Building better lithium-sulfur batteries: from LiNO3 to solid oxide catalyst

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Lithium nitrate (LiNO3) is a common additive in lithium-sulfur (Li-S) batteries.
• It is traditionally believed to improve rechargeability by forming a passivation layer on the lithium anode, suppressing polysulfide shuttles.
• Recent studies challenge this view, highlighting LiNO3's own reduction and limited polysulfide inhibition.

Purpose of the Study:

• To systematically investigate the true function of LiNO3 in Li-S batteries.
• To propose and validate a new mechanism for redox-shuttle suppression by LiNO3.
• To explore LiNO3-free strategies for enhanced Li-S battery performance.

Main Methods:

• Density functional theory (DFT) calculations.
• Electrochemical testing of Li-S cells with and without LiNO3.
• Analysis of self-discharge rates.
• Cathode modification with ruthenium oxide (RuO2).

Main Results:

• LiNO3 suppresses redox shuttles via catalyzed oxidation of polysulfides to sulfur by nitrate anions.
• This catalytic oxidation occurs on or near the electrode surface during charging.
• LiNO3-free cells with RuO2-modified cathodes show improved capacity and cycling stability (>400 cycles).

Conclusions:

• The primary role of LiNO3 is not anode passivation but catalytic oxidation of polysulfides.
• Nitrate anions act as catalysts for polysulfide oxidation, improving Li-S battery performance.
• Alternative strategies, like using oxygen evolution catalysts, can achieve similar benefits without LiNO3.