Interfacial resistance between the cathode layer and the current collector in lithium-ion batteries

Significance 

Shortchanged by the realization of the consequences of carbon emissions, a global trend towards hybridized and electric vehicles is rapidly gaining popularity. Electric vehicles mainly use lithium-ion batteries (LIBs). This application demands that the LIBs have a high energy density and high-power density. To meet such demands, the operating voltage of LIBs must be increased and their internal resistance must be decreased. For the former, lithium metal anodes and high-voltage cathodes have been proposed while as for the latter, technical hinderances have been encountered. To be specific, the electrical conductivity of transition metal oxides for cathodes has proven insufficient, compared with that of carbon materials for anodes. This can however be resolved through the addition of electroconductive materials in the cathode layer. Electrochemical impedance spectroscopy (EIS) has been a powerful tool for evaluating the decrease in the interfacial resistance between the electrode layer and the current collector. Generally, cathode impedance, which is measured by EIS, comprises a surface film resistance on an active material, a charge transfer resistance, and a diffusion impedance. However, depending on the preparation conditions of the cathode, the cause of characteristic high frequency is occasionally different.

Recently, Waseda University researchers led by Professor Tetsuya Osaka from the Graduate School of Advanced Science and Engineering reported a study in which they investigated the interfacial resistance between the cathode layer and the current collector observed at high frequencies, which generally is attributed to a resistance of surface film like solid electrolyte interphase. They focused on using EIS to study LIBs with different cathode densities but with the same active material loading, and LIBs with or without an interlayer between the cathode and the current collector. Their work is currently published in the research journal, Journal of Power Sources.

To investigate the interfacial resistance systematically, different interfaces between the cathode layer and the current collector were prepared by controlling the press rate for the cathode preparation, or by introducing a carbon under-coating layer, followed by electrochemical impedance spectroscopy.

The authors observed that the interfacial resistance between the cathode layer and the current collector prepared with an insufficient press rate or without a carbon under-coating layer was extremely high for the entire cathode. In addition, from the cathode cross-sectional observation, they noted that the high interfacial resistance was caused by low contact rate at the interface. Using a pouch-type symmetric cell, EIS revealed that the interfacial resistance could be attributed to electric resistance, that is, contact resistance at the interface. Also, the other resistances were attributed to be the ionic resistance of the electrolyte and pores in the cathode, and the charge transfer resistance of the cathode.

In summary, the Hiroki Nara and colleagues looked carefully at the impedance observed at high frequencies, which is generally attributed to a surface film resistance. Generally, the effectiveness of the carbon under-coating layer was shown to decrease the cathode impedance. The effectiveness of carbon coating on the current collector was thus demonstrated. Altogether, this is the first study to report the discussion of the activation energy of the interlayer resistance for LIBs.

Systematic analysis of interfacial resistance between the cathode layer and the current collector in lithium-ion batteries by electrochemical impedance spectroscopy - Advances in Engineering

About the author

Tetsuya Osaka is Senior Research Professor and Emeritus Director of the Institute for Research Organization for Nano & Life Innovation, and Professor Emeritus of the Faculty of Science and Engineering, Waseda University, Tokyo, Japan. He is past President of the Electrochemical Society (ECS), also was serving as President of the Magnetics Society of Japan, President of the Electrochemical Society of Japan, President of Japan Institute of Electronic Packaging, Vice-President of the Surface Finishing Society of Japan, Vice President of the International Society of Electrochemistry (ISE).

The recent works focus on a newly “electrochemical nanotechnology”. His technical contributions have been recognized by many awards including Medal with Purple Ribbon bestowed from the Decoration Bureau of the Cabinet Office, Japan, in 2010, Prizes for Science and Technology in Development Category of the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology in 2008, and so on.

His research field is electrochemical technology, and his recent work is focused on electrochemical nanotechnology, including electro- and electroless-deposition/surface finishing, electronic packaging materials, magnetic storage and energy storage devices, and chemical- and bio-sensors. Especially, he nowadays focuses on batteries and battery energy managing system. He has contributed as an author and/or editor to more than 90 books and published more than 1000 original and review papers in these fields. He has been identified as one of the Highly Cited Researchers in the Materials Science category in Thomson ISI’s ISIHighlyCited.com.

About the author

Hiroki Nara received his PhD degree in electrochemistry from Waseda University, Tokyo, Japan in 2008. From 2007 to 2009, he worked as a research associate, and then from 2010 to 2016 as an assistant professor in Waseda University. Currently, he is an associate professor of Research Organization for Nano & Life Innovation, Waseda University, Tokyo, Japan. His research interests focused on electrochemical energy devices. Especially, he is working on electrochemical impedance spectroscopy (EIS) analysis for electrochemical energy devices, such as lithium-ion batteries (LIBs), all solid-state LIBs, and polymer electrolyte fuel cells, in which reaction site are distributed due to ionic- and electric-resistance in electrodes and due to variation of particle size of active materials. He is also working on battery materials, such as alloy-based anodes (Sn and Si), conversion cathodes (sulfur, and so on), electrolytes (polymer and solid).

ORCID

About the author

Daikichi Mukoyama received the Ph.D. degrees in Biotechnology and Life-Science from the Tokyo University of Agriculture and Technology, Tokyo, Japan, in 2007. He is an Associate Professor of Research Organization for Nano & Life Innovation, Waseda University, Tokyo, Japan. He has been on research member with Waseda University since 2007. His current works include battery diagnosis using electrochemical impedance spectroscopy and management of technology for the social contribution.

Dr.Mukoyama strongly believes that a correct diagnosis of batteries will lead to the highly reliable service for the diversified social environment.

About the author

T. Momma

Professor, Department of Applied Chemistry and Department of Nanoscience and Nanoengineering, Faculty of Science and Engineering, Waseda University.

Working as Professor, Dept. of Appl. Chem/NanoSci. And NanoEng., Waseda Univ. from 2014. He served as the Dean Assistant of Faculty of Science and Engineering, Waseda Univ. in 2014-2016. He was the Chief Prof. of Dept. of NanoSci. and NanoEng., Waseda Univ. in 2017-2018. From 2018, currently he is serving as the Chief Prof. of Dept. of Appl. Chem., Waseda Univ.

His educational background is as follows. He got Ph. D degree in 1995 from Graduate School of Science and Engineering, Waseda Univ. (Dr. of Eng., Waseda Univ.) after graduation from School of Science and Engineering, Waseda Univ. in 1990.

His research interests are in the fields of electrochemical energy devices, bio-electrochemical sensors and electrochemical methods. He is working on materials of electrodes and interface design for rechargeable batteries including electrochemical systems for future batteries. He is working on electrochemical sensors including FET sensors and amperometric sensors. He is also interested in the development and improvement of electrochemical impedance spectroscopy.

He is currently working on the in situ electrochemical impedance analysis of rechargeable batteries and electrochemical interfaces as non-destructive diagnosis of the devices.

Reference

Hiroki Nara, Daikichi Mukoyama, Ryo Shimizu, Toshiyuki Momma, Tetsuya Osaka. Systematic analysis of interfacial resistance between the cathode layer and the current collector in lithium-ion batteries by electrochemical impedance spectroscopy. Journal of Power Sources, volume 409 (2019) page 139–147.

Go To Journal of Power Source

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