Ever increasing demand for efficient portable energy storage systems has directed researchers towards finding alternatives for the conventional insertion – based lithium-ion battery cathodes. Sulfur, with a theoretical specific capacity of 1672 mAh/g is a promising candidate for high energy density lithium battery cathodes1, 2. Low cost and ease of availability further adds to the advantages of sulfur over hitherto transition metal – based cathodes.
However, elemental sulfur has very low electronic conductivity (~10-15 S/cm)3 at room temperature which restricts the active material utilization in Li – S battery. The formation of soluble non – intercalation based polysulfide intermediates (Li2Sn; n = 2 – 8)4 during electrochemical cycling further results in active material loss by coating onto the anode leading to eventual battery failure.
Embedding sulfur into porous materials have shown considerable reduction in polysulfide dissolution by preventing direct contact with the liquid electrolyte5-7. However, inability to precisely control porosity and lack of chemical interaction between these porous structures and the entrapped sulfur greatly limits the efficiency of this approach. To completely prevent polysulfide dissolution, sulfur hosts with tunable, engineered porosity and increased affinity for polysulfide needs to be engineered.
In this work, chemically coupled conductive complex framework materials (C4FMs) with nanoporous structure were used as hosts for sulfur in Li – S battery. Introduction of special functional groups improves the affinity of these structures towards polysulfide. The frameworks were synthesized using microwave assisted hydrothermal synthesis and then infiltrated with sulfur using vapor infiltration techniques. These sulfur – hosted cathodes showed a stable electrochemical performance with an initial discharge capacity of ~1620 mAh/g which stabilized at 1100 mAh/g to100 cycles (Figure 1).
Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0006825, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM).
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