Controlled selenization within a N-doped carbon shell enables stable MnO–MnSe heterointerfaces for long-life Li–S batteries

Abstract

In this study, a MnO–MnSe heterostructure encapsulated in a nitrogen doped carbon (NC) layer (MnO–MnSe@NC_(1:2.5)) was fabricated via controlled selenization and employed as a multifunctional coating for lithium–sulfur battery (LSB) separators. Research has revealed that the NC layer is crucial for enabling the selenization reaction, serving both as a confined space for the reaction and as a structural barrier preventing phase-induced collapse. The selenization ratio critically determines the material's structure: at 1 : 2.5, the composite retains NC integrity and high surface area while forming a well-defined heterointerface, whereas a higher ratio (1 : 5) weakens the heterostructure and degrades the NC, impairing overall performance. Benefiting from the high adsorption and catalytic activity of the MnO–MnSe heterojunction, the excellent pore structure and high conductivity of the NC layer, the moderately selenized MnO–MnSe@NC_(1:2.5) significantly enhances sulfur redox kinetics. The LSB based on the MnO–MnSe@NC_(1:2.5)//PP-modified separator exhibits outstanding rate performance (760.4 mAh g⁻¹ at 5C) and long-term cycling stability, retaining a capacity of 516.35 mAh g⁻¹ after 750 cycles at 1C with a cycle decay rate of merely 0.049%. This work identifies the NC layer and moderate selenization as key to building stable, highly active metal selenide heterojunctions, offering crucial guidance for future material design.