Session: Advances in Materials Synthesis & Characterization of Li-ion, Na-ion & Multi-Valent Batteries:

Rechargeable Mg-ion battery is considered as a possible candidate for post-lithium ion battery technology because of its high volumetric capacity, and low tendency to form dendrites. Development of cathode materials for Mg-ion batteries is hindered in part by a lack of understanding of the intercalation of Mg²⁺ ions into host materials. Birnessite MnO₂ is of interest for its unique layered structure with edge-sharing MnO₆ units. It has been studied as a promising material for supercapacitor and explored as a cathode material for multivalent batteries. However, the ion intercalation mechanism of birnessite MnO₂ remains unclear. Recently, we reported that reducing the size of cathode particles could greatly increase the charge capacity of Mg²⁺ intercalation hosts. This size-dependent enhancement in capacity suggests that a new strategy for making active electrode materials can be realized by creating nanoparticles with three dimensional (3D) structures. In my poster, I’ll present microscopic and spectroscopic evidence of Mg²⁺ insertion into flower-like nanostructured birnessite MnO₂ cathodes. The birnessite-phase MnO₂ cathode was made through in-situ electrochemical conversion of a spherical γ-MnS precursor. This birnessite MnO₂ shows a capacity of ~360 mAh/g in aqueous electrolyte, attributed to its layered nanostructures that facilitate the diffusion of Mg²⁺ ions. Using STEM with a high angle annual dark-field (HAADF) detector, we for the first time directly observed the intercalated Mg²⁺ ions in the layered structures of birnessite MnO₂ nanoflower, confirming that Mg²⁺ intercalation took place during the charge/discharge process. The observation of Mg²⁺ in layers of MnO₂ helps understand the intercalation mechanism in multivalent ion batteries.

Wenxiang Cjem

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