Constructing carbonyl interface and closed pore structure via oxidative crosslinking in starch-derived hard carbon for enhanced sodium storage

• Oxidative cross-linking strategy to modulate closed pore content. • C O functional group preferentially catalyzes salt decomposition to form inorganic component-rich solid electrolyte interface. • Optimized sample with excellent plateau capacity and initial coulombic efficiency. • Validation of adsorption, intercalation, and pore-filling mechanism for sodium storage. Hard carbon (HC) with abundant closed pores and inorganic-rich interfaces is the key to keep superior electrochemical properties for sodium-ion batteries (SIBs), while the simple and effective regulation strategies still need to be further developed. Herein, based on the strategy of crosslinking, a pitch additive is introduced to the synthesis of starch-derived HC, which can cross-link to the surface of starch granules as an isolation layer, retarding the gas generation to alleviate starch foaming during pyrolysis. Most importantly, the use of pitch promotes the conversion of OH groups in starch into C O groups rather than water and carbon dioxide. The oxygen-containing groups hinder the orderly rearrangement of carbon layers and in turn distort and fold to form a large number of closed pores. Furthermore, C O groups are able to catalyze the preferential reduction of electrolyte anions to induce fluorine-rich solid electrolyte interface (SEI). As a result, the optimized HC exhibits a high initial coulombic efficiency (ICE) of 93 % and a reversible capacity of around 336 mAh g −1 at a current density of 30 mA g −1 . This work sheds light on the construction of high-performance HC anode with regulating the carbonization procedure and interface chemistry.