Tailoring closed pore content of starch-modified phenolic resin to enhance plateau capacity of hard carbon anodes for sodium-ion batteries

Sodium-ion batteries (SIBs) are garnering significant attention as a highly attractive alternative to lithium-ion batteries. The widespread application of SIBs is limited by the unsatisfactory capacity observed in the low-voltage plateau region and insufficient initial Coulombic efficiency (ICE). Herein, starch-modified phenolic resin-based hard carbon (SR-HC) is developed as a high-performance anode for SIBs via a two-step carbonization process. The crosslinking reaction significantly increases the closed pore content, which will improve the plateau capacity. The optimal SR-HC anode exhibits an initial discharge capacity of 381.2 mAh g −1 , achieves a high ICE of 87.1%, and maintains 95.4% of its capacity after 100 cycles. Importantly, the plateau capacity reaches 262.7 mAh g −1 , accounting for 69.1% of the total capacity. The excellent electrochemical performance of SR-HC is attributed to crosslinking, and the underlying mechanism and structure-performance relationship are elucidated. These findings demonstrate that the plateau capacity can be fundamentally enhanced through the simple crosslinking of resin and starch, which further advances its industrialization potential.