Pyridyl Porphyrin as Electrocatalyst: Regulating the Redox Conversion of Lithium Polysulfides under Voltage

The binding correlation between electrocatalyst and lithium polysulfides (LiPSs) determines the regulation of LiPSs' redox conversion. However, how the correlation works on the LiPSs under voltage remains obscured. In this paper, the pi-conjugated aromatic pyridyl porphyrin with nitrogen of a lone pair of electrons is introduced as electrocatalyst to accelerate redox kinetics and inhibit polysulfides shuttle. On the foundation of DFT calculation and experimental tests, it is stated that the chemical binding between pyridyl porphyrin and lithium polysulfides is beefed up under higher voltage, which facilitates the charge transfer. Moreover, the molecular dynamics (MD) simulation of the solid-liquid model shows that the presence of pyridyl porphyrin increases the binding chances between Li+ and S62- and forms clusters rather than dissolving in electrolyte, which is good for charge transfer and polysulfides localization. By hybridizing the pyridyl porphyrin with conductive cathode matrix of carbon nanotube and graphene oxide, the as-fabricated Li2S-T4PP-GO-CNT cathode delivers a high initial discharge capacity of 996.4 mAh g-1 at 0.1 C. The as-made batteries with good electrochemical performance therefore show potential for trouble-shooting and commercial utilization of lithium-sulfur batteries (LSBs) in the future. The chemical binding between pyridyl porphyrin and lithium polysulfides is beefed up under higher voltage, which facilitates the charge transfer. Besides, the presence of pyridyl porphyrin increases the binding chances between Li+ and polysulfides and forms clusters rather than dissolving in electrolyte, which is good for charge transfer and polysulfides localization/conversion.image