Precise anchoring of pre-oxidation sites via Zn–O–C chemical bonding for enhanced sodium storage in pitch-derived hard carbon

Abstract

Against the backdrop of global carbon neutrality, sodium-ion batteries (SIBs) have emerged as a pivotal technology for large-scale energy storage, benefiting from the abundance and low cost of sodium. However, the development of low-cost, high-performance anode materials remains a critical bottleneck. Pitch, a byproduct of petroleum refining, is an ideal precursor for hard carbon anodes due to its high availability and carbon yield. Nevertheless, low-softening-point pitch tends to undergo severe melting and agglomeration during conventional pre-oxidation, leading to inhomogeneous oxidation and excessive ordered stacking of carbon layers, which significantly restricts its sodium storage performance. Herein, we develop a green and energy-efficient Zn–O–C chemical crosslinking-assisted pre-oxidation strategy. By incorporating low-toxicity zinc acetate via liquid-phase blending at the molecular level, Zn–O–C coordination bonds are formed, which precisely anchor the pre-oxidation sites and fundamentally suppress the melting of pitch. The resultant hard carbon features a highly disordered structure, expanded interlayer spacing, and a large number of ultramicropores. It achieves a reversible capacity of 322 mAh g⁻¹ at 30 mA g⁻¹, along with a significantly enhanced low-voltage plateau capacity, outstanding rate capability, and excellent cycling stability. Combined in situ characterizations and density functional theory calculations reveal an “adsorption–intercalation–pore filling” sodium storage mechanism. Notably, this strategy incurs no additional energy consumption compared to conventional processes while enabling high-value valorization of an industrial byproduct, offering a sustainable route for the preparation of hard carbon anodes.