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 batteries (LSBs) separators. Research has revealed that the NC layer is crucial for enabling the selenide 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 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 LSBs based on 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 selenisation as key to building stable, highly active metal selenide heterojunctions, offering crucial guidance for future material design.