Resolving the Kinetics-Stability Trade-Off in Prussian Blue Analogues for Aqueous Ca-Ion Batteries: A High-Entropy...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Prussian blue analogues (PBAs) are promising cathode materials for aqueous calcium-ion batteries (CIBs).
• A key challenge is the trade-off between kinetics and stability due to intrinsic vacancies.
• Vacancies enhance ion kinetics but destabilize the crystal framework, leading to material degradation.

Purpose of the Study:

• To address the kinetics-stability conflict in PBAs for CIBs.
• To develop a novel high-entropy PBA (HEPBA) cathode material.
• To improve the performance and longevity of aqueous CIBs.

Main Methods:

• Deliberately induced vacancies at Fe(CN)6 sites.
• Engineered a high-entropy configuration at transition metal (TM) sites.
• Investigated d-d orbital coupling and delocalized electronic networks for charge compensation.

Main Results:

• The high-entropy environment promoted d-d orbital coupling, creating a delocalized electronic network.
• This network suppressed vacancy migration and aggregation, mitigating TM dissolution via a "vacancy caging" mechanism.
• The HEPBA cathode achieved a record reversible capacity of 112 mAh g-1 at 50 mA g-1 and 88.24% retention over 24,000 cycles at 2000 mA g-1.

Conclusions:

• The "vacancy caging" strategy effectively balances kinetics and stability in PBAs.
• High-entropy engineering offers a viable pathway to overcome limitations in vacancy-rich cathode materials.
• This work paves the way for advanced high-performance aqueous calcium-ion batteries.