An Advanced High-Performance Ultrafast Ammonium-Ion Aqueous Battery Based on Dual-Metal Redox Open Framework...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Ammonium-ion batteries (AIBs) are emerging as a sustainable alternative to lithium-ion batteries.
• Developing efficient and cost-effective cathode materials is crucial for AIB advancement.
• Metal-free battery chemistries are desirable for environmental and economic reasons.

Purpose of the Study:

• To investigate potassium manganese-iron hexacyanoferrate (KMnFeHCF) as a cathode for metal-free AIBs.
• To evaluate the electrochemical performance, structural properties, and ion transport mechanisms of KMnFeHCF.
• To assess the potential of KMnFeHCF as a sustainable energy storage material.

Main Methods:

• Synthesis and characterization of KMnFeHCF Prussian blue analog.
• Electrochemical testing including cyclic voltammetry, galvanostatic charge-discharge, and long-term cycling.
• Mössbauer spectroscopy and X-ray photoelectron spectroscopy for valence state analysis.
• Density functional theory (DFT) calculations for ion migration and structural analysis.
• Galvanostatic intermittent titration technique (GITT) for diffusion coefficient determination.

Main Results:

• KMnFeHCF exhibits a face-centered cubic structure with mixed-valence Fe⁺³/Fe⁺² states.
• The material delivers high specific capacities (~145 mAh/g at 3 A/g) and excellent coulombic efficiency (~97%).
• Reversible Fe²⁺/Fe³⁺ and Mn²⁺/Mn³⁺ redox transitions drive electrochemical performance.
• DFT calculations indicate favorable NH₄⁺ mobility with a low migration barrier (1.29 eV).
• A full cell demonstrates stable operation up to 1.8 V with remarkable cycling stability (50% capacity retention after 1850 cycles).

Conclusions:

• KMnFeHCF is a promising, cost-effective, and environmentally friendly cathode for metal-free AIBs.
• The open-framework structure facilitates efficient ammonium-ion diffusion and accommodates structural changes.
• This material offers a viable pathway towards sustainable and high-performance aqueous energy storage solutions.