Se-Regulated MnS Porous Nanocubes Encapsulated in Carbon Nanofibers as High-Performance Anode for Sodium-Ion Batteries

Abstract

Manganese-based chalcogenides have significant potential as anodes for sodium-ion batteries (SIBs) due to their high theoretical specific capacity, abundant natural reserves, and environmental friendliness. However, their application is hindered by poor cycling stability, resulting from severe volume changes during cycling and slow reaction kinetics due to their complex crystal structure. Here, an efficient and straightforward strategy was employed to in-situ encapsulate single-phase porous nanocubic MnS0.5Se0.5 into carbon nanofibers using electrospinning and the hard template method, thus forming a necklace-like porous MnS0.5Se0.5-carbon nanofiber composite (MnS0.5Se0.5@N-CNF). The introduction of Se significantly impacts both the composition and microstructure of MnS0.5Se0.5, including lattice distortion that generates additional defects, optimization of chemical bonds, and a nano-spatially confined design. In situ/ex-situ characterization and density functional theory calculations verified that this MnS0.5Se0.5@N-CNF alleviates the volume expansion and facilitates the transfer of Na+/electron. As expected, MnS0.5Se0.5@N-CNF anode demonstrates excellent sodium storage performance, characterized by high initial Coulombic efficiency (90.8%), high-rate capability (370.5 mAh g−1 at 10 A g−1) and long durability (over 5000 cycles at 5 A g−1). The MnS0.5Se0.5@N-CNF //NVP@C full cell, assembled with MnS0.5Se0.5@N-CNF as anode and Na3V2(PO4)3@C as cathode, exhibits a high energy density of 254 Wh kg−1 can be provided. This work presents a novel strategy to optimize the design of anode materials through structural engineering and Se substitution, while also elucidating the underlying reaction mechanisms.

1. Introduction

With the ever-increasing demand for electrically powered transportation vehicles, portable electronic devices, and renewable energy storage systems in modern society, the limited availability of lithium resources has posed significant challenges to the sustainable development of lithium-ion batteries (LIBs) for large-scale applications [1]. In contrast, sodium-ion batteries (SIBs) have emerged as a promising alternative to LIBs, due to the abundance of sodium (2.27% vs. lithium 0.002% of the Earth’s crust), low cost, and relatively high environmental friendliness [2]. However, the larger ionic radius of Na+ (0.102 nm vs. Li+ 0.076 nm) and its greater atomic mass (22.99 g mol−1 vs. Li+ 6.94 g mol−1) make it more difficult for sodium-ions to intercalate and de-intercalate in anode materials, which results in SIBs still facing challenges in energy density, power performance, and cycle life [3–5]. Therefore, continuous technological innovation and material optimization are expected to further enhance the sodium storage performance of SIB anode materials.

Transition metal chalcogenides (TMSs) are considered promising anode materials for SIBs due to their high theoretical capacity and good electrochemical activity [6]. Among them, manganese sulfide (MnS) has attracted significant attention due to its advantages, such as abundant reserves, low cost, and a high theoretical capacity of up to 616 mAh g−1 [7]. However, the critical problems of the large volume changes, inherently mediocre conductivity, slow Na+ reaction kinetics and high solubility of polysulfides during the continuous sodiation/desodiation process result in poor cyclability and inferior rate capability, which significantly hinders their practical applications [8–11]. In this regard, several strategies have been proposed to address these challenges: (i) the introduction of highly conductive carbon frameworks, which have proven effective in enhancing conductivity and providing structural support [12]. However, the poor interfacial binding between polar TMSs and carbon often leads to weak adhesion and limited long-term stability.