High Efficiency Alkaline Iodine Batteries with Multi-Electron Transfer Enabled by Bi/Bi₂O₃ Redox Mediator

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• The iodine/iodate (I-/IO3-) redox couple is promising for high-energy aqueous batteries.
• Alkaline electrolytes improve IO3- formation kinetics and Zn anode compatibility.
• Sluggish IO3- reduction kinetics limit energy efficiency in both acidic and alkaline conditions.

Purpose of the Study:

• To establish the redox mechanism of the I-/IO3- couple in alkaline electrolytes.
• To introduce a redox mediator (RM) to catalyze IO3- reduction.
• To enhance the performance of aqueous batteries utilizing the I-/IO3- redox couple.

Main Methods:

• Investigated the I-/IO3- redox mechanism in alkaline electrolytes.
• Employed Bi/Bi2O3 as a redox mediator (RM) for IO3- reduction.
• Assembled and tested a full battery with a Zn anode and Bi/Bi2O3 RM cathode.

Main Results:

• Established the fundamental redox mechanism of I-/IO3- in alkaline media.
• Bi/Bi2O3 RM reduced the charge/discharge voltage gap from 1.6 V to 1 V.
• Achieved high areal capacity (12 mAh/cm2) and stable cycling (>400 cycles) at 5 mAh/cm2.

Conclusions:

• Bi/Bi2O3 effectively catalyzes IO3- reduction, overcoming kinetic limitations.
• The developed Zn//I-/IO3- battery demonstrates significant improvements in energy efficiency and cycle life.
• This work paves the way for high-performance alkaline aqueous batteries.