<p>Hard carbon (HC) as an anode material for sodium-ion batteries (SIBs) suffers from poor rate capability, low first-cycle coulombic efficiency, and insufficient cycle stability. To address these issues, HC is commonly modified via high-temperature sintering, hydrothermal synthesis, or gas-phase deposition; however, these methods often introduce impurities due to the use of additives. In this work, dielectric barrier discharge (DBD) plasma, a “clean modification” technique employing energetic particles, is utilized to simultaneously etch the carbon skeleton and dope nitrogen atoms onto the HC surface. By adjusting the modification time, the size of pseudo-graphitic microcrystals can be precisely controlled, while the energetic species generated by the DBD plasma facilitate the formation of nitrogen defects (N-defects). This strategy effectively tailors the pore structure and interfacial wettability of HC, thereby creating additional Na⁺ active sites and enhancing Na⁺ transport kinetics. As a result, the optimized HC-6 sample delivers a reversible capacity of 326.8 mAh g⁻¹ at 0.02 A g⁻¹, along with a capacity retention rate of 92.73% after 800 cycles under high-rate conditions (3 A g⁻¹). Compared with pristine HC, HC-6 exhibits a 14% increase in capacity and a 50% longer cycle life. This study provides valuable insights into the strategic design of HC surface architectures via plasma engineering and promotes the advancement of plasma-modified SIB materials.</p>