Efficient Regulation of Oxygen Vacancies in β-MnO2 Nanostructures for High-Loading Zinc-Ion Batteries

Manganese-based oxides, particularly β-MnO2, have emerged as promising cathode materials for aqueous zinc-ion batteries (ZIBs) due to their high theoretical capacity, low cost, and intrinsic safety. However, their sluggish reaction kinetics, limited active sites, and poor conductivity often lead to suboptimal electrochemical performance. To address these limitations, we propose a facile ethanol-mediated hydrothermal strategy to engineer rod-like β-MnO2 nanostructures with tailored oxygen vacancies. By precisely adjusting ethanol addition (3–5 mL) during synthesis, oxygen vacancy concentrations were optimized to enhance electronic conductivity and active site exposure. The experimental results demonstrate that β-MnOx-2-5 synthesized with 5 mL of ethanol delivers an exceptional areal capacity of 4.87 mAh cm−2 (348 mAh g−1, 469.8 Wh kg−1) at 200 mA cm−2 under a high mass loading of 14 mg cm−2. Further, a hybrid electrode combining oxygen-deficient β-MnO2-x-3 (air-calcined) and structurally stable β-Mn5O8-y-3 (Ar-calcined) achieves a retained capacity of 3.9 mAh cm−2 with stable cycling performance, achieving an optimal equilibrium between high capacity and long-term operational durability. Systematic characterizations (XPS, ESR, XANES, FT-EXAFS) confirm vacancy-induced electronic structure modulation, accelerating ion diffusion and redox kinetics. This scalable vacancy engineering approach, requiring only ethanol dosage control, presents a viable pathway toward industrial-scale ZIB applications.