Method development for direct elemental analysis of lithium ion battery materials by means of ETV-ICP-OES

Kessen, Dennis; Walter, Matthias; Winter, Martin; Nowak, Sascha; Wiemers-Meyer, Simon

Abstract

Method development for direct elemental analysis of lithium ion battery materials by means of ETV-ICP-OES Dennis Kessen1,*, Matthias Walter1, Martin Winter1,2, Sascha Nowak1, Simon Wiemers-Meyer1,‡ *dennis.kessen@uni-muenster.de ‡simon.wiemers-meyer@uni-muenster.de 1University of Münster, MEET Battery Research Center, Corrensstraße46, 48149 Münster, Germany 2Helmholtz-Institute Münster, IEK-12, FZ Jülich, Corrensstraße46, 48149 Münster, Germany In the last three decades, lithium ion batteries (LIBs) have undergone an impressive development and are an integral part of our modern society through their use in portable consumer electronics and the emerging electromobility. The overall aim of achieving higher energy densities and lower material costs has led to the continuous development of new cell chemistries, specifically adapted to the various applications.[1] However, the LIB still suffers from capacity loss due to several aging mechanisms while cycling and storage. The electrolyte is not stable at the occurring electrode potentials and forms passivating layers on anode and cathode, the so called solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), respectively. These interphases consist of various inorganic lithium salts as well as organic carbonates and phosphates. Structural instability of the cathode active material (lithium transition metal oxide) leads to dissolution of Ni, Co and Mn, which deteriorate the SEI and lead to irreversible lithium loss on the anode. [2] Elemental analysis, particularly inductively coupled plasma-optical emission spectroscopy (ICP-OES), plays a crucial role in deciphering these aging mechanisms. High requirements are placed on the analysis system for the simultaneous quantification of elements in different concentration ranges from sup-ppm to several percent with high matrix loads. Direct elemental analysis of LIB materials by coupling electrothermal vaporization (ETV) to ICP-OES offers distinct advantages over conventional microwave-assisted digestion approaches. By avoiding the time-consuming and labor-intensive digestion step, analysis time can be significantly reduced, which is accompanied by less risk of cross-contamination and a potential gain in sensitivity and accuracy.[3] Regarding LIB samples, cathode coatings and dopants of compounds like SiO2 and ZrO2 or silicates in anode materials are hard to digest, where direct sample introduction by thermal vaporization could be beneficial. Furthermore, temperature programming might offer possibilities for speciation analysis of the SEI. Aged anode samples from Li1Ni0.8Mn0.1Co0.1 NMC811||artificial graphite + 10 % SiOx and NMC111||artificial graphite cells were analyzed regarding there Li, Ni. Mn and Co content as well as possibilities for SEI speciation. Method development for the analysis was performed on an ETV (ETV 4000c, Spectral Systems, DE), equipped with an autosampler (AD-50-III, Spectral Systems, DE), which was directly coupled to an ICP Spectrometer (ARCOS, Spectro Analytical Instruments, DE). Sulfur hexafluoride was used as modifier gas. External calibration of the instrument was performed using liquid standards (LabKings B.V., NLD), synthesized matrix-matched standards or certified reference materials, while the Ar 763.5 nm line was used for internal standardization. The analytical performance of the developed method was evaluated by comparison to microwave-assisted ICP-OES and total reflection X-ray fluorescence (TXRF) measurements. As very high lithium contents in the samples had an influence on the plasma conditions, further preliminary experiments using solid sample dilution and dilution of the sample gas flow by an additional sheath gas were performed. Keywords lithium ion battery, ETV-ICP-OES, method development, rollover failure Acknowledgements The authors would like to acknowledge the German Federal Ministry of Education and Research (BMBF) for funding the project “E-FloA” (03XP0349B). References [1] J. Xie, Y.-C. Lu, Nature Communications 2020, 11, 2499. [2] S. Klein, S. van Wickeren, S. Röser, P. Bärmann, K. Borzutzki, B. Heidrich, M. Börner, M. Winter, T. Placke, J. Kasnatscheew, Adv. Energy Mater. 2021, 11, 2003738. [3] L. Huang, D. Beauchemin in Sample Introduction Systems in ICPMS and ICPOES (Ed.: D. Beauchemin), Elsevier, Amsterdam, 2020, pp. 411–467.