Single-vacancy engineering of blue phosphorene for suppressing the shuttle effect and enhancing conversion kinetics in Na-Se batteries: A computational investigation

The development of high-performance sodium-selenium (Na-Se) batteries is critically hindered by the dissolution and migration of intermediate polyselenide species, which induce severe shuttle effects and degrade cycling stability. In this work, first-principles density functional theory calculations are employed to systematically investigate single-vacancy blue phosphorene (SVBlueP) as an effective host material for sodium polyselenides. The structural stability, adsorption behavior, electronic properties, charge-transfer characteristics, and reaction thermodynamics and kinetics of Na 2 Se n (n = 1, 2, 4, 6, 8) species on SVBlueP are comprehensively analysed. The results reveal that introducing single-vacancy defects significantly enhances polyselenide binding through higher interfacial charge transfer and orbital hybridization, while preserving the metallic character of the host surface. Charge density difference and Bader analyses confirm pronounced electron donation from Na 2 Se n clusters to the vacancy phosphorene surface, indicative of chemisorption-dominated interactions, particularly for low-order polyselenides. Electron localization function analysis further demonstrates the coexistence of covalent and ionic bonding characteristics, rationalizing the observed adsorption strength hierarchy. Thermodynamic calculations show that SVBlueP markedly lowers the Gibbs free energy along the Na-Se conversion pathway relative to the vacuum reference, thereby promoting favorable polyselenide transformation reactions. In addition, climbing image nudged elastic band calculations reveal a substantially reduced energy barrier for Na 2 S decomposition on SVBlueP, highlighting its catalytic role in accelerating electrochemical kinetics. These findings elucidate the critical role of vacancy-induced surface electronic modulation in regulating polyselenide adsorption and conversion and establish single-vacancy blue phosphorene as a promising surface-engineered host for mitigating shuttle effects and enhancing the performance of Na-Se batteries.