Oxygen Functionalization Enables Magnesium Storage in a TiC3 Monolayer: A First-Principles Study of Mg Adsorption and Migration

Magnesium-ion batteries motivate the search for lightweight hosts with favorable storage energetics and accessible migration paths. We used density-functional theory to study Mg adsorption and migration on pristine and oxygen-functionalized TiC3. Adsorption on the pristine sheet is unfavorable relative to bulk Mg (+0.67 eV), whereas an isolated Mg atom binds at the B2 surface site of the partially oxidized sheet at –0.39 eV. For the sampled configurations, the PBE loading hull follows n = 0 → 1 → 4 → 12, where n is the number of Mg atoms in the Ti16C48O4 cell. The n = 12 endpoint gives a theoretical host-mass capacity of 457 mAh g–1, with voltage plateaus of 0.358, 0.249, and 0.014 V. Dispersion-inclusive relaxation retains a positive n = 4 → 12 insertion voltage, although its value depends on the treatment. Seven-image CI-NEB calculations give dilute B2–B3 surface barriers of 0.699 eV for the O-adjacent P1 path and 1.074 eV for the surface-void P6 path. These results show how oxygen functionalization changes Mg adsorption and the local migration environment. The low anode voltage and moderate dilute migration barrier should be considered together when assessing this model host.