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 Mo2CT2 (T = bare, -O, -S) as anodes for LIBs have been studied by adopting the first-principles calculations and experiments. The results reveal that Mo2CO2 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 Mo2C, Mo2CO2 and Mo2CS2 are estimated as 0.037 eV, 0.145 eV and 0.244 eV. Moreover, the predicted average voltages of Mo2C and Mo2CS2 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 Mo2C is improved remarkably from 263 mA·h/g to 400 mA·h/g by introducing S functional group. Herein, experimental batteries are fabricated with Mo2CSx and Mo2C as anodes to investigate their electrochemical properties, which exhibit both stability and reversibility. Interestingly, the exceptional discharge capacity and cycling stability of Mo2CSx can be attributed to its unique structure, which is consistent with the calculated results. Therefore, S-decorated Mo2C 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.