Chelation-Buffer Co-Additives Enable Compact Zn Deposition and High-Rate Cycling in Zn-Br₂ Hybrid Flow Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Zinc-bromine hybrid flow batteries offer safe, sustainable energy storage using earth-abundant materials.
• Current limitations include uneven zinc deposition, parasitic reactions, and efficiency loss at high rates.

Purpose of the Study:

• To develop a dual-additive anolyte to improve zinc electrodeposition and battery performance.
• To investigate the mechanisms behind improved stability and efficiency.

Main Methods:

• Utilized a dual-additive system combining a chelating ligand (EDTA) and a pH-buffering anion (acetate).
• Employed Zn K-edge X-ray absorption spectroscopy (XAS) and X-ray tomographic microscopy (XTM) to analyze zinc deposition.
• Conducted rate tests up to 200 mA cm⁻² and long-term cycling at 35 mAh cm⁻².

Main Results:

• The dual-additive electrolyte stabilized zinc deposition, forming compact, continuous zinc networks.
• Achieved reduced overpotentials and high Coulombic efficiency (CE ≥ 95%) at high rates.
• Demonstrated superior capacity retention over ≥300 cycles compared to controls.

Conclusions:

• The chelation-buffer coadditive strategy effectively modulates Zn²⁺ solvation and interfacial acidity.
• Established a mechanistic link between coordination restructuring, 3D deposit connectivity, and improved cell performance.
• Provides a basis for designing advanced electrolytes for mildly acidic zinc-bromine systems.