Unraveling reaction discrepancy and electrolyte stabilizing effects of auto-oxygenated porphyrin catalysts in lithium–oxygen and lithium–air cells

Abstract

Lithium–oxygen (Li–O₂) batteries are an emerging energy storage alternative with the potential to meet the recent increase in demand for high-energy-density batteries. From a practical viewpoint, lithium–air (Li–Air) batteries using ambient air instead of pure oxygen could be the final goal. However, the slow oxygen reduction and evolution reactions interfere with reversible cell operation during cycling. Therefore, research continues to explore various catalyst materials. The present study attempts to improve the performance of Li–Air batteries by using porphyrin-based materials known to have catalytic effects in Li–O₂ batteries. The results confirm that the iron phthalocyanine (FePc) catalyst not only exhibits a catalytic effect in an air atmosphere with a low oxygen fraction but also suppresses electrolyte decomposition by stabilizing superoxide radical ions (O₂⁻) at a high voltage range. Density functional theory calculations are used to gain insight into the exact FePc-mediated catalytic mechanism in Li–Air batteries, and various ex situ and in situ analyses reveal the reversible reactions and structural changes in FePc during electrochemical reaction. This study provides a practical solution to ultimately realize an air-breathing battery using nature-friendly catalyst materials.