Achieving Enhanced Sodium Storage Performance of Hard Carbon via Rational Modification of a Starch Precursor

Chemical modification of starch hydroxyl groups plays a key role in modulating the microstructures and enhancing the electrochemical performance of the hard carbon (HC) anode in sodium-ion batteries (SIBs). However, the regulation and design of advanced sodium storage structures are limited by their diverse and complex microstructures. Herein, diammonium phosphate (DAP) as a cross-linking agent for corn starch and modification of the physicochemical properties of the starch surface can effectively promote the regulation and balance between the pore structure and interlayer spacing of the constructed HC. The electrochemical performance of modified HC generally outperformed that of unmodified HC samples. Specifically, the optimized HC-10 achieved an improved reversible capacity (344.16 mAh g^-1 at 0.03 A g^-1), optimal rate capability (134.73 mAh g^-1 at 0.3 A g^-1), and enduring cycle life (capacity retention of 98.5% after 500 cycles at 0.3 A g^-1). The superior performance of HC-10 originated from the optimal modification operation of DAP for corn starch, resulting in a balance between the formation of disordered phases and pore structures. On the one hand, the DAP facilitates the growth of the carbon layers during pyrolysis and affects the microinterlayer structure of HC, while it also accelerates the decomposition of the precursor as a catalyst and releases gas phase products, which further modulate the defects and pore structures of HC. This work provides a reference for the microstructural regulation of HC, paving the way for the development of biomass-derived anode materials with exceptional charge/discharge performance.