Quantifying the Inactivation of Battery Electrode Material Particles

Abstract

Lithium ion batteries, like any other battery technology, tend to lose capacity with continued charging and discharging. One of the effects contributing to the decline in capacity is the inactivation of positive electrode material particles. The electrodes typically consist of polydisperse active material particles, a conductive agent and a binder. By charging and discharging of the battery the active material particles are lithiated and delithiated. If a particle becomes inactive, e.g. by losing the electronical contact or by the formation of ion blocking surface films, it stops following the lithiation and delithiation of the rest of the electrode. Analyses of the degree of lithiation (DOL) of single particles therefore provide valuable information on the capacity loss attributed to inactive particles.[1-3]Since TOF-SIMS and synchrotron-based techniques which are usually used to determine the lithium content of single electrode particles only analyze small areas of the electrodes and are not well suited for measuring large numbers of samples, a method has been developed applying common ICP-OES instrumentation. For the determination of the DOL of single particles, the most important advantage of many ICP-OES instruments is the simultaneous detection of several elements. In case of common positive electrode materials such as Li(NixMnyCoz)O2 (x+y+z=1) (NMC) the ratio of e.g. Li to Mn signal intensities can be used to determine the DOL. As an aqueous sample introduction cannot be used because these materials would undergo Li+/H+ exchange reactions, a sample introduction using argon gas that furthermore enables a classification of particle sizes was developed.This presentation will focus on the method development and application of single particle ICP-OES for battery materials. It will be shown how this method helps to elucidate the mechanisms of capacity fading, and the advantages and disadvantages of ICP-OES will be compared with those of alternative methods for this application. Different parameters affecting the inactivation of poly- and single-crystallin NMC particles will be discussed.[1] T. N. Kroger, S. Wiemers-Meyer, P. Harte, M. Winter, S. Nowak, Analytical Chemistry 2021, 93, 7532-7539.[2] T.-N. Kröger, P. Harte, S. Klein, T. Beuse, M. Börner, M. Winter, S. Nowak, S. Wiemers-Meyer, J. Power Sources 2022, 527, 231204.[3] Kröger, T.-N.; Wölke, M. J.; Harte, P.; Beuse, T.; Winter, M.; Nowak, S.; Wiemers-Meyer, S. Chemsuschem 2022, 15, e202201169. Figure 1