect was gradually intensifying. For the unit with the F/ZIF-PP separator, there was almost no penetration of polysulfides even after 48 h, and by comparing the F/ZIF-PP showed good performance. Functional coatings on separators not only play a crucial role in regulating pore size, interfacial properties, wettability, porosity and the internal structure of the membrane but they are also a key factor in the development of the membrane ([PERSON] et al., 2018; [PERSON] et al., 2018). It also enhances the membrane's ion transport capability and regulates lithium polysulfide intermediates via both physical and chemical constraints, providing sufficient active sites for the anchoring and conversion of lithium polysulfide intermediates ([PERSON] et al., 2018; [PERSON] et al., 2018; [PERSON] et al., 2018; [PERSON] et al., 2018). [PERSON] et al. (2018) prepared a new separator based on a coating design, where Zn-MOF was synthesized and then Y-MOF was grown on its surface. Subsequently, Y\({}_{2}\)O\({}_{3}\)/ZnO@C composites were synthesized by high-temperature calcination, which were finally coated on polyethylene separators. Figure 11f displays a TEM image of ZnO@C, revealing its distinctive rod-like structure. Upon revisiting Figure 11g, we observe a TEM image of Y\({}_{2}\)O\({}_{3}\)/ZnO@C, where smaller Y\({}_{2}\)O\({}_{3}\)@C particles are visibly growing on the surface of the ZnO@C rods. To evaluate the electrochemical performance of the modified separators, Y\({}_{2}\)O\({}_{3}\)/ZnO@C, ZnO@C, and Y\({}_{2}\)O\({}_{3}\)@C were used on one side of the separator, followed by the assembly of the cells and long-term cycling tests. Figure 11h presents the charge-discharge profiles of various separators at a rate of 0.5 C. It is evident that Y\({}_{2}\)O\({}_{3}\)/ZnO@C shows a stable plateau and achieves the highest specific charge-discharge capacity.