<p>Hard carbon is widely regarded as a promising anode material for sodium-ion batteries owing to its high reversible capacity and low operating potential. Nevertheless, achieving an optimal balance between electrochemical performance and cost-effectiveness remains a significant challenge. In this study, spent coffee grounds (SCGs) were employed as a sustainable precursor for the synthesis of hard carbon via a pre-oxidation-assisted high-temperature carbonization process. The influence of pre-oxidation on the structural evolution and sodium storage behavior of the resulting materials was systematically investigated. Experimental results indicate that pre-oxidation effectively introduces abundant oxygen-containing functional groups, suppresses excessive graphitization and structural ordering of carbon microcrystallites, enlarges the interlayer spacing (d₀₀₂), and facilitates the formation of a turbostratic structure with closed micropores. The sample subjected to pre-oxidation at 300&#xa0;°C followed by carbonization at 1200&#xa0;°C exhibits superior electrochemical performance, delivering a high reversible specific capacity of 328.49 mAh g^− 1, excellent cycling stability with Coulombic efficiency stabilized at 97–98%, and outstanding rate capability. This work not only presents a novel strategy for the valorization and resource recovery of waste coffee grounds but also underscores the critical role of pre-oxidation in tailoring the microstructure of biomass-derived hard carbons, thereby enhancing their performance in sodium-ion batteries. These findings offer valuable insights for the development of low-cost, sustainable, and high-performance energy storage materials.</p> Graphical Abstract <p></p>