First-Principles Study of 3R-MoS₂ for High-Capacity and Stable Aluminum Ion Batteries Cathode Material

Currently, exploring high-capacity, stable cathode materials remains a major challenge for rechargeable Aluminum-ion batteries (AIBs). As an intercalator for rechargeable AIBs, Al³⁺ produces three times the capacity of AlCl₄^- when the same number of anions is inserted. However, the cathode material capable of producing Al³⁺ intercalation is not a graphite material with AlCl₄^- intercalation but a transition metal sulfide material with polar bonding. In this paper, the insertion mechanism of Al³⁺ in 3R-MoS₂ is investigated using first-principles calculations. It is found that Al³⁺ tends to insert into different interlayer positions at the same time rather than occupying one layer before inserting into another, which is different from the insertion mechanism of AlCl₄^- in graphite. Ab initio, molecular dynamics calculations revealed that Al³⁺ was able to stabilize the insertion of 3R-MoS₂. Diffusion barriers indicate that Al³⁺ preferentially migrates to nearby stabilization sites in diffusion pathway studies. According to the calculation, the theoretical maximum specific capacity of Al³⁺ intercalated 3R-MoS₂ reached 502.30 mAg h^-1, and the average voltage of the intercalation was in the range of 0.75-0.96 V. Therefore, 3R-MoS₂ is a very promising cathode material for AIBs.