Tuning Hard Carbon Pores at the Ångstrom Scale Facilitates Sodium‐Ion Pre‐Desolvation in High‐Performance Sodium‐Ion Batteries

ABSTRACT Hard carbon (HC) is a promising sodium‐ion battery (SIBs) anode material but suffers from unstable solid electrolyte interphase (SEI) formation, low initial Coulombic efficiency (ICE), and limited capacity. These issues are intrinsically linked to the pore mouth size and Na⁺ active sites of HC. In this work, we developed a novel hard carbon (S‐HC‐2) through Ångstrom‐scale engineering of the pore mouths to under 3.5 Å, while simultaneously incorporating abundant sodium storage sites. This promotes the pre‐desolvation of Na + prior to pore entry, while facilitating the formation of highly aggregated electrolyte within pores. As a result, an ultra‐thin and NaF‐rich SEI is achieved. The optimized S‐HC‐2 electrode delivers a remarkable reversible capacity of 474.8 mAh/g and an ultrahigh ICE of 92.6%. (vs. 300 mAh/g and 84.2% ICE of commercial K‐HC). Even after 920 cycles at 1 A/g (about 3 C rate), the S‐HC‐2 maintained 100% capacity, demonstrating far superior cycling stability compared to K‐HC. The S‐HC‐2//Na 3 V 2 (PO 4 ) 3 full‐cell demonstrated excellent performance, achieving a high initial capacity (105 mAh/g) and outstanding cycling stability (94.8% capacity retention) over 300 cycles. Our work provides new insights for preparing HC with high specific capacity and ICE at the Ångstrom scale, accelerating the commercialization of SIBs.