<p>Aqueous zinc-ion batteries (AZIBs) have attracted significant attention for large-scale energy storage due to their high safety and cost-effectiveness. Vanadium oxide (V₂O₅) is a promising cathode material but suffers from poor electrical conductivity and structural instability. In this study, we move beyond qualitative observations by systematically investigating the influence of ball milling time (2–5&#xa0;h) on V₂O₅ to establish direct quantitative correlations between processing duration, particle size reduction, relative oxygen vacancy concentration, and electrochemical performance. Ball milling reduces the average particle size from 375 to 278&#xa0;nm and increases the relative oxygen vacancy concentration by 28% (quantified by EPR signal intensity) without altering the crystal structure. Systematic evaluation across four milling durations reveals progressive capacity improvements: 85.3 mAh g⁻¹ (2&#xa0;h) → 161.3 mAh g⁻¹ (3&#xa0;h) → 178.6 mAh g⁻¹ (4&#xa0;h) → 199.1 mAh g⁻¹ (5&#xa0;h) at 1 A g⁻¹, with the optimized 5&#xa0;h sample achieving excellent cycling stability of 96.4% capacity retention after 100 cycles. This synergistic optimization through dual-scale refinement—reducing both agglomerate size (SEM) and crystallite size (XRD: 38.6 → 23.4&#xa0;nm)—coupled with oxygen vacancy engineering, shortens diffusion paths and increases active site density. This work establishes quantitative structure–property correlations connecting milling duration, defect concentration, and electrochemical behavior—going beyond previous qualitative observations of mechanically induced defects—and provides practical guidelines for scalable optimization of vanadium oxide cathodes.</p>