Regulation of microcrystalline and pore structures in pitch-based hard carbon via liquid-phase crosslinking-assisted grain boundary etching to enhance sodium storage performance†

Abstract

Heavy oils, known for their high carbonization yield, typically form highly ordered structures with narrow interlayer spacing of carbon layers during carbonization, which limits their sodium storage performance. To address this limitation, we propose a strategy that modifies the carbonization pathway by coupling liquid-phase crosslinking with K₂CO₃ activation. This approach effectively modulates the microcrystalline state and pore structure while inhibiting the growth and orientation of crystal domains. During the liquid-phase crosslinking of raw materials, oxygen radicals would mediate the formation of non-planar macromolecules with a highly reactive cross-linked structure. This structure would induce the formation of numerous defect sites within the carbon layers during K₂CO₃ activation, which, through a synergistic enhancement of etching around the boundary of carbon-layer stacks, effectively prevents the fusion and growth of stacks. Consequently, the graphite-like microcrystals formed during the carbonization process exhibit a random orientation. Additionally, the vacancy defects within the carbon layers are prone to inducing layer bending at high temperatures of carbonization, which contributes to the formation of closed pores, particularly when the carbon layers are of moderate size. As a result, the optimized sample (HC325) maintains a high reversible capacity of 328.3 mA h g⁻¹ after 200 cycles at a current density of 100 mA g⁻¹, with the plateau capacity accounting for up to 68%. This study provides novel insights into the modulation of the carbon microcrystalline structure and pore architecture of pitch-based hard carbon, offering guidance for the development of high-performance hard carbon anodes.