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Unveiling the intermolecular mechanisms behind OEM dissolution in organic batteries

A new study has revealed significant insights into the intermolecular mechanisms involved in the dissolution of organic electrode materials (OEMs) within electrolytes during battery cycling tests.

Jointly led by Professor Won-Jin Kwak from the Department of Mechanical Engineering at UNIST and Professor Joonmyung Choi from Hanyang University, this research demonstrates the strong cation-solvent interaction energy within the electrolyte induces the accelerated dissolution of OEMs. The work is in the journal ACS Nano.

Organic batteries represent the next-generation of secondary batteries, replacing traditional metal electrodes, such as lithium and nickel, with cost-effective organic materials that can be manufactured on a continuous basis in industrial settings.

However, the short lifespan of these batteries remains a significant barrier to commercialization, primarily due to the severe dissolution of OEMs into the electrolyte. While various studies have sought to address this issue, the underlying causes of dissolution have yet to be clearly identified.

The research indicates that strong cation-solvent interactions promote co-intercalation—a process whereby solvent molecules are incorporated along with cations into the microstructure of the electrode. When cations penetrate the electrode's internal structure, the involvement of solvent molecules causes it to expand, allowing the electrode material to flow out more readily. In contrast, weak interactions facilitate the straightforward insertion of cations without solvent involvement.

The research team arrived at these conclusions by systematically examining and analyzing experimental results with varying cation types, as well as calculating the interaction energy between cations and solvents. Their experiments, which involved lithium, sodium, and potassium ions, revealed that lithium ions produced the most pronounced interactions with solvent molecules, resulting in thinner electrodes with higher interaction energies.

Hyun-Wook Lee, the first author of the study, commented, "While previous research on organic electrodes primarily focused on restructuring materials to combat dissolution, our findings shed light on its root causes."

Professor Kwak added, "This study is the first to demonstrate that the dissolution of electrode materials is not merely a matter of solubility but rather a function of cation-solvent interactions and ensuing mechanistic changes. We also present a targeted electrolyte design strategy."