Investigating Electronical Contact Loss Between LIB Cathode Particles by ICP-OES

摘要

Mechanical degradation phenomena occurring during charging and discharging can severely affect the electronical contact among the particles within the composite cathode material (e.g. LiNi[1/3]Mn[1/3]Co[1/3]O[2] (NMC111)). In particular, the application of high C-rates results in mechanical strain facilitating the disintegration of active material particles from the conductive network and therefore leading to a deterioration of the electrochemical performance.There is a large variety of monitoring and investigation techniques for the analysis of electrode materials (e.g. impedance spectroscopy, X-Ray Diffraction, Raman spectroscopy). These techniques provide mean values of certain fractions of the bulk or surface material. However, the analysis of electronical contact loss requires investigations on particle level. Therefore, the development of novel analytical approaches for the investigation of particle contact loss and the resulting contribution on the capacity fading is mandatory. The focus of this work is the development of a method for single particle analysis of lithium ion battery (LIB) cathode materials by means of inductively coupled plasma optical emission spectroscopy (ICP-OES). For this application, ICP-OES outweighs other techniques due to the elemental specificity, selectivity and a simultaneous detection of several analytes.Presuming an intact conductive network within the electrode, the state of charge (SOC) of every active material particle should be equal. Since the SOC correlates with the degree of lithiation (DOL) of the particles, the assessment of electronical contact is accessible by determining the ratio of lithium and host element (e.g. nickel, cobalt, manganese) on a particle level by ICP-OES.