WN0.67-Embedded N-doped Graphene-Nanosheet interlayer as Efficient Polysulfide Catalyst and Absorbant for High-Performance Lithium-Sulfur Batteries

Abstract Lithium-sulfur (Li-S) battery has attracted wide research attention due to its high energy density, high earth-abundance and low-cost. However, the dissolution of lithium polysulfides (LiPSs) and corresponding shuttle will lead to serious capacity degradation and worse cycling stability of Li-S batteries. To address such issues, herein, we firstly present a novel interlayer of WN0.67-embedded N-doped graphene-nanosheets (WN0.67@NG) via a facile solvothermal reaction followed by nitriding treatment. The Li-S cell equipped with WN0.67@NG modified polypropylene (PP) separator exhibits outstanding electrochemical performances: a long-term stability with only a capacity decay of 0.07% per cycle over 200 cycles and a large capacity of 725 mAh g-1 at 4 C; interestingly, a favorable capacity of 776 mAh g-1 can be maintained after 100 cycles at 0.2 C for assembled Li-S pouch cell under a high sulfur loading conditions of 4.3 mg cm-2 with lean electrolyte occupation (6 μL mg-1). The outstanding performance can be attributed to the following advantages of WN0.67@NG interlayer: the high conductivity of NG sheets can facilitate the electron transfer and act as a physical block for restricting the LiPSs shuttle; most importantly, the polar WN0.67 nanoneedles embedded on the NG sheets not only provide abundant active sites for chemisorption and catalytic conversion of LiPSs, but also contribute to the nucleation and growth of Li2S; further theoretical calculations and in-situ Raman spectra clearly reveal the adsorption and catalytic conversion mechanism of WN0.67@NG interlayer at the molecular level. The work provides new insight into rational design and facile fabrication of multifunctional separators for industrial applications in high-performance Li-S batteries.