Abstract: Sodium-ion batteries (SIBs) have become the promising grid energy storage due to their advantages such as abundant sodium resources, low cost, and similar electrochemistry and fabricated processes to that of widely commercialized lithium-ion batteries. Hard carbon, particularly biomass-derived hard carbon, is widely recognized as the most commercially viable anode material for SIBs, owing to its renewable precursors, low manufacturing cost, and suitable interlayer spacing for sodium ion storage. However, its practical application is severely hindered by inherent limitations, including poor rate capability, unsatisfactory cycling stability, low initial Coulombic efficiency (ICE), and an incomplete understanding of how pore structures (especially closed pores) govern sodium storage behavior. According to previous research, the sodium storage performance of biomass hard carbon can be regulated by parameters such as pore structure, interlayer spacing, defects, and oxygen content. However, the influence of closed-pore structure on its sodium storage behavior remains poorly understood. In this study, a dual-modification strategy is proposed combining sulfuric acid etching and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) selective pore engineering to tailor the microstructure of hard carbon derived from macadamia nut shells, aiming to address the above challenges. Structural characterizations reveal that sulfuric acid etching effectively removes impurities and dissolves cellulose components, constructing an open porous framework that facilitates mass transport. Subsequent PTCDA modification further optimizes the carbon microstructure by enhancing the ordering of carbon layers, reducing oxygen-containing defects, and constructing a well-balanced pore system (including closed pores and mesopores) that favors both sodium ion adsorption and intercalation. The resulting PTCDA-modified hard carbon (PTCDA-HC) exhibits enlarged interlayer spacing, high sp2 carbon content, and reduced oxygen defects, alongside a significantly improved carbonization yield compared to pristine and acid-treated counterparts. Electrochemical evaluations demonstrate that the PTCDA-HC delivers exceptional sodium storage performance. In half-cell tests, it achieves a high initial reversible capacity of 364.3 mAh·g-1 at 30 mA·g-1 with an ICE of 64.6%, retaining 90.5% of its capacity after 80 cycles. At a high current density of 300 mA·g-1, the modified electrode maintains 82.5% capacity retention over prolonged cycling, outperforming both pristine and acid-treated hard carbon. Kinetic analyses confirm enhanced sodium ion diffusion kinetics and a higher capacitive contribution in PTCDA-HC, accounting for its superior rate performance. When paired with a Na3V2(PO4)3 cathode, the full cell exhibits stable cycling, retaining a discharge capacity of 87.8 mAh·g-1 with 87.7% capacity retention and a Coulombic efficiency of ~98.5% after 100 cycles at 500 mA·g-1. This study not only provides a feasible strategy for regulating the microstructure of biomass-derived hard carbon anodes but also clarifies the structure-activity relationship between pore engineering and sodium storage behavior. The findings offer new insights into the high-value utilization of agricultural waste and the development of low-cost, high-performance hard carbon anodes for advanced SIBs.

Key words: Sodium-ion batteries, Anode, Macadamia Shell-derived hard carbon, Structural modification; sodium storage mechanism