A systematic correlation between morphology of porous carbon cathode and electrolyte in lithium-sulfur battery

Porous carbon has been applied for lithium-sulfur battery cathodes, and carbonized metal–organic framework (MOF) is advantageous in tuning the morphology. Herein, we have systematically synthesized water-distorted MOF (WDM) derived porous carbon via controlling the proportion of both water in a mixed solvent (dimethylformamide and water) and ligand in MOF-5 precursors (metal and ligand), which is categorized by its morphology (i.e. Cracked stone (closed), Tassel (open) and Intermediate (semi-open)). For example, decrease in water and increase in ligand content induce Cracked stone WDMs which showed the highest specific surface area (2742–2990 m²/g) and pore volume (2.81–3.28 cm³/g) after carbonization. Morphological effect of carbonized WDMs (CWDMs) on battery performance was examined by introducing electrolytes with different sulfur reduction mechanisms (i.e. DOL/DME and ACN₂LiTFSI-TTE): Closed framework effectively confines polysulfide, whereas open framework enhances electrolyte accessibility. The initial capacities of the batteries were in the following order: Cracked stone > Intermediate > Tassel for DOL/DME and Intermediate > Tassel > Cracked stone for ACN₂LiTFSI-TTE. To note, Intermediate CWDM exhibited the highest initial capacity and retained capacity after 100 cycles (1398 and 747 mAh/g) in ACN₂LiTFSI-TTE electrolyte having advantages from both open and closed frameworks. In sum, we could correlate cathode morphology (openness and pore structure) and electrolyte type (i.e. polysulfide solubility) with lithium-sulfur battery performance.