# A Review of Lithium-Sulfur Batteries Based on Metal-Organic Frameworks: Progress and Prospects
## 2 Metal-Organic Frameworks for Cathode Applications in Lithium-Sulfur Batteries
### Original Metal-Organic Frame  
Original MOFs with regularly arranged crystalline structures of inorganic metal and organic components show great potential for storing reactive sulfur in a chain structure prior to discharge, as well as efficiently trapping PSs through chemical affinity and adapting to volume changes during discharge. The scientific development of MOFs as sulfur hosts in LSBs dates to 2011. [PERSON] et al. [43] reported a mesoporous chromium-based MOF, named MIL-100 (Cr) (MIL stands for Material Institut Lavoisier), as a host material for sulfur impregnation. Although 48 wt.% sulfur was successfully loaded into the pores of MIL-100 (Cr), which boasts a specific surface area of 1485 m\({}^{2}\) g\({}^{-1}\), the cycling stability of the battery was found to be poor. This was attributed to weak bonding between the polysulfides and the host material, resulting in inefficiencies during the battery's charge-discharge cycles. Subsequent studies of MOFs primarily concentrated on exploring the impact of MOF pore structure and pore size on their properties. For instance, [PERSON] and co-workers [PERSON] et al. [44] synthesized three flower-like microporous nitrogen-doped carbon nanosheets, designated as FMNCN-n (where \(n\) = 700, 800, and 900, corresponding to the controlled temperature used during synthesis), through the Zn-TDPAT carbonation of metal-organic frameworks (MOFs). As depicted in Figure 4a, these nanosheets exhibited distinct characteristics. The results indicated that FMNCN-900, obtained by carbonizing Zn-TDPAT at 900 \({}^{\circ}\)C, possessed an optimal pore volume and nitrogen content. Additionally, Figure 4b revealed a similar pore size distribution across all FMNCN-n compounds. The main pore size of FMNCN-900 is approximately 0.55 nm, which falls within the range of <0.6 nm. Notably, the pore size distribution of FMNCN-900 is predominantly centered around 0.55 nm. Among the three FMNCN-n materials, FMNCN-900 exhibits the highest pore volume for pore sizes below 0.6 nm, making it particularly suitable for accommodating small sulfur molecules. The prepared S@FMNCN-900 cathode material demonstrated exceptional electrochemical performance in lithium-sulfur batteries (LSBs) with carbonate as the electrolyte, as illustrated in Figure 4c. After 200 cycles at a rate of 0.1 C, the reversible capacity was approximately 1220 mAh g\({}^{-1}\). Furthermore, even after 1000 cycles at a higher rate of 2 C over an extended period, the reversible capacity remained around 727 mAh g\({}^{-1}\), with a minimal capacity loss of only about 0.02% per cycle. MOFs have been employed as templates for the synthesis of porous carbon materials that are embedded with metal oxides or doped with impurity atoms. These materials offer significant advantages in terms of their catalytic performance and ability to adsorb polysulfides. [PERSON] et al. [45] developed a core-shell structural template by growing zeolite imidazolate framework-67 (ZIF-67) on ZnO nanorods, as depicted in Figure 5a. This template features a bimetallic Zn/Co-MOF shell surrounding the ZnO core. Upon further carbonization, a hollow carbon composite, designated as Co/Co\({}_{3}\)O\({}_{4}\)-NHC, was obtained. This composite exhibits controllable particle size, a large microporous and mesoporous space, and a strong chemical affinity, making it a promising candidate for applications in lithium-ion batteries. As illustrated in Figure 5b, the adsorption experiment revealed that Co/Co\({}_{3}\)O\({}_{4}\)-NHC exhibits a significantly higher adsorption capacity for lithium polysulfide than the other two materials. After 100 cycles, the battery was disassembled, and a comparison of the diaphraggrams further confirmed that Co/Co\({}_{3}\)O\({}_{4}\)-NHC possessed a markedly stronger adsorption capacity. As shown in Figure 5c, the S@Co/Co\({}_{3}\)O\({}_{4}\)-NHC cathode maintained its morphology well after cycling, indicating that the Co/Co\({}_{3}\)O\({}_{4}\)-NHC composite effectively inhibits the dissolution of lithium polysulfides (LiPSs).