The peak areas can be evaluated to give a quantitative element analysis of the outermost atomic layer. Light surface atoms (green) appear at low energy, whereas heavier atoms give rise to a peak at high energy. The measured energy of the scattered ions is a measure for the mass of the surface atom. The analysis with noble gas ions, that are neutralized (and undetectable even after scattering) when they enter the sample, makes sure that the analysis is limited to the outermost atomic layer.įigure 1 : Principle of a LEIS analysis: Noble gas ions are aimed at the surface where they collide with atoms. By measuring the energy of the scattered ions, the surface atoms can be identified and their concentration quantified. It exploits the fact that the velocity (energy) of an object (probe ion) after a collision depends on the mass of the object it collided with (surface atom). The principle of a LEIS analysis is illustrated in figure 1. It makes it the ideal technique to analyze the closure of coatings on cathode materials. This enables the analysis of cathode material with LEIS. The LiCarbEx procedure, developed at the Tascon laboratory, is able to remove these layers, without significantly damaging the coating. Unfortunately, in practice, these cathode materials are covered with a layer of Li 2CO 3 and LiOH. Low Energy Ion Scattering (LEIS) is a chemical analysis technique with an information depth of 1 atomic layer (~0.3 nm). An analysis technique that is more surface specific than XPS is needed. This closure of the coating is often studied by techniques like XPS and SEM/EDX, though their analysis depth (~ 2 nm for XPS and ~ 2 µm for EDX) is too high. It is important that these coatings are both closed (to prevent the dissolution of cations) and as thin as possible (to allow transport of Lithium ions to the cathode material). To prevent this, a protective coating is applied to the cathode material. One of these is the dissolution of cations into the electrolyte. The life time (number of charge-discharge cycles) of these cathode materials is reduced by degradation processes. A range of different transition metal oxides are used as cathode material: Lithium Cobalt Oxide (LCO), Lithium Manganese Oxide (LMO), Lithium Nickel Cobalt Aluminum Oxide (NCA) and Lithium Nickel Manganese Cobalt Oxide (NMC). They found their way in mobile devices, power tools, electric vehicles and power grid energy storage. The applications of Lithium ion batteries are continuously expanding.
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