Performances of O- and S-functionalized Mo2C monolayer in lithium ion batteries: Theoretical and experimental research

MXenes exhibit outstanding potential as electrode materials for lithium-ion batteries (LIBs) due to their extensive specific surface area, superior electrical conductivity and abundant surface-active terminations. The electrochemical properties of Mo ₂CT ₂ (T = bare, -O, -S) as anodes for LIBs have been studied by adopting the first-principles calculations and experiments. The results reveal that Mo ₂CO ₂ has a negative impact on Li storage, leading to a slight decrease in theoretical capacity and a significant increase in average voltage. The low migration energy barriers of Mo ₂C, Mo ₂CO ₂ and Mo ₂CS ₂ are estimated as 0.037 eV, 0.145 eV and 0.244 eV. Moreover, the predicted average voltages of Mo ₂C and Mo ₂CS ₂ are 0.79 V and 0.11 V, rendering them highly desirable for low charging voltage applications. It is striking that the storage capacity of Mo ₂C is improved remarkably from 263 mA·h/g to 400 mA·h/g by introducing S functional group. Herein, experimental batteries are fabricated with Mo ₂CS _x and Mo ₂C as anodes to investigate their electrochemical properties, which exhibit both stability and reversibility. Interestingly, the exceptional discharge capacity and cycling stability of Mo ₂CS _x can be attributed to its unique structure, which is consistent with the calculated results. Therefore, S-decorated Mo ₂C is a more suitable anode for LIBs with excellent performance, which also provides guidance for introducing appropriate functional groups to enhance the electrode performance of other MXenes.