Pore Architecture Tailoring of Resin-Based Hard Carbons: A Synergistic Closed–Open-Pore Network for Fast Plateau Kinetics in Sodium-Ion Batteries

Hard carbon is widely considered a leading anode candidate for sodium-ion batteries (SIBs) because of its high reversible capacity and low operating potential. However, simultaneously achieving high capacity, high initial Coulombic efficiency (ICE), and high-rate performance necessitates precise control over the microstructure of hard carbon, particularly its complex pore architecture. Herein, we propose a pore-tailoring strategy that utilizes mesopores to facilitate the escape of gaseous decomposition products, thereby regulating whether the hard carbon is dominated by open or closed pores. Using phenolic resin as a carbon precursor and F127 as a mesopore-forming agent, three hard carbon samples with distinctly different open/closed-pore architectures are successfully synthesized. Systematic microstructural characterization demonstrates that the proposed pore-tailoring strategy has little to no effect on the interlayer spacing of the resulting hard carbon. Consequently, the hard carbon sample featuring a synergistic open–closed-pore network exhibits an optimal combination of properties: a high initial discharge capacity of 372.7 mA h g –1 at 20 mA g –1 with an ICE of 86.83% and remarkable rate and cycling stability, i.e., retaining 145.0 mA h g –1 at 5000 mA g –1 after 1200 cycles with a fade rate of only 0.03% per cycle. Further kinetic studies and in situ characterization were conducted to elucidate the electrochemical advantages and sodium storage mechanism, revealing that the developed open–closed-pore network enables fast plateau kinetics. This work clarifies how the mesoporous structure regulates the closed–open-pore structure in hard carbon and provides a strategic approach for designing high-performance hard-carbon anodes for SIBs.