Successful Development of an Operando Microscope Capable of Simultaneous Measurement of Local Electrochemical Reactions and Raman Spectroscopy Information

The research group led by Professor Akiya Kumagai (Chiba Institute of Technology, Faculty of Engineering, Department of Electrical and Electronic Engineering / Tohoku University, WPI-AIMR Visiting Professor) and Graduate School of Engineering Visiting Professor, Eita Tatezaki (Chiba Institute of Technology, Graduate School of Engineering, 1st year master's student), Ryunosuke Ishige (Chiba Institute of Technology, Graduate School of Engineering, 1st year master's student), Lecturer Daiki Ida (Nagoya University, Graduate School of Engineering), Professor Yasufumi Takahashi (Nagoya University, Graduate School of Engineering (concurrently Institute for Advanced Research, Quantum Chemistry Innovation Research Institute) / Kanazawa University, NanoLSI Specially Appointed Professor), Professor Sho Shiraki (Nippon Institute of Technology, Faculty of Engineering Sciences, Department of Environmental and Life Chemistry), and Professor Hitoshi Shiku (Tohoku University, Graduate School of Engineering) has developed a novel operando measurement method that integrates Raman spectroscopy (Note 1) and scanning electrochemical cell microscopy (SECCM) (Note 2). In electrochemical energy devices such as lithium-ion batteries and electrode catalysts, reactions at the solid-liquid interface are critical factors that determine performance and durability, and understanding the electrochemical processes progressing at the interface at the nanoscale is required. Previously, it has been difficult to simultaneously observe local electrochemical reactions and accompanying structural changes during operation (operando) using measurement techniques such as Raman spectroscopy. Typically, in simultaneous measurements of electrochemical reactions and spectroscopic methods, the electrochemical reaction field is conducted by immersing the sample in an electrolyte solution, which only yields averaged information over a wide reaction area, leading to a lack of local information. The newly developed simultaneous operando measurement method integrates Raman spectroscopy and SECCM. The research group successfully used lithium iron phosphate (Note 3), an electrode in lithium-ion batteries, to localize the reversible electrochemical reaction of lithium ions within the microdroplet formed by SECCM, while measuring changes in the chemical structure within that region using Raman spectroscopy, which evaluates scattered laser light. From the obtained results, local chemical structural changes during the de-insertion and insertion processes of lithium ions from the lithium iron phosphate electrode within the droplet were confirmed by observing Raman scattered light.

The development of this microscope enables simultaneous operando measurement of local electrochemistry and chemical structure changes, succeeding in analyzing interface reactions of electrochemical reactions at the nanoscale. This is expected to contribute to elucidating the degradation mechanisms and reaction heterogeneity of lithium-ion batteries, providing new insights that offer design guidelines for high-performance, long-life batteries. Furthermore, this method is expected to become a new fundamental technology that enables nanoscale understanding of all solid-liquid interfaces involved in electrochemical reactions, not only in lithium-ion batteries, but also contributing to the advancement of basic science in the battery, catalyst, and corrosion fields.

This research achievement was published on April 21 (US time) in Applied Physics Letters, an academic journal in the field of applied physics by the American Institute of Physics (AIP), and was selected as a "Featured Article". This paper was also featured and explained in "Scilight", an AIP public relations medium that highlights notable achievements from across AIP journals.

Keywords: Operando measurement, Electrochemistry, Lithium-ion battery, Raman spectroscopy

■ Background of Research

1. Understanding Solid-Liquid Interfaces in Electrochemical Energy Devices

Towards the realization of a carbon-neutral society, the importance of electrochemical energy devices such as lithium-ion batteries, hydrogen/ammonia synthesis, and electrochemical reduction of carbon dioxide is increasing. To improve the performance of these devices, material development, along with atomic-level structural control, is indispensable. However, as the microstructure of materials becomes highly controlled, electrochemical reaction mechanisms become more complex, requiring a detailed understanding of their effects. In particular, electrochemical reactions proceed at the solid-liquid interface where the electrode and electrolyte meet, making an understanding of the reaction processes at this interface key to device performance. However, since reactions at the solid-liquid interface proceed non-uniformly in time and space, high-precision in-situ operando analysis is required.

2. Conventional Analysis Methods and Their Challenges

At the solid-liquid interface, electro...