Researchers believe that Li₂CO₃ in the battery can selectively serve as the final product of the discharge reaction, depending on the dielectric properties of the electrolyte in lithium-air batteries. Furthermore, they have verified that Li₂CO₃ can undergo reversible reactions during lithium-oxygen/carbon dioxide battery cycling. The related paper has been published in the *Journal of the American Chemical Society*. The researchers believe that understanding the chemical properties of CO₂ in lithium-air batteries and the role of carbon dioxide in electrolyte dissolution is crucial for the development of lithium-air batteries. Additionally, exploring the possibility of rechargeable lithium-oxygen/carbon dioxide batteries based on Li₂CO₃ has the significant advantage of minimizing adverse reactions.
The highest theoretical energy density of lithium-air batteries is approximately 3500 Wh/kg, making them a promising power source for next-generation electric vehicle energy storage systems, potentially enabling longer driving ranges. The structure of a lithium-air battery is based on a pair of intercalation electrodes. During charging, lithium ions move from the cathode to the electrolyte and then to the anode; during discharging, this process is reversed.
Lithium-air batteries still face many technological and engineering challenges before reaching the commercialization stage, including insufficient understanding of battery reaction mechanisms, unstable chemical properties of electrolytes, short cycle life, and low ion transfer rates, all of which contribute significantly to the phenomenon of excessive battery load.
Researchers point out that it is currently unclear what happens when lithium-air batteries are tested in an oxygen-free environment, as most previous studies have been conducted in oxygen-rich environments, neglecting the influence of other air components on battery performance. Therefore, to demonstrate the impact of carbon dioxide on lithium-air batteries, a greenhouse environment must be created, and the effects of other air components (nitrogen, argon, water, and carbon dioxide) on battery performance must be studied individually.
Assuming that moisture (a key substance leading to electrolyte and anode degradation) can be removed through a waterproof membrane, carbon dioxide should have the most significant impact on the chemical properties of lithium-air batteries, exceeding the influence of other components in the air. Traditional lithium-air batteries have a cathode voltage of 3 volts. In the presence of argon and nitrogen in the surrounding environment, a voltage of 3 volts cannot activate the electrochemical reaction, while carbon dioxide, due to its high inertness, can withstand the corresponding electrochemical reaction.
The difference in chemical stability means that the final product Li2O2 will always be converted into Li2CO3 through carbon dioxide. This irreversible reaction limits the cycle performance of lithium-air batteries.
Furthermore, although carbon dioxide constitutes a small proportion of the air, its high solubility (50 times higher than oxygen) makes it suitable for use in battery reactions. To further develop lithium-air battery technology, the impact of carbon dioxide and Li₂CO₃ on lithium-air battery performance must be taken into account.
A research team from the Korea Advanced Institute of Science and Technology and Seoul National University studied the reaction mechanism of lithium-oxygen/carbon dioxide batteries under various electrolyte conditions by combining quantum mechanical simulations with experimental verification.
They discovered that a low-dielectric electrolyte forms Li₂O₂, while a high-dielectric electrolyte activates carbon dioxide to form Li₂CO₃. However, an unexpected finding was that high-dielectric media such as dimethyl dioxide (DMSO) can cause a reversible reaction in Li₂CO₃.
Researchers say this discovery is very important because the formation of Li2CO3 in lithium-air batteries is unavoidable in carbon dioxide-containing environments. However, a substance has now been discovered that can promote a reversible reaction, making the battery's cycle performance more stable.
