Ti4C3 and Ti4N3 MXenes: ultrafast Na-ion diffusion and figure-of-merit benchmarking for sodium-ion battery anodes

• Ti 4 C 3 and Ti 4 N 3 MXenes exhibit ultralow Na-ion migration barriers (0.049 and 0.028 eV). • Multiple stable Na adsorption sites enable uniform Na accommodation and suppress Na clustering. • –F termination preserves key anode descriptors; –O/–OH terminations show favorable Na adsorption in screening tests. • A generalized figure of merit integrates capacity, OCV, and diffusion barrier for direct benchmarking of 2D anodes.