Towards better batteries and fuel cells with dispersibility estimation for carbon electrode slurries

Lithium-ion batteries are the powerhouse of modern-day electronics, and fuel cells are a promising candidate for sustainable energy devices. An important factor affecting the performance of both lithium-ion batteries and fuel cells is the dispersibility of carbon slurries, suspensions made of conductive carbon particles dispersed in a solvent. They can be easily coated on a metal collector to mass-produce electrodes. But the carbon particles in the slurry must be homogenously dispersed to ensure reliable battery performance.

However, evaluating the dispersibility of thick slurries with high particle concentrations is remarkably difficult. The large number of particles prevent peering into the internal structure of the slurries using direct spectroscopic techniques. Moreover, there are no methods to evaluate the dispersibility and conductive properties of slurries in response to shear stress applied during the coating process.    

Against this backdrop, a research team led by Associate Professor Isao Shitanda from Tokyo University of Science (TUS) in Japan developed a novel technique to estimate the dispersibility of carbon slurries. Their latest study, published online in ACS Applied Electronic Materials on 1 August 2023, is co-authored by Dr. Yoshifumi Yamagata from Anton Paar Japan K. K. and Dr. Shingo Niinobe from Shin-Etsu Chemical Co., Ltd.

The researchers combined a rheometer—a scientific instrument for measuring the flow/ deformation behavior of fluids in response to applied stress—with a spectroscopy setup to measure the electrochemical impedance of acetylene black slurries with methylcellulose (a cellulose-derived compound used as a thickener and emulsifier in food and cosmetic products, as a bulk-forming laxative and as eye/ear drops) as a dispersant. They conducted experiments under the influence of shear stress at various frequencies to obtain the rheo-impedance spectra, which provide information about the internal structure of carbon particles in a slurry. Interestingly, they noticed that the impedance spectra did not change considerably under applied shear stress for a carbon slurry with good dispersibility.

Additionally, the team developed an equivalent circuit model consisting of three types of contact resistances and capacitances: those between acetylene black particles, those of particle bulk, and those arising from the design of the measurement setup.  The bulk resistance of acetylene black showed no dependence on shear rate but decreased with increase in the methylcellulose concentration. Further, the resistance measured at each methylcellulose concentration increased with the shear rate, an observation that was attributed to a partial breakdown of the carbon–carbon network and the decreasing conductivity with rising shear rate.

Together, these results thus show that it is possible to evaluate the dispersibility of electrode slurries based on a combination of viscosity (measured with the rheometer) and electrochemical impedance measurements. Excited about the potential of their new methodology, Dr. Shitanda remarks: “The insights from this study could prove useful for improving the efficiency of large-scale electrode manufacturing processes in which the internal structure of the slurry must be carefully controlled.”

Preparing slurries with higher dispersibility could also lead to improved lithium-ion battery performance and enhanced functional materials. These would be significant contributions toward building a sustainable carbon-neutral society by fostering applications in solar panels, fuel cells, and electric vehicles.

“The proposed method can be used to evaluate the dispersibility of not just carbon dispersions, but a wide variety of slurries. In future studies, we plan to conduct further measurements and equivalent circuit verifications by changing the particle type and binder combinations,” concludes Dr. Shitanda.

Let us hope this study will enable us to produce more optimal slurries, paving the way for more sustainable technologies for next-generation electronics, electric vehicles, and energy storage devices!

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Reference                     

DOI: https://doi.org/10.1021/acsaelm.3c00612

Authors: Isao Shitanda¹, Kazuma Sugaya¹, Chihiro Baba¹, Noya Loew¹, Yoshifumi Yamagata², Keisuke Miyamoto², Shingo Niinobe³, Keiichi Komatsuki³, Hikari Watanabe¹, and Masayuki Itagaki¹

Affiliations:     

¹ Tokyo University of Science

²Anton Paar Japan K. K.

³ Shin-Etsu Chemical Co., Ltd.

About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.

With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society,” TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.

Website: https://www.tus.ac.jp/en/mediarelations/

About Associate Professor Isao Shitanda from Tokyo University of Science
Dr. Isao Shitanda graduated from the Tokyo University of Science (TUS) in 2001 and received a Ph.D. from The University of Tokyo in Japan in 2006. Since 2012, he has been an Associate Professor at the Department of Pure and Applied Chemistry at TUS, where he leads the Itagaki/Shitanda lab. He specializes in electrochemical micro/nano systems, physical and analytical chemistry, bio-related chemistry, and environmental chemistry, among other fields. He has published over 180 papers and holds seven patents.

Funding information
This work was partially supported by JSPS KAKENHI, grant number 21H03344.