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Dr. Shuji Ohsaki

Chemical Engineering, University of Kyoto

shuji.ohsaki@omu.ac.jp

Dr. Shuji Ohsaki is an Associate Professor in the Department of Chemical Engineering at Osaka Metropolitan University. He completed his Bachelor, Master, and Doctor of Engineering degrees at Kyoto University between 2008 and 2017. Dr. Ohsaki was awarded the JSPS Research Fellowship for Young Scientists during his PhD studies.

From 2017 to 2022, he served as an Assistant Professor at Osaka Prefecture University, focusing on both teaching and research. His work has earned him several honors, including the Young KONA Award at the 8th Asian Particle Technology Symposium in 2021 and the 2022 Outstanding Young Researcher Award from the Society of Chemical Engineers, Japan.

With a strong commitment to mentoring and research, Dr. Ohsaki continues to advance the field of chemical engineering.

He is currently spending a sabbatical year of studies at the Technical University of Braunschweig. 

Presentation:

Powder compression and particle synthesis for all-solid-state battery

Background 

All-solid-state lithium-ion batteries (ASS-LiB) have garnered attention as the next-generation secondary batteries owing to their high safety and energy densities. The ASS-LiBs are produced by compression of inorganic solid electrolytes, instead of an organic liquid electrolyte. Therefore, interstitial voids deteriorate the battery capacity, which is a serious problem with ASS-LiBs. A straightforward solution to this problem is to fill the voids using smaller particles. However, there are insufficient studies on compression process of bimodal powders and particle size control. In this study, we used the discrete element method to investigate the effects of particle cohesiveness and plasticity on the compression of bimodal powders. Moreover, we attempted to control the particle size of battery material using a liquid phase synthesis method. 

Numerical simulation of powder compression 

The DEM is a numerical method for powder motion that considers the motion of each element based on Newton’s second law. The Edinburgh elastoplastic adhesion model, which considers particle cohesiveness and plastic deformation, was applied as the contact model. The particle plasticity λp was varied from 0 to 0.7. The macroscopic and microscopic properties of the powder compression were investigated. In contrast to that for the elastic model, the void fraction at Vf = 0.5 was smaller than that at Vf = 0.3 for the high plastic condition (λp = 0.7). In addition, as the number of fine particles increased, the largest contact type changed in the order of coarse–coarse, coarse–fine, and fine–fine. The plasticity of the particles enhanced the effects of fine particle addition. 

Particle size control via liquid-phase synthesis 

In this study, nano-sized solid electrolyte particles of Li3PS4 (LPS), which is a typical sulfide solid electrolyte, was synthesized using a liquid-phase shaking method. The nucleation rate of LPS was improved using the submicron-sized Li2S as raw material, which was prepared through wet milling and dissolution-precipitation processes. The liquid-phase shaking method using fine Li2S powder successfully synthesized nano-sized LPS particles (93 ± 34 nm) with high crystallinity and ionic conductivity. Moreover, the particle size of LPS is controlled from 93 nm to 1.4 μm by the particle size of raw material, Li2S. 

Conclusions. 

This study demonstrated that the plasticity of the particles affected both the macroscopic and microscopic powder properties. It is important to determine the optimal addition ratio of fine particles based on the plastic deformability of the material [1,2]. Also, the particle size control [3,4] must be effective in improving the performance of ASS-LiBs using high-density filling for electrodes. 

Reference. 

[1] T. Yano, S. Ohsaki, H. Nakamura, S. Watano, Adv. Powder Technol., 32, 1362-1368 (2021) 

[2] T. Yano, S. Ohsaki, H. Nakamura, S. Watano, Adv. Powder Technol., 34, 1042445 (2023) 

[3] S. Ohsaki, T. Yano, A. Hatada, H. Nakamura, S. Watano, Powder Technol., 387, 415-420 (2021). 

[4] C. Tatsuta, S. Ohsaki, H. Nakamura, S. Watano, Adv. Powder Technol., 35, 104408 (2024) 

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