Metal coordination strategy to control the pore structure of hard carbon materials for high-performance sodium storage

Abstract

Hard carbon is a promising anode for sodium-ion batteries, yet regulating its pore structure remains key to enhancing performance. Herein, we report a coordination modulation strategy using zinc acetate with a polyaniline precursor, followed by pyrolysis at 1300 °C to synthesize Zn-modified hard carbon (Zn-HC). The key is that Zn²⁺ first coordinates with –NH– groups along the chains, ensuring uniform dispersion prior to carbonization. This coordination regulates the local carbon structure and pore architecture, promoting closed pore formation. Simultaneously, zinc migration and volatilization create vacancies and oxygen defects, while facilitating increased graphitization. Through ex situ XPS and Raman analysis, the coordination mechanism and sodium storage processes in different voltage ranges are elucidated. The optimized Zn-HC anode delivers a high reversible capacity of 313.6 mAh g⁻¹ at 0.05 A g⁻¹ and maintains 190.3 mAh g⁻¹ at 2 A g⁻¹. It also exhibits excellent rate capability and long-cycle stability, retaining 75.1% capacity after 1000 cycles at 1 A g⁻¹. Distinct from sacrificial template methods, this strategy enhances capacity while simplifying synthesis, offering a promising route for scalable production of microstructure-optimized hard carbon.