Interface engineering of Fe3Se4/FeSe heterostructures encapsulated in MXene for boosting LiPS conversion and inhibiting shuttle effect

Developing advanced catalysts with high chemisorption toward promoting the conversion of lithium polysulfide (LiPS) is the key to the commercial application of Lithium-sulfur (Li-S) batteries. Here, a novel catalyst consisting of Fe3Se4/FeSe heterojunctions encapsulated in two-dimensional (2D) MXene nanosheets is prepared by in situ growth and selenization of Fe-MOFs. The MXene skeleton captures polysulfides effectively and the Fe3Se4/FeSe heterojunction plays a catalytic role as well as their strong synergistic effect achieves capture-adsorption -catalysis of LiPS. A Li-S battery with Fe3Se4/FeSe@MXene-PP separator delivers a high specific capacity (1104.2 mAh/g at 0.2C) and outstanding rate capacity (758.8 mA h g-1 at 4C). Even with sulfur loading as high as 5.8 mg cm-2, the Li-S battery has a high specific capacity of 862.6 mAh/g at 0.2C and cycle stability (92.3 % retention after 120 cycles). The involved mechanisms of performance improvement were discussed and demonstrated by density function theory (DFT) calculations and in situ Raman analysis. Interface engineering of the Fe3Se4/FeSe increases the density of states at the Fermi level, reduces the activation energy of Li2S decomposition, and the establishment of an internal electric field accelerates charge transfer. This work provides an effective approach to the design of high-performance catalysts for improved Li-S batteries.

Automated summary

In this study, a novel catalyst composed of Fe3Se4/FeSe heterojunctions encapsulated in two-dimensional MXene nanosheets was prepared. The catalyst exhibited efficient capture, adsorption, and catalytic conversion of lithium polysulfide in Lithium-sulfur batteries. The Li-S battery with the Fe3Se4/FeSe@MXene-PP separator showed high specific capacity and outstanding rate capacity, as well as good cycle stability even with high sulfur loading.