Capacitive-Controlled Prussian White with a Nickel Iron Hexacyanoferrate Composite Cathode for Rapid Sodium Diffusion

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Prussian blue analogues are promising cathode materials for sodium-ion batteries (SIBs) due to their structure and cost-effectiveness.
• Sluggish ion diffusion limits practical specific capacity, especially at high current rates.

Purpose of the Study:

• To enhance the electrochemical performance of Prussian blue analogues for SIBs.
• To investigate the impact of Ni substitution and water coordination on Fe species for improved sodium storage.

Main Methods:

• Ni substitution in Prussian blue analogues.
• Formation of water-coordinated Fe species.
• Electrochemical testing at various current densities (0.5 C to 50 C).
• Potentiastatic tests, operando 57Fe Mössbauer spectroscopy, and ex situ XRD for mechanism elucidation.

Main Results:

• PW-325@2NiFe-55 delivered 95 mAh g-1 at 50 C with 72.5% capacity retention from 0.5 C.
• Maintained 80.2% capacity after 500 cycles at 5 C.
• Verified a dual mechanism involving diffusion-controlled and capacitive contributions for high-spin Fe, and a capacitive mechanism for low-spin Fe.

Conclusions:

• Ni substitution and water coordination effectively enhance sodium storage capacity and rate performance in Prussian blue analogues.
• The study elucidates the charge storage mechanisms, offering insights for designing high-performance SIB cathode materials.