High-Performance MnO2 Hydrogel Composite Electrodes Constructed via In Situ Hofmeister Effect for Zinc–Ion Batteries

Manganese dioxide (MnO₂) 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 MnO₂ 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-MnO₂ batteries. Here, this study presents an innovative electrode design strategy utilizing water-soluble biopolymers as hydrogel network, enhanced by the Hofmeister effect of SO₄²⁻ ions naturally present in the electrolyte. The hydrogel network facilitates rapid Zn²⁺ 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.