Korea University: Professor Yu Seung-ho’s Group Developed a ‘Next-Generation Sodium-Ion Battery Cathode Material’

Professor Yu Seung-ho’s group in the Department of Chemical and Biological Engineering at KU (first author: Yoon Geon-hee in the first year of the master’s course at KU) conducted a joint study with Professor Kim Du-ho’s group in the Department of Mechanical Engineering at Kyung Hee University (first author: Koo So-jung in the second year of the master’s course at KU) on sodium-ion battery cathode materials. The aim was to present a method of overcoming the limitation of oxygen (anion) redox, which is currently a sticking point in battery development, and to investigate the causes of the problem. The results of their study provided new directions for the design of sodium-ion battery cathode materials considering oxygen redox.
The authors suggested the possibility of resolving the degradation caused by oxygen redox, which has been a sticking point for the development of sodium-ion secondary batteries, and the results of their study were published in Advanced Energy Materials (IF=29.368), a globally acclaimed journal, on February 8.

Sodium-ion secondary battery technology is a renewable energy technology that can resolve the economic feasibility issues of commercially available lithium-ion secondary batteries. Sodium-ion secondary batteries have been drawing much attention due to the abundant reserves of sodium and the relatively economical prices of the component materials. However, the technology has limitations, such as low capacity and low energy density compared to lithium-ion batteries. Many studies have been conducted on the oxygen (anion) redox of the cathode materials, as a strategy to overcome these limitations.

Sodium-ion battery cathode material has a layered structure in which sodium, a transition metal, and oxygen are combined. Generally, the transition metal plays a central role in redox during the battery charge/discharge process, and this redox is referred to as cationic redox. As the redox is enhanced, the energy density of secondary batteries increases. Recent studies have shown that not only transition metals but also oxygen can participate in the redox, and this oxygen redox is referred to as anionic redox. When this reaction is also utilized, the total quantity of redox can be increased to provide a much higher electrode capacity and higher cell energy density. However, the low reversibility of this anionic redox poses additional problems, including reduced battery lifetimes and decreased ion diffusion rates, that require solutions.

Professor Yu doped a small amount of external ions to the transition metal layer of the sodium-ion secondary battery cathode material to increase the reversibility of the oxygen redox. The principles of the oxygen redox were better understood by verifying the process through the electrochemical analyses, experiments with various materials, and density functional theory (DFT)-based calculations carried out by Professor Kim’s group. The new cathode material, synthesized without a significant structural change, not only improved the reversibility of the oxygen redox in the discharge process following a charge process but also demonstrated high structural reversibility as well as improved rate performance. The calculations carried out in this study showed that the internal doping of the aluminum ions formed an additional thermodynamically stable phase, stabilized the lattice oxygen, and enhanced the participation of oxygen in the redox.

Professor Yu said, “We expect that the aluminum ion doping strategy presented in our study will increase the voltage, capacity and stability of the cathodes of sodium-ion secondary batteries, making significant contributions to their commercialization.”

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