Rechargeable multivalent ion battery such as Mg-ion battery is considered as a candidate for high-density battery technology because of its high volumetric capacity and low tendency to form dendrites. Development of cathode materials for Mg-ion batteries requires good understanding of the intercalation and adsorption processes of Mg²⁺ ions into and on the host materials. We observed recently that nanostructure is beneficial for the development of Mg²⁺ cathode materials with high capacity. In this work, we describe the preparation of flower-like three-dimensional (3D) nanostructures of birnessite MnO₂ through an electrochemical conversion reaction from γ-MnS. This 3D birnessite MnO₂ exhibited a total capacity of ~360 mAh/g in aqueous electrolyte for the initial cycle. We further characterized the insertion of Mg²⁺ ions in the atomic layers of MnO₂ nanoflowers using scanning transmission electron microscopy (STEM) technique, revealing the energy storage mechanism of Mg²⁺ ions in 3D, ion-accessible MnO₂ nanostructures.

镁离子电池等可充电多价离子电池因其高体积容量和低形成枝晶的倾向而被认为是高密度电池技术的候选者。镁离子电池正极材料的开发需要充分了解 Mg ²⁺离子在主体材料中的嵌入和吸附过程。我们最近观察到纳米结构有利于开发高容量的Mg ^{2+正极材料。}在这项工作中，我们描述了通过 γ-MnS 的电化学转化反应制备水钠锰矿 MnO ₂的花状三维 (3D) 纳米结构。这种 3D 水钠锰矿 MnO ₂在初始循环中，在含水电解质中表现出约 360 mAh/g 的总容量。我们使用扫描透射电子显微镜 (STEM) 技术进一步表征了 Mg 2+ 离子在 MnO 2 纳米花的原子层中的插入^，_揭示了Mg ²⁺离子在 3D、离子可接近的 MnO ₂纳米结构中的能量存储机制。