Korea University: Development of bottlebrush polymer-based binders for high mass-loading cathodes

Professor Bang Joona’s group from the Department of Chemical and Biological Engineering, College of Engineering at KU collaborated with Professor Lee Sang-young’s group from the Department of Chemical and Biomolecular Engineering at Yonsei University and developed amphiphilic bottlebrush polymer-based binders for high mass-loading cathodes, which are essential to the development of high-energy lithium-ion batteries.

The results of their study were published in the online edition of Advanced Energy Materials (Impact Factor: 29.368), a globally acclaimed journal in the field of energy materials, on November 21.

The demand for high-energy density lithium-ion batteries continues to increase worldwide. With environmental friendliness issues and the related growth of the electric vehicle (EV) market, studies are being carried out to develop effective active materials that can satisfy EV high voltage conditions, which include high capacity and rapid charging/discharging of lithium-ion batteries. However, in contrast to the remarkable development of the active materials used in electrodes, the development of polymeric binders, another essential material for electrodes, has been relatively sluggish. With regard to the electrodes manufactured to realize high energy density, the application of the conventional binders, such as PVDF, presents several problems, including a decrease of dispersity and low adhesiveness. This has resulted in an emerging need for developing new functional binder materials to form uniform electron/ion conduction networks or for maintaining sufficient adhesion between electrode active layers and current collectors.

Professor Bang’s group has overcome the problems of the existing cathode polymeric binders by designing an amphiphilic bottlebrush polymeric binder as a new binder material. The amphiphilic bottlebrush polymeric binders are three-dimensional polymers consisting of hydrophobic polynorbornene (PNB) backbones and hydrophilic polyacrylic acid (PAA) side chains. The three-dimensional bottlebrush structure allows the polymers to be effectively dispersed in an electrode. As the polymers are not easily degraded during charging/discharging, stable performance can be achieved. In addition, the amphiphilicity of the backbones and sidechains minimizes the volumetric expansion caused by the electrolyte, and the hydrogen bonding with aluminum current collectors provides strong adhesion. As a result, the group formed uniform electron/ion networks and developed cathode binders demonstrating excellent electrochemical and physical performance.

The group used the amphiphilic bottlebrush polymeric binders in a very low content (1 wt%) to fabricate a high mass-loading electrode having a 27 mg cm-2 areal mass loading and 5.2 mAh cm-2 areal capacity, and the performance of the electrode was stably maintained, even during repeated charge/discharge cycles. The performance shown was far better than that of previous studies. This indicates that the structural specificity and chemical functionality of the amphiphilic bottlebrush polymers can act very effectively when the polymers are applied as cathode binders.

Professor Bang commented, “Our study is significant in that the newly developed essential binder material can effectively replace the conventional liner polymer binders such as PVDF.” He added, “We expect that our results can be used to facilitate the development of high-energy density lithium-ion batteries, enhancing the advancements in the relevant industries, including the EV and energy storage system (ESS) industries.”

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