Studies on improving peroxodicarbonate intermediate stability in carbon dioxide-assisted lithium-oxygen batteries

Abstract

With the rapid development of the electric vehicle market, there is a growing demand for electric vehicles that can achieve driving ranges surpassing those of internal combustion engine vehicles. In order to fulfill this requirement, the development of energy storage systems with higher energy density than current lithium-ion batteries are crucial. Lithium-air batteries, promising as the next-generation batteries, offer theoretical energy densities that are more than 3 to 5 times higher than those of lithium-ion batteries. Previous research has primarily focused on the oxygen electrochemistry in lithium-air batteries, the active material of which is oxygen. However, the instability of lithium superoxide (LiO2) radicals generated during the oxygen reduction reaction and the low electrical conductivity of discharge products such as lithium peroxide (Li2O2) and lithium carbonate (Li2CO3) have hindered their practical application due to high overpotentials and low cyclability. This doctoral thesis investigates novel electrochemical and chemical reactions occurring in lithium-oxygen batteries by introducing a small amount of carbon dioxide, simulating an atmospheric-like environment. Furthermore, it demonstrates that lithium-oxygen batteries containing carbon dioxide can improve their cyclability through temperature and electrolyte modulation. In Chapter 2, the electrochemical analysis based on the concentration of carbon dioxide (CO2) and the Li+ solvation ability in the electrolyte is explained. Chapter 3 focuses on understanding the reaction pathways and mechanisms of electrochemical and chemical reactions in lithium-oxygen batteries containing carbon dioxide under different temperatures and electrolytes. In particular, by enhancing the stability of peroxodicarbonate (C2O62-) intermediates, it successfully suppresses the precipitation caused by irreversible reactions of Li2CO3, dramatically improving the battery's cyclability up to approximately 100 cycles. Chapter 4 investigates the stability of the metallic lithium electrode in the presence of oxygen and carbon dioxide environments. It examines the corrosion of the metallic lithium electrode induced by dimethylacetamide, which is the solvent used in this study. It investigates the compositional changes at the electrode-electrolyte interface caused by oxygen and carbon dioxide, discussing the resulting electrode stability.