Fundamental role of Fe–N–C active sites in a CO2-derived ultra-porous carbon electrode for inhibiting shuttle phenomena in Li–S batteries

Abstract

The homogeneous distribution of electrochemical catalysts in a carbon material with an ultrahigh pore volume and large surface area is a promising strategy for rapid conversion of lithium polysulfides to minimize the shuttle phenomenon. This work utilizes a porous carbon material produced via facile CO₂ conversion to achieve both the confinement of sulfur and the uniform distribution of Fe–N–C sites. It also seeks to dope more N atoms and increase porosity through a unique method of bubbling an ammonia solution, which increases the density of the Fe–N–C catalytically active sites and forms additional pores, providing numerous pathways for more efficient diffusion of Li ions. The increased pore volume maximizes the kinetics of polysulfide conversion through synergy with the catalysts distributed over the high surface area of the resulting product. DFT calculations elucidate the fundamental role of the Fe–N–C catalyst in terms of the energy reduction associated with the lithium polysulfide conversion process and enhanced Li-ion diffusion dynamics. The assembled cell exhibits a capacity of 590 mA h g⁻¹ up to 150 cycles at a high current density of 7.0C, and a maximum areal capacity of 3.54 mA h cm⁻² is delivered at 1.0C for a high sulfur amount of 4.3 mg cm⁻².