Promoting solution phase discharge in Li-O2 batteries containing weakly solvating electrolyte solutions.

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Lithium-oxygen (Li-O2) batteries face challenges with lithium peroxide (Li2O2) formation on the cathode surface during discharge.
• This surface deposition leads to low capacity, poor rate capability, and early cell failure.
• Achieving solution-phase Li2O2 formation is crucial for improving battery performance.

Purpose of the Study:

• To investigate the use of 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) as an additive to promote solution-phase Li2O2 formation in Li-O2 batteries.
• To understand the mechanism by which DBBQ influences Li2O2 deposition and battery performance.
• To enhance the capacity, rate, and cycle life of Li-O2 batteries.

Main Methods:

• Electrochemical testing of Li-O2 cells with and without DBBQ additive.
• Analysis of Li2O2 morphology and deposition pathways using various techniques.
• Investigation of electrolyte stability and additive interactions.

Main Results:

• DBBQ additive successfully promotes solution-phase Li2O2 formation even in low-polarity electrolytes.
• The additive suppresses detrimental Li2O2 film growth on the cathode surface.
• Significant improvements observed: 80- to 100-fold capacity increase, halved discharge overpotential, and high rate capability (>1 mA cm⁻²) achieved.
• DBBQ operates via a novel mechanism that bypasses the reactive LiO2 intermediate.

Conclusions:

• DBBQ is an effective additive for enhancing Li-O2 battery performance by controlling Li2O2 discharge product morphology.
• The additive enables high-capacity, high-rate operation and improves cycle life.
• This work opens new avenues for designing advanced electrolytes for Li-O2 batteries.