Precision structural modulation and sodium cluster operando presodiation for high-performance hard carbon anode with fast kinetics in sodium-ion batteries

The presence of long-range ordered carbon with narrow interlayer distances and the deficiency of appropriate size closed pores in hard carbon impede effective Na + intercalation and filling, constraining its low-voltage plateau and plateau kinetics. Moreover, hard carbon is compromised by an unstable solid-electrolyte interphase (SEI) and diminished initial Coulombic efficiency (ICE). This work pioneers an innovative approach by employing sodium acetate nanopore templates to meticulously engineer the pore architecture and crystal structure at the molecular level, simultaneously achieving operando presodiation. The templates effectively modify phenolic resin-derived carbon phase by simultaneously generating closed nanospaces and hierarchical porosity, while restraining long-range carbon sheets growth. Importantly, the sodium clusters formation that originate from Na 2 O disintegration during high temperature pyrolysis and are implanted into the closed nanopores play a crucial role in compensating for irreversible Na loss and effectively lowering Na + migration barrier. The surface-bound residual Na 2 CO 3 and Na 2 O on hard carbon induce formation of a robust NaF-rich SEI. Consequently, the hard carbon achieves an exceptional reversible capacity of 422 mAh g −1 at 0.1 C with a high ICE of 93 %, along with an outstanding rate capability of 325 mAh g −1 at 10 C. This work guides constructing superior hard carbon anodes and probes into the presodiation mechanism.