Powder Structure Control Technology in the Solvent-Free Dry Electrode Forming Process of Lithium-Ion Battery and Its Battery Performance Evaluation
Authors: Tuerxun Feilure , Yonaga Ayaka , Kawauchi Shigehiro , Matsunaga Takuro , Nakamura Hiroshi , Mori Yuki , Ishikawa Shota , Nunoshita Keita , Inoue Gen , Liu Xuanchen 
Published: December 2024

Lithium-ion batteries (LIBs) are widely used as power sources for electrified vehicles because of their high energy density and power density. As demand for LIBs increases rapidly, improving the manufacturing process of making LIBs is a key to further decreasing the cost and expanding the market of LIBs for many applications, especially for electric vehicles. Electrodes for LIBs are generally manufactured by the slurry-based electrode forming process, in which active materials (AMs), conductive and binding additives (CBA) are dispersed in a solvent, and the material prepared as a slurry is coated onto a current collecting foil, followed by drying to remove the solvent. Although this slurry-based electrode forming process is a simple way to form electrodes but requires a large amount of energy for the drying process because the solvent must be evaporated at high temperatures in a drying oven. Furthermore, N-methyl-2-pyrroidone (NMP), which is the most common solvent for cathode slurries, must be recovered and processed due to its high toxicity. To meet these requirements, a solvent-free dry electrode forming process have been proposed to reduce environmental impact and cost in the electrode manufacturing process. Since dry electrode forming processes require no solvent from electrode material mixing steps to an immobilization step on a collector foil, there is no need to either dry or recover solvents. Therefore, the dry electrode forming processes can significantly reduce the material cost and energy consumption in battery manufacturing.

From the viewpoint of the battery performance, the electronic and ionic conduction within the electrode is affected by the internal structure of the electrode, the composition and distribution of the CBA within the electrode, as well as the shape, connectivity, and volume fraction of pores within electrodes. In the slurry-based electrode forming process, it is difficult to control the distribution of CBA due to interactions in the slurry, such as the binder migration phenomena during drying. In contrast, the dry electrode forming process directly fabricates electrode films from electrode powder mixture, which consists of the AM and CBA. As a result, the electrode structure can directly reflect the morphology of the electrode powder without being affected by the binder migration phenomenon. Therefore, dry electrode forming processes have big potential for not only reducing the manufacturing cost but also controlling electrode structure and thus designing battery performance. However, there is little discussion regarding the optimal morphology of electrode powder mixture to improving battery performance for dry electrode forming process.

Therefore, in this study, we propose a method for designing the optimal morphology of the electrode powder for improving the battery performance. We investigate how the morphology of the electrode powder mixture affects the structure and battery performance of lithium-ion battery electrodes fabricated using the dry electrode forming process. We demonstrate that the distribution of conductive additives and binders (CBA) on the active material (AM) can be controlled by adjusting the rotation speed of the dry mixer. Furthermore, we show that the rate performance of the battery can be improved by controlling the distribution of CBA. We also discuss the internal structure of the electrodes, especially focusing on the electronic and ionic conductive pathways, to elucidate the relationship between the electrode structure and battery performance.