Exclusive Solution Discharge in Li-O₂ Batteries?

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aprotic lithium-oxygen (Li-O₂) batteries are promising for high energy density.
• Reversible lithium peroxide (Li₂O₂) electrodeposition is crucial for battery performance.
• Current models debate Li₂O₂ growth mechanisms: surface-adsorbed vs. solvated species.

Purpose of the Study:

• To investigate the dominant Li₂O₂ formation mechanism in Li-O₂ batteries.
• To challenge the prevailing understanding of Li₂O₂ growth.
• To establish a unified mechanism explaining Li₂O₂ morphology and capacity limitations.

Main Methods:

• Experimental investigation across diverse electrolytes, carbon materials, and current densities.
• Analysis of Li₂O₂ morphology and electrochemical performance.
• Development of a unified oxygen reduction mechanism.

Main Results:

• Li₂O₂ predominantly forms as particles via solution-mediated disproportionation of LiO₂, irrespective of electrolyte or current density.
• The proposed unified mechanism explains observed capacity relations and Li₂O₂ morphologies.
• Capacity is limited by mass transport through tortuous Li₂O₂, not electron transport through a passivating film.
• High capacities can be achieved with weakly solvating electrolytes under specific conditions.

Conclusions:

• The prevalence of surface growth for Li₂O₂ under practical conditions is questionable.
• Species mobilities, areal rate, and LiO₂ association dictate particle morphology and capacity.
• Understanding solution-mediated Li₂O₂ formation is key to advancing Li-O₂ battery technology.