β-MnOOH Converted δ-MnO₂ with New Layer-to-Layer Charge Storage as Cathode for Zinc-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Layer-structured birnessite δ-MnO₂ is a potential cathode material for aqueous zinc-ion batteries (ZIBs).
• Current δ-MnO₂ cathodes often form non-layered structures during discharge, limiting reversible charge storage.
• Conventional layered materials typically rely on intercalation electrochemistry for charge storage.

Purpose of the Study:

• To investigate feitknechtite β-MnOOH and its isostructural anodized δ-MnO₂ as cathode materials for ZIBs.
• To explore the charge storage mechanism and performance enhancements of anodized δ-MnO₂ in aqueous electrolytes.
• To uncover new phase transformations in Mn-based cathodes for improved ZIBs.

Main Methods:

• Synthesis of feitknechtite β-MnOOH and isostructural anodized δ-MnO₂ via an anodization method.
• Application of these materials as cathodes in aqueous ZIBs with Zn metal anodes.
• Experimental characterization combined with theoretical simulations to elucidate charge storage mechanisms.

Main Results:

• Anodized δ-MnO₂, with larger interlayer spacing than β-MnOOH, exhibited improved charge transfer kinetics and Mn redox reversibility.
• Significant enhancements in cyclicity and rate capability were observed for anodized δ-MnO₂ cathodes.
• A novel layer-to-layer charge storage mechanism was revealed, involving the reversible transformation between anodized δ-MnO₂ and β-MnOOH.

Conclusions:

• The minor presence of β-MnOOH in anodized δ-MnO₂ facilitates a unique phase transformation for charge storage.
• Anodized δ-MnO₂ demonstrates superior performance in aqueous ZIBs compared to β-MnOOH.
• This study opens new avenues for developing efficient layered cathode materials for ZIBs.