Solvent-engineered ZIF-67-derived cobalt-embedded carbon as polysulfide trapping host for high-stability Li–S battery

A metal organic framework (MOF)–derived cobalt-embedded nitrogen-doped carbon/sulfur composites (Co-NCS) from ZIF-67 template was generated and tested for lithium-sulfur (Li–S) battery. Solvent-engineered tunable morphology of ZIF-67 and its influences on lithium storage in Li–S battery were examined. A coin-type cell was employed for Li–S system having different Co-NCS composites cathode and lithium metal anode and its electrochemical performances were compared. The dodecahedron-shaped Co-NCS composite synthesized using water solvent (Co-NCS-W) showed superior performance with discharge capacity of 1000 mAh g⁻¹ at 0.02C-rate. This battery showed excellent cycle-life stability for about 500 charge/discharge cycles sustaining a 480 mAh g⁻¹ steady capacity at high C-rate of 0.1C. The superior performance was attributed to structural stability obtained through MOF synthesis route and presence of carbon matrix that served as a conducting network for charge transport as well as providing adequate room for sulfur cathode. The Co-NCS-W composite with Co–N sites leads to improved polysulfide trapping, resulting in excellent cycling stability. A significant amount of capacitive storage along with diffusive Li⁺ storage in all cathode hosts generated resulted in high-rate capability. The cathode demonstrated good capacity and superior rate capability, along with excellent cycle-life stability, making it ideal for high-performing Li–S batteries.

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