Li-S chemistry is regarded as a very promising next-generation battery technology. Its complex redox process and particularly long-chain lithium polysulfides (LPS) shuttling, however, are hindering the development of a practical Li-S battery technology. Catalysts are being investigated to promote this complicated redox cycle in addressing LPS shuttling problem and expediting reaction kinetics. Here we report single metal atom catalysts used in Li-S batteries. Single atom catalysts (SACs) are synthesized using a modified metal organic framework (MOF)-based approach, in which the low vapor pressure metal elements substitute Zn during pyrolysis of ZIF-8 to attain M-N₄ moieties by being coordinated with 4 substitutional N atoms in the graphene lattice. A freestanding 3D structure with SAC-functionalized carbon nanocages linked by carbon nanofibers is applied as the sulfur cathode scaffold. Here the nanocages are derived from metal species doped ZIF with MN_x SAC moieties embedded on the inside and outside surfaces, and the CNFs are derived from electrospun polyacrylonitrile nanofibers. We report different methods in assessing SAC function on sulfide redox reactions for the prepared electrode in cells with different LiSx electrolytes. Electrochemical studies, particularly charge-transfer kinetics during the discharge and charge processes and charge transfer resistance will be presented.