Understanding the Structural Evolution and Lattice Water Movement for Rhombohedral Nickel Hexacyanoferrate upon...

Area of Science:

• Materials Science
• Electrochemistry
• Inorganic Chemistry

Background:

• Prussian blue analogues (PBAs) are promising cathode materials for sodium-ion batteries due to their adaptable structures.
• Developing high-performance and stable PBAs is crucial for advancing sodium-ion battery technology.

Purpose of the Study:

• To synthesize a high-performance rhombohedral nickel hexacyanoferrate cathode material.
• To investigate the structural evolution and sodium-ion migration mechanisms in PBAs during electrochemical cycling.

Main Methods:

• Controllable low-temperature synthesis of rhombohedral nickel hexacyanoferrate.
• Electrochemical performance testing, including long-term cycling and rate capability.
• Ex situ X-ray absorption spectroscopy (XAS) and in situ X-ray diffraction (XRD) for structural analysis.
• Fourier transform infrared (FTIR) spectroscopy to study lattice water movement.

Main Results:

• The synthesized PBA delivered 87.8% capacity retention after 10,000 cycles at 10C and a discharge capacity of 53 mAh g⁻¹ at 40C.
• Superior electrochemical performance is linked to minimal lattice alteration and reversible rhombohedral-cubic phase transitions.
• FTIR analysis validated a nonlinear Na+ migration path and identified lattice distortion caused by Na(OH2)+ units.

Conclusions:

• The study presents a high-performance PBA cathode material for sodium-ion batteries.
• Understanding the structural dynamics and ion migration pathways provides insights for designing improved PBA materials.
• The findings offer a modified mechanism for PBA performance, guiding future material development.