Triggered reversible phase transformation between layered and spinel structure in manganese-based layered compounds

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Layered cathode materials often undergo irreversible phase transformations to spinel structures, limiting their electrochemical performance.
• This phase transformation is typically considered detrimental, leading to capacity fading and structural degradation in batteries.

Purpose of the Study:

• To investigate the possibility of achieving reversible phase transformation in layered sodium birnessite (Na$_{x}$MnO$_{2}$·yH$_{2}$O).
• To elucidate the mechanism behind this reversible phase transformation and its impact on electrochemical properties.

Main Methods:

• Combined soft and hard X-ray absorption spectroscopy (XAS) with X-ray diffraction (XRD).
• First-principle calculations and kinetics investigations.
• Electrochemical reaction studies modulated by crystal water content.

Main Results:

• Demonstrated reversible transformation between layered and metastable spinel-like phases in Na$_{x}$MnO$_{2}$·yH$_{2}$O.
• Identified crystal water as a key factor enabling this reversibility.
• Observed activation of new cation sites, enhanced ion diffusion, and improved structural stability due to reversible phase changes.

Conclusions:

• The reversible phase transformation in sodium birnessite offers a new pathway for designing advanced cathode materials.
• Understanding and controlling framework reversibility is crucial for developing next-generation rechargeable batteries with improved longevity and performance.