Regulating the polysulfide redox conversion by iron phosphide nanocrystals for high-rate and ultrastable lithium-sulfur battery

Abstract

Lithium sulfur (Li-S) batteries have attracted considerable attention as the next generation rechargeable batteries owing to their much higher energy density in contrast to the conventional lithium ion batteries (LIBs). However, the inferior cycling performance as well as rate capability, resulted from the polysulfides shuttle effect and sluggish reaction kinetics, remains as major hurdles for its practical application. Herein, a high-rate and ultrastable Li-S battery has been demonstrated by using the multifunctional iron phosphide (FeP) nanocrystals as an efficient host material to anchor the polysulfides and regulate the polysulfide redox conversion. Density functional theory (DFT) calculations indicate that FeP can provide strong chemical bonding towards polysulfides. The FeP nanocrystals show high catalytic effect to facilitate the polysulfides conversion reaction and lower the Li2S nucleation energy. Additionally, the 3D rGO-CNTs scaffold enables fast and continuous long-distance electron transportation and accommodates large volumetric change during the charge/discharge processes. As a result, the FeP nanocrystals with intrinsic polysulfide affinity and catalytic activity suppress the polysulfide dissolution and enhance the redox reaction kinetics, enabling ultrastable cycling (0.04% capacity decay per cycle) and excellent rate performance (613.1 mAh g−1 at 3 C). Significantly, the enhanced Li-S performances provide significant insight for realizing high performance Li-S batteries by incorporating the metal phosphides into the sulfur cathode.