Construction of hard carbon with abundant closed ultra-micropores via a pre-oxidation strategy for high-efficiency sodium storage in the low potential plateau

Abstract

Rationally regulating the porosity of hard carbon (HC), especially the closed pores matching the low potential plateau and the ultra-microporous structure suitable for Na⁺ embedding, has been shown to be the key to improving the sodium storage performance and initial coulombic efficiency (ICE). However, the preparation of such HC materials with specific pore structures still faces great challenges. Herein, a simple pre-oxidation strategy is employed to construct abundant closed ultra-microporous structures in soy protein powder-derived HC material, achieving a significant improvement in its ICE and platform capacity. The pre-oxidation process promotes the cross-linking degree of the soy protein, thereby hindering the directional growth of graphite domains during the carbonization process. The optimized HC exhibits ultra-high platform capacity (329 mAh g⁻¹) and considerable energy density (148.5 Wh kg⁻¹). Based on the ex-situ Raman and X-ray photoelectron spectroscopy characterization results, the excellent sodium storage capacity of the HC material is attributed to the synergistic effect of adsorption-intercalation/filling. The presented work provides novel insights into the synthesis of other biomass-derived HC materials with abundant closed ultra-micropores.