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Ball milling modification endows the expanded graphite with smaller grain size and smaller specific surface area. The increase of defects is beneficial for the adsorption of potassium ions on the surface of expanded graphite. In situ XRD demonstrated that defects promote the staging reaction, resulting in higher potassium ion intercalation voltage, slower diffusion kinetics, and more thorough stage mechanism. [Display omitted] • Ball milled samples indicate that defects are beneficial for the insertion of potassium ions between graphite layers, promoting the progress of stage reactions. • The thorough stage reactions provide the sample with superior capacity and rate performance. • The diluted stage reacts at a relative higher voltage promoted by defects, resulting in higher average voltages for defect-rich sample. Expanded graphite (EG) stands out as a promising material for the negative electrode in potassium-ion batteries. However, its full potential is hindered by the limited diffusion pathway and storage sites for potassium ions, restricting the improvement of its electrochemical performance. To overcome this challenge, defect engineering emerges as a highly effective strategy to enhance the adsorption and reaction kinetics of potassium ions on electrode materials. This study delves into the specific effectiveness of defects in facilitating potassium storage, exploring the impact of defect-rich structures on dynamic processes. Employing ball milling, we introduce surface defects in EG, uncovering unique effects on its electrochemical behavior. These defects exhibit a remarkable ability to adsorb a significant quantity of potassium ions, facilitating the subsequent intercalation of potassium ions into the graphite structure. Consequently, this process leads to a higher potassium voltage. Furthermore, the generation of a diluted stage compound is more pronounced under high voltage conditions, promoting the progression of multiple stage reactions. Consequently, the EG sample post-ball milling demonstrates a notable capacity of 286.2 mAh g-1 at a current density of 25 mA g−1, showcasing an outstanding rate capability that surpasses that of pristine EG. This research not only highlights the efficacy of defect engineering in carbon materials but also provides unique insights into the specific manifestations of defects on dynamic processes, contributing to the advancement of potassium-ion battery technology. [ABSTRACT FROM AUTHOR]