Vacancy engineering and electronic structure modulation in 2D Ta2Se2C for enhanced alkali-ion batteries

Two-dimensional transition metal carbon-chalcogenides have emerged as promising candidates for energy storage applications; however, understanding the role of intrinsic point defects on their electrochemical performance remains critical. Herein, we systematically investigate the structural stability, electronic properties, and alkali-metal (Li/Na) storage behaviors of pristine, carbon-vacant (V C ), and selenium-vacant (V Se ) Ta 2 Se 2 C monolayers using first-principles density functional theory (DFT) calculations. Both defective configurations maintain metallic conductivity and structural integrity. Alkali adsorption calculations demonstrate enhanced binding affinities on the defective substrates, with negative adsorption energies that prevent metal clustering. The calculated average open-circuit voltages (0.1–0.8 V) remain safely above 0 V vs. Li/Li + (Na/Na + ), mitigating metallic plating risks while sustaining a high operational cell voltage. Kinetic analysis reveals that while the pristine monolayer exhibits moderate diffusion barriers, the selenium vacancy (V Se ) facilitates Na + transport along a specific migration channel (path P5), yielding a localized diffusion coefficient of ∼10 −3 cm 2 s −1 compared to ∼10 −5 cm 2 s −1 for conventional pathways. Furthermore, ab initio molecular dynamics (AIMD) simulations confirm the thermal and mechanical resilience of maximum-adsorption configurations, showing minimal in-plane lattice swelling (≤1.78% in defective vs. 3.05% in pristine). These findings demonstrate that vacancy engineering provides site-selective kinetic modulation and strain buffering, offering critical design guidelines for robust 2D anode materials in next-generation Li/Na-ion batteries.