Post-Mortem Analysis of Commercial NMC/Graphite Li-Ion Pouch Cells within Mat4Bat European Project

Abstract

Li-ion batteries are good candidates for electric vehicles and stationary applications due to their high power and energy densities. It is well known that the lifetime of lithium ion batteries is limited by undesirable side reactions. Moreover, these side reactions can affect different parts of the battery including the electrolyte, the active material, binder, conducting agents, current collectors and the separator. Over time, this fact leads to a gradual capacity fade and the end of life of the battery. Thus, the understanding of degradation mechanisms in lithium ion batteries is considered to be of great importance. In this work, the “post mortem analyses“ of NMC/graphite commercial pouch cells has been performed. For this, a standard procedure for cell opening and preparation of the samples has been defined. As safety plays an important role in the dissemination of batteries, full discharge of the investigated cells has been carried out [1,2,3]. Furthermore, a controlled environment such as an Ar-filled glove box has been used during cell opening in order to avoid material decomposition [4,5]. Once the electrodes have been separated, the conductive salt has been removed to prevent corrosion. Diagnostic evaluation of the first degradation mechanisms has been studied by ex-situ destructive physico-chemical and electrochemical analyses of the cell components. The crystallographic and morphological studies of the electrodes have been carried out by X-ray diffraction (XRD) and electron microscopy (SEM). Additionally, elemental analysis of the electrode composition has been determined by EDS and ICP techniques. In order to evaluate the electrochemical characterization of the harvested electrodes, galvanostatic testing in half-cell configuration has been performed. The research leading to these results has been performed within the MAT4BAT project (http://www.mat4bat.eu) [1] D. Aurbach, B. Markovsky, A. Rodkin, M. Cojocaru, E. Levi, H.-J. Kim, Electrochimica Acta 47 (2002) 1899. [2] Y. Kobayashi, T. Kobayashi, K. Shono, Y. Ohno, Y. Mita, H. Miyashiro, Journal of the Electrochemical Society 160 (2013) A1181. [3] T. Waldmann, M. Wilka, M. Kasper, M. Fleischhammer, M. Wohlfahrt-Mehrens, Journal of Power Sources 262 (2014) 129. [4] H.-Y. Amanieu, D. Rosato, M. Sebastiani, F. Massimi, D.C. Lupascu, Materials Science and Engineering: A 593 (2014) 92. [5] C. Wu, Y. Bai, F. Wu, Journal of Power Sources 189 (2009) 89.