Phosphorus doped hierarchical porous carbon nanosheet array as an electrocatalyst to enhance polysulfides anchoring and conversion

Abstract

The sluggish redox kinetics and severe lithium polysulfides (LiPSs) shutting effect in lithium sulfur batteries (LSBs) greatly hinder their practical applications. In this work, phosphorus doped carbon nanosheet array (MPC) separator coating layer was synthesized by MgO template, and used as metal-free electrocatalyst to concurrently fulfill efficient polysulfide interception and conversion. By regulating the addition of phytic acid, copolymerization rate of formaldehyde, resorcinol and phytic acid can be conveniently adjusted to form a hierarchical porous MPC microstructure. Phosphorus doping introduces surface defects and enhances the polarity of MPC, which exhibits a metal-like LiPSs anchoring effect by forming Li-P and S-P bonds, avoiding the undesirable oxidation of LiPSs during adsorption. Symmetrical cell and Li2S precipitation experiments reveal that phosphorus doping reduces energy barrier for LiPSs reactions and facilitates Li2S precipitation behavior, exhibiting a strong electrocatalytic effect on Li-S chemistry. Stemming from the above advantages of MPC coated separator, cells exhibit a low interfacial reaction resistance and good anode stability. A capacity of 1161 mAh g−1 at 0.2C and a low attenuation of 0.056% per cycle at 1C over 800 cycles are achieved. For a high sulfur loading up to 4 mg cm−2, the areal capacity can still be stabilized at 2.86 mAh cm−2.