Two-Dimensional Group IV Monochalcogenides: Anode Materials for Li-Ion Batteries

Abstract

The selection of a suitable electrode material is a fundamental step in the development of Li-ion batteries (LIBs) to achieve enhanced performance. In the present study, we have explored the feasibility of monolayers of phosphorene analogues, namely, group IV monochalcogenides (SiS, SiSe, GeS, GeSe, SnS, and SnSe), to serve as anode materials in LIBs by density functional theory (DFT). Our exploratory study indicates that lithium binds efficiently to these monolayers, with Li@SiS and Li@SiSe showing appreciable stability comparable to that of phosphorene. The zero-point-energy-corrected minimum-energy pathway (MEP) for Li diffusion demonstrates high anisotropy for both SiS and SiSe, with a low diffusion barrier of ∼0.15 eV along the zigzag direction. Inclusion of corrections due to quantum effects such as the zero-point energy (ZPE) and quantum mechanical tunneling (QMT) increases the diffusion rates by 6–10% at room temperature and results in increasingly significant contributions as the temperature is reduced (40–55% increment at T = 100 K). The calculated theoretical capacities for SiS and SiSe are 445.7 and 250.44 mA h g–1, respectively, which are well above those of existing commercially available anode materials. Both SiS and SiSe preserve their structural integrity upon lithiation, justifying their role as host materials for lithium. A semiconductor → metallic transition is observed upon full lithiation for both materials. All of these exceptional properties, including low diffusion barrier, moderate to high specific capacity, low open-circuit voltage (OCV), small volume change, and good electrical conductivity, suggest that monolayer SiS and SiSe could serve as promising electrode materials in LIBs.