Spatial Structural Self-Regulation Engineering Increases Close Pores of Starch-Derived Hard Carbon for Sodium-Ion Batteries

Abstract

Starch, a sustainable precursor for hard carbon (HC) in sodium-ion batteries (SIBs), faces challenges of low carbon yield (~10%), foaming, and excessive graphitization during carbonization. Herein, a unique spatial structural self-regulation strategy is proposed to precisely program the microstructure of starch-derived HC with the pre-oxidation method, transforming its helical chains into a robust, three-dimensional cross-linked framework. This strategy regulates microstructure evolution by inducing self-carbonylation of hydroxyl groups, suppressing foaming and graphitization, and controlling pore evolution at the molecular level to form closed-pore-encoded carbon microdomains. The resulting material achieves a carbon yield of 26%, a 2.6-fold improvement, and a high-density closed-pore structure. Resultantly, CS-O-1400 delivers 385 mAh g⁻¹ reversible capacity, 92.36% initial Coulombic efficiency (ICE), and 278 mAh g⁻¹ rate capability at 2 A g⁻¹. Furthermore, in situ Raman and electron paramagnetic resonance (EPR) technologies jointly reveal that HC with short-range graphitic crystallites triggers intercalation-dominated sodium storage while synergistically coordinating adsorption and pore-filling mechanisms, forming a marked contrast to the stepwise reaction sequence observed in long-range graphitic crystallite configurations. This work demonstrates that spatial structural self-regulation engineering is a simple and efficient approach to optimizing the electrochemical performance of HC for SIBs.

Keywords

closed pore / hard carbon / self-carbonylation / sodium-ion battery / spatial structural self-regulation

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