Self-building sodium modified g-C₃N₄/CN for fast kinetics in sodium‑sulfur batteries by first-principles calculations

The development of triple-functional catalysts to inhibit the shuttle effect of polysulfide (NaPSs) and speed up the kinetics of charge-discharge events is crucial to advance the practical use of sodium‑sulfur batteries (NaSBs). However, the application of g-C₃N₄ and CN as sulfur hosts in NaSBs is hindered by their inherently low electrical conductivity and high energy barriers for Na⁺ migration. In this work, the density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations reveal that the Na atoms have a tendency to favor a "self-building" process, which result in the formation of Na@g-C₃N₄ and Na@CN after the initial discharge. Notably, within the Na-embedded substrates, the trapped Na effectively balances the polarity of the N₆ cavity, accompanied with a moderate binding with NaPSs and effective dissociation of Na₂S. Electronic structure analysis reveals that the incorporation of Na significantly enhances the electrical conductivity of g-C₃N₄/CN and creates efficient channels for Na⁺ diffusion. This promotes the transport of Na⁺ with lower migration energy barriers (0.61 and 0.69 eV) in Na@g-C₃N₄ and Na@CN, thereby accelerating the dynamic transformation and desorption of intermediates. Overall, this study offers new insights into the structural evolution mechanisms of g-C₃N₄ and CN, and provides valuable guidance for the subsequent design and experimental research of high-performance Na-S battery catalysts.