South Korean researchers have recently discovered that the performance of lithium-air batteries has a greater correlation with the content of carbon dioxide. Researchers believe that the Li2CO3 in the battery can be selectively used as the final product of the discharge reaction according to the dielectric properties of the electrolyte in the lithium-air battery. In addition, they also verified that Li2CO3 can undergo a reversible reaction in the lithium-oxygen/carbon dioxide battery cycle. Related papers have been published in the "Journal of the American Chemical Society". Researchers believe that understanding the chemical properties of CO2 in lithium-air batteries and the use of carbon dioxide when the electrolyte is dissolved is of great significance to the development of lithium-air batteries. In addition, exploring the possibility of rechargeable lithium-oxygen/carbon dioxide batteries based on Li2CO3 has one of the greatest advantages to minimize adverse reactions.

The highest theoretical energy density of lithium-air batteries is about 3,500 Wh/kg, which is a good power source for the next generation of electric vehicle energy storage systems, enabling electric vehicles to achieve longer formal mileage. The structure of the lithium-air battery is based on a pair of intercalation electrodes. When charging, lithium ions move from the cathode to the electrolyte and then the anode; when discharging, the process is reversed.

Li-air batteries are still facing many technical and engineering problems in order to achieve commercialization, including insufficient understanding of battery reaction mechanisms, unstable electrolyte chemical properties, short cycle life, and low ion transfer rate. To a large extent led to the phenomenon of excessive battery load.

The researchers pointed out: It is not yet known what happens when lithium-air batteries are tested in an oxygen-free environment, because most previous studies have been tested in an oxygen-free environment, and other components in the air are related to battery performance. The impact is negligible. Therefore, to prove the impact of carbon dioxide on lithium-air batteries, it is necessary to create a greenhouse environment and study the effects of other components in the air (nitrogen, argon, water, carbon dioxide) on battery performance one by one.

Assuming that water (an important substance that leads to the deterioration of electrolytes and anodes) can be removed through the 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. The cathode voltage of a traditional lithium-air battery is 3 volts. When the surrounding environment contains argon and nitrogen, the voltage of 3 volts cannot activate the electrochemical reaction, while carbon dioxide can withstand the electrochemical reaction due to its inertness.

The difference in chemical stability means that the final product Li2O2 will always be converted into Li2CO3 through carbon dioxide, and this irreversible reaction limits the cycle performance of lithium-air batteries.

In addition, although the proportion of carbon dioxide in the air is not high, because carbon dioxide has a high solubility (50 times higher than oxygen), it is used in battery reactions. In order to further develop lithium-air battery technology, the impact of carbon dioxide and Li2CO3 on the performance of lithium-air batteries must be taken into consideration.

The Korea Advanced Institute of Science and Technology (Korea Advanced Institute of Science and Technology) and the Seoul National University (Seoul National University) research team have studied the reaction mechanism of lithium oxygen/carbon dioxide batteries using a combination of quantum mechanics simulation and experimental verification under various electrolyte conditions.

They found that a low-dielectric electrolyte would form Li2O2, while a high-dielectric electrolyte would activate carbon dioxide and produce Li2CO3. However, the unexpected gain is that they found that high dielectric materials such as dimethyl inkstone (DMSO) can cause a reversible reaction of Li2CO3.

The researchers said that this discovery is very important, because in an environment containing carbon dioxide, the formation of Li2CO3 in lithium-air batteries is unavoidable. However, substances that can promote reversible reactions have been found to improve the cycle performance of the battery. Stablize.

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