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Development of Rechargeable Organic Batteries by Using Porous Organic Framework

The joint research team of Professor Hye Ryung Byon and Professor Woo Youn Kim in the KAIST Chemistry and KAISTInstitute for Nanocentury is opening a new horizon in the field of organic rechargeable batteries. The team developed lithium-organic hybrid batteries having excellent cycle performance by using a porous organic framework. Conventional rechargeable batteries, used as essential components of mobile phones, laptops and personal computers, have been manufactured with only inorganic materials such as lithium cobalt oxides (LiCoO2). However, the resource limitations of the key inorganic materials, such as cobalt and nickel, are increasing the cost of production. Moreover, despite the attractive use stability, inorganic batteries are heavy.
“If we change the materials for lithium-ion batteries to hydrocarbon organic materials, we can make lightweight and foldable batteries, which can be used in various applications.” However, despite the advantages that Professor Byon introduced, there must have been reasons organic batteries could not be developed yet, and the obstacles must have been the focus of their work.

|Dreaming of Organic Material Innovation in Batteries |

The key was design of organic molecules and their ordering structure to improve insolubility, stability, and conductivity.
The point of their results, published in Advanced Energy Materials (May 2021, Vol. 11, Issue 17), a globally acclaimed journal, was the design of the porous organic framework. The system was designed to overcome the vulnerability of single organic molecules in terms of solubility, stability, structurization, and conductivity, compared to the existing inorganic batteries. The research team constructed a huge porous organic framework by employing, as a redox (reduction and oxidation) core, an azo group (N=N), having a double bond between two nitrogen atoms, and intertwining molecules with benzothiazol linkers.
“Organic molecules have different properties from the inorganic materials. When a battery is operated, organic molecules become highly unstable, as they are dissolved into the liquid electrolyte or their bonds are broken by the redox reactions . The organic framework was designed by tying these organic molecules to overcome above problems. The intermolecular interactions and electronic structures, controlled during the establishment of the framework, were studied to improve the chemical stability, insolubility and electric/ionic conductivity.”
The framework has the characteristics of a porous crystal in which two-dimensional films can be formed through the covalent bonding of organic molecules and they can grow three-dimensionally through their pi-pi bonding. The pores having typically around 2~3 nm allow lithium ions to move in and out of the framework so that the framework can function as a Li ion-permeable organic electrode. Electron coupling through vertical p orbitals of the azo group towards out of the plane of the framework also improves electronic conductivity.

Fast charge and long-term cycling of organic electrode in Li ion batteries
Using the porous organic framework, the research team developed an organic electrode that can be operated over 4,500 cycles at a high charge/discharge speed with one cycle in 6 minutes. However, leaving the encouraging accomplishments behind, Professor Byon is endeavoring to conduct studies in anode to supplement the present work focused on cathode and to develop solid electrolytes by designing porous organic frameworks further. Her voice is calm but is full of confidence, representing the significance of the present research accomplishments.
“What really matter is the material that we choose and the kind of framework that we prepare. This requires not simply the attempts for combining different organic molecules but the fundamental understanding of the chemical and electrical properties of the organic framework. We are looking forward to replacing the inorganic materials in batteries and displays through the collaborative works in various analyses and calculations.”
Prof.Hye Ryung Byon
2021 Annual Report

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