Carbonyl-functionalized PVAC binder stabilizes hard carbon anodes via interfacial passivation for high-initial-coulombic efficiency Na-ion storage

Hard carbon for sodium-ion batteries suffers from interfacial instability caused by irreversible sodium loss and electrolyte decomposition at defective sites, leading to rapid degradation of initial coulombic efficiency and cycling stability. While conventional polymer binders struggle to simultaneously stabilize interfacial electrochemistry and maintain electrode mechanical integrity under dynamic volume changes. To address this challenge, we propose a carbonyl-functionalized polyvinyl acetate (PVAC) binder to modulate hard carbon-electrolyte interactions. Coupling PVAC with hard carbon synthesized via controlled pyrolysis of phenolic resin precursors enables C=O-mediated defect passivation and interfacial optimization. PVAC-based electrode forms a 10 nm-thick inorganic-dominant solid electrolyte interphase composed of Na 2 CO 3 and NaF, achieving a high initial coulombic efficiency of 85.1 %, while the polyvinylidene fluoride (PVDF) based electrode only reached 65.9 %. Dynamic hydrogen-bonding networks of PVAC mitigate mechanical stress during sodiation, and its ester groups regulate Na + solvation structures, reducing charge transfer resistance to 2.5 Ω. This electrode retains 322.5 mAh g −1 after 100 cycles at 0.05 A g −1 and delivers 289 mAh g −1 at 1 A g −1 . This work establishes molecular engineering principles for multifunctional binders that synergistically balance interfacial stability and electrode mechanics, achieving sodium-ion battery anodes with high initial coulombic efficiency. • PVAC enables 85.1 % initial efficiency in hard carbon anodes. • PVAC induces a 10 nm-thick, inorganic-rich SEI layer. • PVAC passivates defects and facilitates Na + transport. • The anode retains 289 mAh g −1 after 1000 cycles at 1 A g −1 .