A search for high-efficiency electrode materials is crucial for the application of Li-ion batteries (LIBs). Using density functional theory (DFT), we assess the Mn2C sheet, a new MXene, as a suitable electrode material. Our studies show that Li atoms can bind strongly to the Mn2C sheet, with low adsorption energy of −1.93eV. A pristine Mn2C sheet exhibits metallic characteristic, offering an intrinsic advantage for the transportation of electrons in material. A very low energy barrier of 0.05eV is predicted, showing that Li ion can easily and freely migrate on the Mn2C sheet. In addition, with the increase of Li content, adsorption energy varies minimally within a range of energy that spans only 0.27eV, showing that lithiation to a high content is feasible. Furthermore, we found that, because of the bilayer adsorptions on both sides of the Mn2C sheet, the theoretical capacity of the Mn2C sheet is 879mAhg−1, which is greater than that of most two-dimentional (2D) electrode materials. All these results reveal a new promising MXene material for LIBs. We also studied the effects of oxidation and fluorination on the electrochemical properties of the Mn2C sheet and found that oxidation and fluorination will fade the electrochemical properties of the Mn2C sheet in general.