First Insights for the Investigation of the Electrical Contact Among the Particles of Lithium Ion Battery Cathode Materials

Abstract

Mechanical degradation phenomena arising from the volume change during charging and discharging can severely affect the electrical contact among the particles within the composite cathode material. Furthermore, electrochemically induced particle disintegration at high currents (e.g. for LiNi1/3Mn1/3Co1/3O2 (NMC111)) is conceivable to have a major influence on the loss of electrochemical performance. There is a variety of electrochemical monitoring and investigation techniques for the analysis of electrode materials (e.g. impedance spectroscopy, X-Ray Diffraction, Raman spectroscopy). However, there is no sensitive analytical method in the field of battery research for the investigation of particles and the integrity of the conductive network among them within the composite electrode material. Therefore, the development of novel analytical approaches for the investigation of particle contact and the resulting contribution on the capacity fading is mandatory. The focus of this work is the development of a method for particle analysis of lithium ion battery (LIB) cathode materials by means of inductively coupled plasma based techniques with optical emission spectroscopy (ICP-OES) and mass spectrometry (ICP-MS). Presuming an intact conductive network among the particles of the active material, the state-of-charge (SOC) should be equal throughout the electrode. Because the SOC correlates to the degree of lithiation (DOL) of the particles, the assessment of electrical contact is accessible by determining the ratio of lithium and host element (e.g. nickel, cobalt, manganese). For ICP-based techniques, the particle size distribution requires to be narrow and small-sized for the accurate element determination. Furthermore, due to potentially occurring Li+-H+ exchange reactions, the sample introduction of NMC cathode materials in aqueous media is not feasible[1]. Therefore, the size dependent separation is performed by the principle of air classification and the particulate sample is introduced by means of an argon flow to the plasma. The utilization of particle classification indicates the applicability for ICP-based particle analysis due to the facilitation of low particle number concentrations and narrow size distributions and the results for ICP-MS and -OES exhibit the fundamental functioning for the application in particle analysis. [1] J. Li, R. Klöpsch, S. Nowak, M. Kunze, M. Winter, S. Passerini, J. Power Sources. 2011, 196 , 7687-7691.