Correlative Scanning Probe and Confocal Raman Microscopy for the Evaluation of Li-ion Kinetics in LiMn2O4 Cathodes
Denis Alikin a b, Boris Slautin b, Konstantin Romanyuk a, Daniele Rosato c, Alexander Tselev a, Andrei Kholkin a b
a Department of Physics & CICECO—Aveiro Institute of Materials, University of Aveiro, 3810–193 Aveiro, Portugal
b Ural Federal University, School of Natural Sciences and Mathematics, Ekaterinburg, Russia, Russian Federation
c Robert Bosch GmbH, 70839 Gerlingen-Schillerhoehe, Germany
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#MapNan19. Mapping Nanoscale Functionality with Scanning Probe Microscopy
Berlin, Germany, 2019 November 3rd - 8th
Organizer: Stefan Weber
Oral, Denis Alikin, presentation 357
Publication date: 16th July 2019

Li-ion accumulators (LIA) are extremely important for the development of energy storage systems for transport, portable appliances and mobile electronics. The studies of the LIA materials by microscopic methods play a key role in the understanding of the mechanisms of electrochemical processes at the micro- and nanoscales. Scanning probe microscopy (SPM) methods for studying LIA materials started in the beginning of 90s and evolved from the simple topographic measurements to voltage driven local intercalation-deintercalation studies [1]. Direct methods of ionic conductivity evaluation at the nanoscale, so called scanning electrochemical microscopy, are based on the measurements of ion interaction with a sample in an electrolyte media [2]. These methods require complicated sample preparation, specialized cells and probes, as well as a high homogeneity of the surface [2]. This makes their use complicated for the implementation in practical electrochemical systems.

In this work, a quantitative indirect method based on the strain response to local voltage excitation, so-called electrochemical strain microscopy (ESM), is considered. The method relies on the modulation of ion concentration in the vicinity of SPM tip [1]. To interpret the ESM data quantitatively we measure current and acoustic correlative responses allowing to estimate the voltage drop at the interface and contact stiffness, respectively [3]. Correlative confocal Raman and scanning probe microscopy approach was implemented to find a relation between the structural state and functional electrochemical response in individual micro-scale particles of LiMn2O4 spinel in a commercial Li battery cathode [4,5]. It was shown that the high-frequency ESM has a significant cross-talk with the topography due to the tip-sample electrostatic interaction, while the low-frequency ESM yields a response that can be linked to the distributions of Li ions and electrochemically inactive phases revealed by the confocal Raman microscopy. We conclude that the obtained low frequency ESM image contrast is caused by the Vegard strain and can be used  to map local Li-ion concentration and thus it is controlled by local diffusivity. The observed features of the low-frequency ESM signal distribution across the cathode are used for the interpretation of Li ion intercalation kinetics during battery degradation.

 

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. The work was financially supported by the Portuguese Foundation for Science and Technology (FCT) within the project PTDC/CTM-ENE/6341/2014. Confocal Raman microscopy was performed at the Ural Federal University (UrFU). This part of the research was made possible by the Russian Science Foundation (Grant 17-72-10144). The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used.

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