Constructing Atomic Fe and N Co-doped Hollow Carbon Nanospheres with a Polymer Encapsulation Strategy for High-Performance Lithium-Sulfur Batteries with Accelerated Polysulfide Conversion.

Abstract

As competitive next-generation rechargeable batteries, lithium-sulfur batteries (LSBs) suffer from the shuttle effect and the sluggish kinetics of intermediate polysulfides during charge and discharge processes, adversely affecting their electrochemical performances and actual applications. Herein, we demonstrate a polymer encapsulation strategy to synthesize atomic Fe and N co-doped hollow carbon nanospheres (Fe-NHC) with Fe-Nx sites for modifying commercial PP separator of LSBs to suppress the shuttle effect and promote the kinetics of intermediate polysulfides. Benefiting from the excellent structural design, the doped-N with positive charges could effectively adsorb negatively charged soluble polysulfides, help attract the soluble polysulfides to the Fe atoms and boost the catalytic transformation of the soluble polysulfides. Additionally, such a thin carbon shell could provide a short mass diffusion pathway and hence promote the adsorption and the catalytic conversion. Therefore, the battery with the Fe-NHC/PP separator delivers outstanding cycling and rate performances. At the large current density of 1 C, the specific capacity is 1079 mA h g-1 and maintains a low loss of 0.076 % per cycle within 500 cycles. Even at a harsh current density of 4 C, a high capacity of 824 mA h g-1 is still achieved, indicating the advantage of the Fe-NHC/PP separator in LSBs.