Coupled sub-Nanometer pore-entrance confinement and carbonyl functionalization regulate desolvation-selective solid electrolyte interphase formation in hard carbon anodes

Both pore-entrance size and C=O-containing surface species critically influence solid electrolyte interphase (SEI) formation in hard carbon, whereas their synergistic effect has remained largely unexplored. Herein, a CO₂-etching strategy is employed to regulate the pore-entrance size and CO content of hard carbon with the aim of tailoring SEI formation. Systematic characterizations show that the pore-entrance size gradually decreases with increasing etching time, while the relative CO content first increases and then decreases. Notably, when the pore-entrance size is larger than 0.35 nm, SEI formation is mainly governed by pore structure; once the pore-entrance size is reduced below 0.35 nm, the CO content becomes the dominant factor determining SEI chemistry. Consequently, through the synergistic regulation of pore-entrance confinement and CO surface species, the optimized sample with a pore-entrance size below 0.35 nm and a high CO proportion (65.7%) forms a thinner (≈11 nm) and more uniform SEI, achieving a high initial Coulombic efficiency of 87.2%. Meanwhile, the improved interfacial stability and accelerated ion transport kinetics also endow the electrode with enhanced rate performance and prolonged cycling life over 1500 cycles. This work offers a new design strategy for regulating SEI formation by integrating pore-structure engineering with oxygen-related interfacial chemistry.