# 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
### Electrolytes Modified by Metal-Organic Framework Materials  
The degradation of lithium anodes in LSBs poses a significant threat to their safety and recyclability. The uneven distribution of lithium during repeated plating/stripping processes leads to the formation of 'dead lithium' and subsequent capacity loss. Furthermore, it destabilizes the solid electrolyte interphase (SEI) layer, as reported in studies ([PERSON] et al., 2018; [PERSON] et al., 2018). In conventional LSBs, the lithium anode operates in a highly complex environment, where insoluble Li\({}_{2}\)S and Li\({}_{2}\)S\({}_{2}\) accumulate on its surface due to the shuttle effect of solublepolysulfides. Therefore, the stabilization of lithium anodes is of great significance for the application of LSBs. Based on such problems, [PERSON] et al. [90] used a novel gel polymer electrolyte (GPE) with immobilized anions, which allowed the PVDF-based GPE to be modified and fabricated as a function of the distance between the two electrodes. The GPE was designed to be a 100 nm  
a semi-solid electrolyte by vacuum filtration method using Mg-MOF-74 material. From Figure 12a, it can be seen that the modified GPE can immobilize not only large-sized polysulfide anions but also TFSI-anions, thus promoting uniform lithium-ion flux and homogeneous lithium deposition. Figure 12b shows the ionic conductivity of the three electrolytes; the ionic conductivity of Celgard electrolyte stays at the lowest value of 3.43 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\), whereas the ionic conductivity of PVDF electrolyte and MOF-PVDF electrolyte are relatively large at 4.26 \(\times\) 10\({}^{-4}\) and 6.72 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\), respectively. While the resistance value of the MOF-modified PVDF electrolyte was marginally higher than that of the pristine PVDF electrolyte, the performance of MOF-modified GPE for LSBs could be seen to be improved due to the increase in thickness and the corresponding ionic conductivity after MOF modification. Different from the above, the all-solid-state electrolyte is compatible with higher specific capacity positive and negative electrode materials, and the solid-state electrolyte has a certain mechanical strength, which can better inhibit the growth of lithium dendrites and resist external stress impact. [PERSON] et al. [91] proposed a strategy to prepare MOF-related composite solid-state electrolytes (CSEs) for all-solid-state lithium-sulfur batteries (ASLSBs) using ordered MOFs as fillers. As a conceptual demonstration, MIL-125-NH2 (termed 3D MPPLCSE) was successfully prepared by electrospinningning and calendering methods with an ordered distribution in a PEO-based electrolyte. An increase in the presence of free TFSI ions on the electrolyte surface of 3D MPPL CSE compared to MPL CSE and PL CSE was shown by Raman results. This suggests that, due to the unique ordered-MOF structure, 3D MPPL CSE can effectively immobilize anions and dissociate LiTFSI through open Ti sites, thereby increasing lithium concentration and potentially enhancing the ionic conductivity of the electrolyte. The decomposition of PL CSE commenced at 350 \({}^{\circ}\)C, whereas both MPL CSE and 3D MPPL CSE exhibited lower decomposition temperatures, specifically, 336 \({}^{\circ}\)C and 327 \({}^{\circ}\)C, respectively. This suggests a greater abundance of amorphous PEO regions within the 3D MPPL CSE and MPL CSE compared to PL CSE. Furthermore, experimental observations revealed that under thermal shock conditions (200 \({}^{\circ}\)C for 0.5 h), both MPL CSEs and PL CSEs underwent melting. In contrast, the size and morphology of 3D MPPL CSEs remained largely unchanged. These findings indicate that the ordered arrangement of MIL-125-NH2 within the 3D MPPL CSE effectively inhibits the crystallization of PEO molecular chains. This structured alignment not only stabilizes the material against thermal stress but also facilitates lithium-ion conduction along the surface of the filler particles, ultimately enhancing the ionic conductivity of the composite.