# 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
### Metal-Organic Framework Composites
#### 2.2.2 Composites with Carbon Nanotubes (CNTs)  
In contrast to graphene, carbon nanotubes (CNTs) exhibit one-dimensional tubular structures, yet their structural versatility enables researchers to customize them according to specific requirements [50; 51]. [PERSON] et al. [52] synthesized metal-organic framework-74-Ni/carbon nanotube (MOF-74-Ni/CNT) composites by an in situ hydrothermal reaction in a one-pot method form; see Figure 7a. This distinctive architecture not only offers a high density of open metal sites to anchor polysulfides but also ensures extended electricalcontacts. What is particularly novel is that [PERSON] et al. [53] exploited the different thermal stabilities between ZIF-67 and ZIF-8 to synthesize carbon nanotubes (CNTs) grafted onto nitrogen-doped carbon@graphitic carbon nanocages (CNT-NC@GC) through the pyrolysis of the core-shell structured ZIF-8@ZIF-67. The design incorporates several structural merits. The carbon shell, characterized by high porosity and a high specific surface area, not only offers ample space for loading high quantities of sulfur but also significantly diminishes ion/electron transfer pathways. Consequently, the CNT-NC@GC/S composite, with a sulfur content nearing 80%, experiences enhanced utilization of the active material [54]. Figure 7b illustrates the formation process of the CNT-NC@GC/S cathode material. Additionally, Figure 7c presents the TEM image along with the corresponding elemental mapping of ZIF-8@ZIF-67, comprising a ZIF-8 core encapsulated within a ZIF-67 shell. Based on the most recent experiments, [PERSON] et al. [55] synthesized the reactive material CoMoS\({}_{3.13}\)@NCNTs by initially coating an MOF material onto metal oxides as a precursor. This precursor was subsequently treated with sulfide to ultimately yield a composite rod-layer structure of the active material, as depicted in Figure 7d. During the synthesis process, the MoO\({}_{3}\)@ZIF-67 precursor formed nanorod-like structures with numerous voids through ion exchange with S\({}^{2-}\) ions and mutual ion exchange between Mo ions in MoO\({}_{3}\) nanorods and Co ions in ZIF-67. Figure 7e demonstrates that after 400 cycles, the CoMoS\({}_{3.13}\)@NCNTs maintain a discharge capacity of 785 mAh g\({}^{-1}\) with a Coulombic efficiency of 97%. In comparison, they exhibit an advantage over CoMoS\({}_{3.13}\). Hence, due to their excellent electrical conductivity and high specific surface area, CNTs have been widely employed to boost the rate capability and elevate the sulfur content in MOF-based composite materials.  
Figure 6: (**a**) Graphical representation of the sulfur loading procedure in a representative MOF-808 (top panel) and cartoon representations of different electrode compositions highlighting the bulk densities provided by the various components (bottom panel) (reprinted/adapted with permission from [48]; copyright 2020, _Applied Materials_). (**b**) Schematic representation of the synthesis of In-IPA@FOO/S composites. (**c**) SEM image of In-IPA@rGO. (**d**) EDS mapping of In-IPA@rGO/S (reprinted/adapted with permission from [49]; copyright 2022, _Ceramics International_).