High-Crystallinity MnO ₂ with Enhanced Structural Integrity for Aqueous Zn ²⁺ Storage

Manganese dioxide (MnO₂) is a promising cathode material for aqueous zinc ion batteries (AZIBs) due to its high theoretical capacity and natural abundance. However, its practical application is hindered by severe structural degradation caused by Jahn-Teller distortion and dissolution in aqueous environments. Herein, we report high-crystallinity layered MnO₂ synthesized via high-temperature calcination at 800 °C, in contrast to conventional low-temperature hydrothermal methods. The calcinated MnO₂ (MnO₂-cal) exhibits ordered lamellar morphologies with robust crystallinity and enhanced structural integrity, enabling a superior cycling stability even without Mn²⁺ electrolyte additives. Electrochemical tests reveal a reversible capacity of ∼135 mAh g^-1 with negligible capacity fading. Detailed ex situ XRD and XAS characterizations confirm the highly reversible structural evolution and stable Mn-O coordination during electrochemical operations. This work sheds light on the structural design and synthesis routes of manganese oxides, offering a novel viewpoint on developing long-life AZIB cathodes beyond traditional hydrothermal synthesis.