A method for preparing a Li4NbxTi5-xO12/C nanocomposite as anode material for lithium-ion batteries is disclosed, which includes the following steps: (a) obtaining a mixture of a lithium salt, niobium pentaoxide, titanium dioxide (TiO2), and a carbon source in a selected stoichiometric ratio; (b) mixing the mixture in a dispersant to produce a slurry; (c) drying the slurry to produce a dried mixture; (d) treating the dried mixture under a protective atmosphere, according to a heating program to produce the Li4NbxTi5-xO12/C nanocomposite, wherein the heating program comprises: calcining the dried mixture at 600° C. for 2-6 hours, heating it at a rate of 2-20° C. per minute to 950-980° C., cooling it by natural cooling to 800-850° C., maintaining the temperature at 800-850° C. for 16 hours, and cooling it by natural cooling to room temperature.