Transformative Catalytic Carbon Conversion Enabling Superior Graphitization and Nanopore Engineering in Hard Carbon Anodes for Sodium-Ion Batteries

Abstract

Hard carbons are promising anode materials for sodium-ion batteries (SIBs), but they face challenges in balancing rate capability, specific capacity, and initial Coulombic efficiency (ICE). Direct pyrolysis of the precursor often fails to create a suitable structure for sodium-ion storage. Molecular-level control of graphitization with open channels for Na+ ions is crucial for high-performance hard carbon, whereas closed pores play a key role in improving the low-voltage (< 0.1 V) plateau capacity of hard carbon anodes for SIBs. However, creation of these closed pores presents significant challenges. This work proposes a zinc gluconate-assisted catalytic carbonization strategy to regulate graphitization and create numerous nanopores simultaneously. As the temperature increases, trace amounts of zinc remain as single atoms in the hard carbon, featuring a uniform coordination structure. This mitigates the risk of electrochemically irreversible sites and enhances sodium-ion transport rates. The resulting hard carbon shows an excellent reversible capacity of 348.5 mAh g−1 at 30 mA g−1 and a high ICE of 92.84%. Furthermore, a sodium storage mechanism involving “adsorption–intercalation–pore filling” is elucidated, providing insights into the pore structure and dynamic pore-filling process.