Sluggish Li₂O₂ dissolution - a key to unlock high-capacity lithium-oxygen batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Lithium-oxygen batteries offer high theoretical energy density but suffer from low practical discharge capacity.
• This limitation is primarily due to the passivation of the solid discharge product, lithium peroxide (Li₂O₂), on the electrode surface.
• Understanding Li₂O₂ deposition and dissolution is crucial for improving battery performance.

Purpose of the Study:

• To investigate and quantify the deposition and dissolution kinetics of Li₂O₂ in lithium-oxygen batteries.
• To identify factors influencing Li₂O₂ dissolution pathways and rates.
• To develop strategies for enhancing Li₂O₂ dissolution and increasing battery discharge capacity.

Main Methods:

• Electrochemical quartz crystal microbalance (EQCM) was employed to study Li₂O₂ deposition and dissolution.
• Electrode orientation effects on Li₂O₂ formation and deposition were analyzed.
• Two distinct Li₂O₂ dissolution modes (surface dissolution and bulk fragmentation) were identified and characterized.

Main Results:

• Electrode orientation significantly impacts Li₂O₂ formation path and deposition.
• Bulk fragmentation of Li₂O₂ was found to be 100 times faster than surface dissolution.
• An intermittent-desorption discharge strategy, utilizing a 2.9 V desorption potential, enabled 80% Li₂O₂ dissolution within 3 minutes, increasing discharge capacity by an order of magnitude.

Conclusions:

• Addressing Li₂O₂ dissolution challenges is key to achieving high practical specific energy in lithium-oxygen batteries.
• The identified dissolution kinetics and developed intermittent-desorption strategy offer a promising pathway for next-generation high-energy batteries.
• Further research into optimizing electrode-Li₂O₂ interactions can unlock the full potential of Li-O₂ battery technology.