High-Entropy Metal-Organic Frameworks for Highly Reversible Sodium Storage

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Prussian blue analogues (PBAs) are promising sodium storage materials due to their metal-organic framework structure.
• However, PBAs suffer from low specific capacity and poor reversibility caused by phase transitions during cycling.
• These limitations hinder their practical application in sodium-ion batteries.

Purpose of the Study:

• To enhance the electrochemical properties of PBAs for sodium storage.
• To overcome the limitations of low capacity and poor reversibility in traditional PBAs.
• To investigate the effect of high entropy on PBA performance.

Main Methods:

• Introduction of five different metal species into the PBA crystal structure to create high-entropy PBAs (HE-PBAs).
• Tuning the configurational entropy beyond 1.5R through multi-element substitution.
• Characterization of HE-PBAs using electrochemical cycling and analysis of gassing behavior.

Main Results:

• HE-PBAs exhibit a quasi-zero-strain reaction mechanism, leading to improved cycling stability.
• Enhanced rate capability was observed in the HE-PBA materials.
• Detection of cyanogen evolution indicates structural degradation, but optimized electrochemical windows yield nearly 100% Coulombic efficiency after 3000 cycles.

Conclusions:

• High entropy introduction significantly improves the electrochemical performance of PBAs for sodium storage.
• HE-PBAs offer a promising strategy to overcome the intrinsic limitations of traditional PBAs.
• Further optimization of operating conditions can lead to long-term stable sodium-ion battery performance.