Pitch composition-guided pore-closing engineering of commercial activated carbon for sodium storage

The development of sodium-ion batteries is constrained by the lack of high-performance, low-cost anodes, where hard carbon (HC) often suffers from trade-offs in capacity, initial Coulombic efficiency (ICE), and cost due to poorly controlled porosity. To overcome this, we propose a pitch composition-guided pore-closing engineering strategy. By employing commercial activated carbon (with inherent open pores) as a low-cost precursor and petroleum pitch as a tunable pore‑closer, we demonstrate that the chemical composition of pitch critically governs the pore-closing efficiency during pyrolysis. It is revealed that the large-molecular components in pitch readily stack at the entrances of open pores after pyrolysis, thereby enabling the desired pore closure. In contrast, small-molecular components tend to deposit within the pores, reducing the closed-pore volume and compromising sodium storage capacity. The HC derived from pitch with minimal small-molecular components delivers a reversible capacity of 292 mAh g −1 and an ICE of 87.4% in an ester-based electrolyte. Kinetic analysis reveals that this enhanced storage behavior proceeds via an adsorption-filling mechanism, where the slope capacity arises from Na + adsorption on surfaces and defects, and the plateau capacity originates from the filling of closed pores. When assembled into 18650 cylindrical cells with a NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode, the cell retains over 95% capacity after 200 cycles at a charge-discharge C-rate of 5C/5C. This work provides fundamental insight into pore-structure regulation and offers a practical strategy for designing high-performance HC anodes from economical precursors.