Iron Sulfide Embedded Nanostructured Carbon Materials for High-Performance Lithium and Sodium-Ion Batteries

Abstract

The development of high energy density lithium and sodium ion batteries (LIBs) with stable cycle performance is of significant importance, recently, due to the emerging energy demands like energy storage systems and electric vehicles. The low theoretical capacities offered by commercialized intercalation based cathode materials (such as LiFePO4 and LiCoO2) limit the high energy density applications of the present era, substantially. However, the transition metal based conversion materials (MX, X=oxides, fluorides and sulfides, M= Fe, Co, Mn, Cu, Ni) can store more than one Li or Na ion per transition metal leading to high theoretical capacities with moderate operating potentials. Iron sulfide (FeS) is an inexpensive and environmentally benign material, with a high theoretical capacity of 609 mAh/g. Nevertheless, the FeS based electrodes suffer from limited cycle life because of the large volume changes (up to 200 %) encountered upon cycling, which eventually destroys the electrode structure. The generation of polysulfide intermediates during the cycling process further accelerates the capacity decay. The present work investigates in detail, the lithium or sodium ion storage in iron sulfide embedded nanostructured carbon materials synthesized. The presence of nano-sized FeS particles in the composites improves the sluggish reaction kinetics whereas the one-dimensional morphology of the conductive carbon matrix encapsulating them shortens the lithium or sodium-ion diffusion pathway and promotes rapid electron transfer. The carbon matrix encapsulating the FeS nanoparticles can effectively accommodate the volume changes and associated strains encountered during the cycling process. The electrochemical performances of the synthesized FeS nanoparticle loaded nanostructured carbon composite confirm the superior reversibility of the electrode with superior cycling stability and specific capacity.