High‐Performance MnO ₂ Hydrogel Composite Electrodes Constructed via In Situ Hofmeister Effect for Zinc–Ion Batteries

Abstract Manganese dioxide (MnO ₂ ) stands out as an ideal cathode material for aqueous zinc–ion batteries (AZIBs) owing to its high theoretical capacity (308 g ⁻¹ ) and environmental sustainability. However, conventional MnO ₂ electrode designs adapted from non‐aqueous batteries face persistent challenges in electrolyte permeability and structural stability, severely limiting the rate performance and cycling durability of Zn‐MnO ₂ batteries. Here, this study presents an innovative electrode design strategy utilizing water‐soluble biopolymers as hydrogel network, enhanced by the Hofmeister effect of SO ₄ ²⁻ ions naturally present in the electrolyte. The hydrogel network facilitates rapid Zn ²⁺ diffusion while providing mechanical flexibility to accommodate volume changes during charge–discharge cycles. As a result, the hydrogel composite electrode achieves exceptional rate capability, delivering over 245 mAh g ⁻¹ at 5 C and maintaining 160 mAh g ⁻¹ at 35 C, alongside outstanding cycling stability (146.9 mAh g ⁻¹ after 5000 cycles at 20 C). This work introduces a novel electrode design strategy for aqueous batteries and advances the development of high‐performance AZIBs for practical applications.