SERS Analysis on Interfacial Reaction of Rechargeable Battery Electrode Using Plasmonic Sensor Element – SEI Formation at Graphite Electrode Surface
Authors: Kunimoto Masahiro , Sun Yingying , Yanagisawa Masahiro , Homma Takayuki 
Published: February 2020

Surface enhanced Raman scattering (SERS) effect to magnificently intensify Raman signals, provided by nano-structured metal surface or plasmonic nano particles, is a powerful tool for analyzing interfacial phenomena on the electrodes [1,2]. To produce this SERS effect handily in practical analyses of solid-liquid interfacial reaction at the electrode, we have developed optical components made of transparent materials with nano particles of plasmon-active metals (Ag, Au, etc.), which we call as “SERS sensor” [3]. Just locating this sensor onto the electrode surface magnifies the Raman signals about chemicals at the electrode, providing the information to investigate the interfacial reaction phenomena. We employs this SERS measurement technique to reaction mechanism analyses for electrode surfaces.
One of our present targets is the reaction behavior at electrodes in Li ion secondary battery (LIB), focusing on formation mechanism of solid-electrolyte interface (SEI) [4]. SEI formation is one of the critical factors to determine the performance of LIB [5,6], which could avoid farther decomposition of electrolyte, while permitting Li+ to penetrate. Such properties of SEI films strongly depend on the composition of the film itself, which is determined by unclear mechanism of SEI formation. To understand the SEI film formation mechanism in the LIB in detail, Raman spectroscopy including highly precise SERS measurements was performed. Here, Li2CO3 generation was particularly focused on, whose formation mechanism is not clear in spite of its critical roles in the SEI films. Two kinds of solvent were used as electrolytes: mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with 1:1 in volume, called as EC-EMC, and mixture of propylene carbonate (PC) and EMC with 1:1 (v/v), PC-EMC. This is because these two organic solvents, EC and PC, show clearly different performances on SEI formation. The graphite anode and the LiCoO2thin film cathode composed LIB model cell systems.
SERS measurements using the SERS sensor revealed clear difference between EC-based and PC-based electrolytes for the SEI formation behavior. Formation of Li2CO3 in the SEI film was not detected in EC-EMC, while that appeared in the case of PC-EMC, which should be due to the difference in the electrolyte distribution; PC-based electrolytes locate relatively lower amount of PC at the graphite electrodes than the amount of EC at the electrode in the case of EC-EMC, which leads to 2-electron reduction mechanism of SEI formation, resulting in Li2CO3formation.
Acknowledgements
This research was partially supported by the “Development of Systems and Technology for Advanced Measurement and Analysis”, and the “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING II)” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.
References:
[1] K. S. Joya, X. Sala, In situ Raman and surface-enhanced Raman spectroscopy on working electrodes: spectroelectrochemical characterization of water oxidation electrocatalysts, Phys. Chem. Chem. Phys., 17 (2015) 21094.
[2] C. M. Hill, A. Clayton, S. Pan, Combined optical and electrochemical methods for studying electrochemistry at the single molecule and single particle level: recent progress and perspectives, Phys. Chem. Chem. Phys., 15 (2013) 20797.
[3] M. Yanagisawa, M. Saito, M. Kunimoto, T. Homma, Transmission-type plasmonic sensor for surface-enhanced Raman spectroscopy, Appl. Phys. Express, 9 (2016) 122002.
[4] Y. Sun, M. Yanagisawa, T. Homma, In-Situ Raman Spectroscopy Study on the Preferential Adsorption of Electrolyte Species on Electrode Surface of Lithium Ion Battery, ECS Meeting Abstract, MA 2016-02 (2016) 1596.
[5] V. A. Agubra, J. W. Fergus, The formation and stability of the solid electrolyte interface on the graphite anode, J. Power Sources, 268 (2014) 153.
[6] P. Verma, P. Maire, P. Novak, A review of the features and analyses of the solid electrolyte interphase in Li-ion batteries, Electrochim. Acta, 55 (2010) 6332.