Unveiling High Capacity and Fast Sodium Diffusion in Ti ₂ C/Sn ₄ P ₃ /Ti ₂ C Anode for Sodium-Ion Batteries via Density Functional Theory and Ab Initio Molecular Dynamics Simulation

Sodium-ion batteries (SIBs) represent a compelling alternative to lithium-ion batteries (LIBs) for sustainable energy storage, addressing critical LIB limitations, such as high cost, thermal runaway risks, poor low-temperature performance, and resource sustainability concerns. To realize the potential of SIBs, developing advanced anode materials is crucial. This study introduces a novel Ti2C/Sn4P3/Ti2C heterostructure anode with a sandwich architecture, ingeniously integrating conductive two-dimensional Ti2C MXene with high-capacity layered Sn4P3 phosphide. Through comprehensive density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, we elucidate the electronic structure, sodium-ion storage mechanism, and diffusion kinetics at the heterointerface. The results reveal that robust Sn–P–Ti interfacial bonding significantly enhances the conductivity and dramatically accelerates sodium-ion diffusion. The AIMD-calculated migration barrier is as low as 0.14 eV, indicating that the unique 3D network and cooperative multi-ion dynamics facilitate ultrafast diffusion. Crucially, the heterostructure design substantially boosts the theoretical sodium storage capacity to 714 mAh/g, representing a 37% increase over the pristine Sn4P3 monolayer and surpassing materials like sodium titanate or manganese oxide. The Ti2C/Sn4P3/Ti2C heterostructure possesses several key attributes: a high theoretical capacity, an exceptionally low diffusion barrier, and an enhanced interfacial stability. These combined features make it a highly promising anode candidate for next-generation sodium-ion batteries. This work also provides a new theoretical framework for designing high-performance SIB anodes through rational interface engineering.