Adsorption and Diffusion of Lithium and Sodium on Defective Rhenium Disulfide: A First Principles Study

Single-layer rhenium disulfide (ReS₂) is a unique material with distinctive, anisotropic electronic, mechanical, and optical properties and has the potential to be used as an anode in alkali-metal-ion batteries. In this work, first principles calculations were performed to systematically evaluate the potential of monolayer pristine and defective ReS₂ as anodes in lithium (Li)- and sodium (Na)-ion batteries. Our calculations suggest that there are several potential adsorption sites for Li and Na on pristine ReS₂, owing to its low-symmetry structure. Additionally, the adsorption of Li and Na over pristine ReS₂ is very strong with adsorption energies of -2.28 and -1.71 eV, respectively. Interestingly, the presence of point defects causes significantly stronger binding of the alkali-metal atoms with adsorption energies in the range -2.98 to -3.17 eV for Li and -2.66 to -2.92 eV for Na. Re single vacancy was found to be the strongest binding defect for Li adsorption, whereas S single vacancy was found to be the strongest for Na. The diffusion of these two alkali atoms over pristine ReS₂ is anisotropic, with an energy barrier of 0.33 eV for Li and 0.16 eV for Na. The energy barriers associated with escaping a double vacancy and single vacancy for Li atoms are significantly large at 0.60 eV for the double-vacancy case and 0.51 eV for the single-vacancy case. Similarly, for Na, they are 0.59 and 0.47 eV, respectively, which indicates slower migration and sluggish charging/discharging. However, the diffusion energy barrier over a Re single vacancy is found to be merely 0.42 eV for a Li atom and 0.28 eV for Na. Overall, S single and double vacancies can reduce the diffusion rate by 10³-10⁵ times for Li and Na ions, respectively. These results suggest that monolayer ReS₂ with a Re single vacancy adsorbs Li and Na stronger than pristine ReS₂, with negligible negotiation with the charging/discharging rate of the battery, and therefore they can be used as an anode in Li- and Na-ion batteries.