Guest water hinders sodium-ion diffusion in low-defect Berlin green cathode material

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Prussian blue analogues (PBAs) like NaFe[Fe(CN)6]·nH2O are promising cathode materials for sodium-ion batteries.
• Concerns exist regarding their long-term electrochemical performance and rate capability due to structural factors.
• Controlling [Fe(CN)6] vacancies and water content is key to improving PBA performance.

Purpose of the Study:

• To investigate the impact of varied water content on the electrochemical properties of low-defect Berlin green (BG).
• To optimize BG as a cathode material for enhanced sodium-ion battery performance.

Main Methods:

• Studied BG with water content ranging from 10 to 2 wt%.
• Electrodes were cycled within a narrow voltage window (3.15-3.8 V vs. Na/Na+) to maintain cubic structure.
• Systematically analyzed the effect of thermal dehydration on electrochemical properties.

Main Results:

• Thermal dehydration significantly improved cycling stability, exceeding 300 cycles at 15 mA g-1 with >99.9% coulombic efficiency.
• The electrode with the lowest water content demonstrated faster Na+ ion insertion/extraction.
• CV peak currents were larger in dehydrated samples compared to hydrated ones.

Conclusions:

• Optimizing water content in BG is crucial for enhancing its electrochemical performance in sodium-ion batteries.
• Dehydrated PBAs offer improved cycling stability and rate capability.
• This research provides fundamental insights for designing advanced electrode materials for energy storage.