The article reports the use of expanded graphite (EG) as a superior anode material for sodium-ion batteries (NIBs). Traditional graphite, the most common anode material for lithium-ion batteries (LIBs), has a low capacity when used in NIBs due to insufficient interlayer spacing for Na⁺ insertion. EG, prepared through a two-step oxidation-reduction process on graphite, retains a long-range-ordered layered structure with an enlarged interlayer distance of 4.3 Å, which allows reversible Na⁺ insertion and extraction. In situ transmission electron microscopy (TEM) confirms the reversible microstructural changes during the sodiation and desodiation processes. Electrochemical tests show that EG delivers a high reversible capacity of 284 mAh g⁻¹ at 20 mA g⁻¹, maintains a capacity of 184 mAh g⁻¹ at 100 mA g⁻¹, and retains 73.92% of its capacity after 2,000 cycles. These findings position EG as a promising anode material for NIBs, offering a low-cost and sustainable alternative to graphite in large-scale energy storage applications.The article reports the use of expanded graphite (EG) as a superior anode material for sodium-ion batteries (NIBs). Traditional graphite, the most common anode material for lithium-ion batteries (LIBs), has a low capacity when used in NIBs due to insufficient interlayer spacing for Na⁺ insertion. EG, prepared through a two-step oxidation-reduction process on graphite, retains a long-range-ordered layered structure with an enlarged interlayer distance of 4.3 Å, which allows reversible Na⁺ insertion and extraction. In situ transmission electron microscopy (TEM) confirms the reversible microstructural changes during the sodiation and desodiation processes. Electrochemical tests show that EG delivers a high reversible capacity of 284 mAh g⁻¹ at 20 mA g⁻¹, maintains a capacity of 184 mAh g⁻¹ at 100 mA g⁻¹, and retains 73.92% of its capacity after 2,000 cycles. These findings position EG as a promising anode material for NIBs, offering a low-cost and sustainable alternative to graphite in large-scale energy storage applications.