Decoupling structure–performance relationships in hard carbon anodes: a comparative study of slope- and plateau-dominated sodium storage mechanisms

Abstract

Sodium-ion batteries (SIBs) have emerged as a promising candidate for large-scale energy storage applications due to their abundant resources, higher safety, and superior low-temperature performance. The development of advanced anode materials constitutes a fundamental research frontier in SIB technology, where hard carbon (HC) anodes are considered the most promising candidate for commercial implementation due to their balanced performance metrics. However, significant scientific challenges regarding precursor sustainability, structural controllability, and a precise understanding of sodium storage behavior remain. In this work, we established a comprehensive structure–property–performance relationship through rationally designed carbon architectures. Two distinct HC materials, slope-dominated (SD-HC) and plateau-dominated (PD-HC) hard carbons, were synthesized from a gluconate precursor. Through a multimodal characterization approach combining ex situ and in situ spectroscopic techniques, we elucidate the structure–property–performance relationships governing their divergent electrochemical behaviors. Our findings demonstrate that controlled carbonization enables precise regulation of hard carbon's pore architecture and interlayer spacing, thereby dictating the sodium storage behavior. While PD-HC achieves higher capacity via more closed pores, SD-HC exhibits a superior cycling stability of 137.4 mA h g⁻¹ over 3000 cycles at 3C, along with interfacial stability, positioning it as an ideal anode for durable sodium-ion batteries. These results provide a scientific foundation for the rational design of next-generation SIB hard carbon anodes.