Feasibility of achieving two-electron K-O₂ batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Metal-oxygen batteries, particularly lithium-oxygen (Li-O2) and sodium-oxygen (Na-O2), suffer from poor reversibility and energy efficiency due to superoxide instability.
• Potassium-based systems (K-O2) offer a potential solution by stabilizing superoxide with larger potassium ions, enabling efficient, catalyst-free operation.

Purpose of the Study:

• To investigate redox mechanisms beyond the potassium superoxide (KO2) stage in K-O2 batteries.
• To explore the potential for enhanced capacity and efficiency by incorporating potassium peroxide (K2O2) redox.
• To determine optimal operating conditions, specifically cell design, for these advanced K-O2 battery chemistries.

Main Methods:

• Utilized solid potassium superoxide (KO2) dissolved in a dimethyl sulfoxide (DMSO)-based electrolyte.
• Performed three-electrode cyclic voltammetry scans under an argon atmosphere.
• Analyzed the electrochemical behavior to identify reversible redox reactions.

Main Results:

• Observed two distinct sets of reversible peaks during cyclic voltammetry, indicating multiple redox states.
• Identified a reversible KO2/potassium peroxide (K2O2) interconversion with a low overpotential (239 mV) and excellent reversibility, even without electrocatalysts.
• Discovered that K2O2 reacts with gaseous oxygen, impacting reversibility in open systems.

Conclusions:

• The KO2/K2O2 redox couple offers a promising pathway for high-performance K-O2 batteries, demonstrating superb reversibility and low overpotential.
• A closed cell system is essential for realizing the full potential of the reversible KO2/K2O2 redox, preventing unwanted reactions with gaseous oxygen.
• Future K-O2 battery development should focus on closed systems and explore strategies to leverage the K2O2 redox for increased capacity.