Defect Induced Performance Enhancement of Monolayer MoS₂ for Li- and Na-Ion Batteries

Dexterity in the application of defect engineering implicates modification in the physical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) to enhance their effectiveness toward nanoelectronics applications. Subsequently, the existence of various types of defects in monolayer MoS₂ has been employed to inculcate and implement their significance in enhancing the Li/Na-ion storage capability of MoS₂ monolayers as anodes of lithium ion batteries (LIBs) and sodium ion batteries (SIBs). DFT calculations have guided us to traverse the effect of various point and antisite defects on Li/Na adsorption energy and the diffusion barrier of monolayer MoS₂. Before looking into Li/Na adsorption properties of defective MoS₂, the structural stability of various defects is explored with relevance to their formation energy. This also germinates the quest for the most stable defective structures that could be a reliable anode material for LIBs and SIBs. Enhanced adsorption is found for both Li/Na ions in the case of defective MoS₂ over that corresponding to pristine MoS₂. To study the level of interaction between Li/Na and defective MoS₂, electronic structure analysis has been performed. To evaluate the possible migration pathways and rate of migration of Li/Na over defective MoS₂, we calculated the diffusion barrier energy through the CI-NEB method. Our study demonstrates that the formation of vacancy improves the diffusion performance of both lithium and sodium at the defective region which are prerequisites for LIBs and SIBs. Additionally, we demonstrated that the formation of vacancy could improve the specific capacity of monolayer MoS₂ due to a decrease of the molecular mass of defective MoS₂ in comparison to pristine MoS₂. However, the OCV is not affected much due to enhanced adsorption. Hence, designing MoS₂ nanostructures with defects is a useful strategy to achieve an effective anode material for obtaining high capacity LIBs and SIBs by precisely tailoring its properties for desired applications, such as enhancing the adsorption energy, modulating the reaction pathway, and raising the specific capacity.