Functionalized Phosphonium Cations Enable Zinc Metal Reversibility in Aqueous Electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous rechargeable zinc metal batteries offer safety and cost advantages.
• Achieving high zinc reversibility is critical for commercial viability.
• Existing electrolytes often struggle with dendrite formation and limited cycle life.

Purpose of the Study:

• To improve zinc reversibility in aqueous electrolytes.
• To develop a stable interphase layer for dendrite-free zinc plating/stripping.
• To demonstrate the performance of a novel electrolyte in full battery cells.

Main Methods:

• Utilized phosphonium-based cations with ether linkages in aqueous electrolytes.
• Investigated interfacial structures and chemistries using microscopic characterization.
• Performed electrochemical cycling tests at various current densities and Zn utilization.
• Assembled and tested full cells with a Na2V6O16·1.63H2O cathode.

Main Results:

• Achieved dendrite-free Zn plating/stripping for over 6400 hours at 0.5 mA/cm² and 280 hours at 2.5 mA/cm².
• Maintained a coulombic efficiency above 99% even with 20% Zn utilization per cycle.
• Demonstrated excellent full cell cycling performance with 2000 cycles at 300 mA/g.
• Identified unique interphase chemistry from phosphonium as key to reversible Zn cycling.

Conclusions:

• Phosphonium-based cations, particularly with ether linkages, significantly enhance Zn reversibility in aqueous electrolytes.
• The developed electrolyte enables stable and efficient zinc metal battery operation, overcoming previous limitations.
• This work paves the way for practical and high-performance aqueous rechargeable zinc metal batteries.