Lithium-sulfur (Li-S) batteries are attracting attention as an energy storage system because they can provide higher theoretical capacity and energy density than lithium ion batteries. However, it is difficult to maintain a high capacity steadily due to the elution phenomenon of lithium polysulfide generated during the charging and discharging process, which is a primary obstacle to the commercialization of lithium sulfur batteries. In order to overcome this shuttle phenomena, the single atom catalyst has been applied to the Li-S battery system. The single catalyst has the advantage of maximizing the redox reaction performance even with its very small amount present in a high surface area support material. In this work, the role of single atom catalyst is analyzed thermodynamically through density functional theory (DFT) calculations and it will be supported by electrochemical measurements. To be specific, DFT calculations elucidate the fundamental role of the Fe-N-C catalytic sites (Fe-N2 and Fe-N4) in terms of the energy reduction associated with the lithium polysulfide conversion process, and enhanced Li-ion diffusion dynamics according to the nitrogen coordination number around the Fe single atom. As a result, the configuration of Fe-N2 and Fe-N4 could significantly reduce the energy required in the lithium sulfide redox reaction, which in-depth thermodynamically demonstrates the role of monoatomic catalysts.

Analysis of thermodynamic energy landscapes according to the coordination number of lithium polysulfide capturing sites in lithium-sulfur batteries

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