Abstract text (incl. figure legends and references)

Energy storage and conversion technologies are key technologies for the future on the way of "going green". The quantification of Li and limited spatial resolution of EDS analysis are bottlenecks to overcome. There the spectroscopy of low energy x-rays with the windowless Oxford extreme EDS detector open new prospects. This enables to reduce the accelerating voltages and/or beam currents and therefore additionally radiation damage. Fig 1a) show spectra of Li metal, where the grey spectrum is recorded directly after the transfer from the glove box to the SEM and the red spectrum after 9 days storage at air. The significant changes of the Li peak content, shape and peak position document the sensitivity and reactivity of Li, exemplary to air exposure. One sensitive part in Li-Ion batteries is the interface between the anode and the separator with the solid electrolyte interface covering the anode surface and eventually with reaction products on top. Fig. 1 b), c) show such reaction products of a Li-Ion battery with a LiFePO4 cathode and a carbon anode. The EDS spectra show significant enrichment for the dark surface coated areas on top of the massive anode encrustation spectrum16 and the round shaped particle spectrum 17. This enables to determine precipitations, which reduce the amount of Li inventory and on this way the battery performance. Starting quantification consistently upcoming questions are: How reliable are EDS studies for real life application and what are the influences of etc. sample preparation. Therefore a systematic study was performed on Li(NixMnyCoz)O2 cathode material and the first topic was the determination of the stoichiometric composition of Ni, Mn and Co, where Ni, Mn and Co share one position, therefore x+y+z=1. Fig, 2 a) shows the results for studies obtained with different sample treatment like:

shuttle => argon atmosphere and SEM vacuum, top view air => in air, top view gold => in air and coated with gold ( 4 nm), top view carbon => in air and coated with carbon (10 nm), top view cross section => in air cross section obtained with an argon ion mill

All performed studies (Fig. 2) deliver a stoichiometric relationship close to NMC (811). This shows the robustness of the performed studies. One limitation for the chemical quantification of Li-Ion battery materials is, that bonded Li cannot directly detected by EDS. We determine the Li amount as the missing element fraction of not normalized quantitative EDS analysis. Precondition is that during the measurement no dynamic processes like contamination, radiation damage, charging etc. are taking place. Additionally we solely take those spectra for the quantification into account, where the oxygen weight percent of the EDS spectra is ±3% of the expected weight percent for oxygen in Li(Ni8Mn1Co1)O2 . We obtained mean values of the Li weight percent for the analytic conditions: 1. shuttle: 6,0±0,5% ; 2. air: 6,1±0,8% ; 3. gold: 10,6±0,8% ; 4. carbon: 10,4±0,7% and 5. cross section: 6,4±0,6%. The expected value for a 100% lithiated cathode material is 7,1%, where this value overestimate the real content and will be reduced by approx. 10% formation loss after the first battery cycle. The results of the studies performed with the conditions 1, 2, 5 agree nicely with the expectation, where the gold and carbon coating lead to a significantly overestimation of the Li content. [1]

[1] The authors gratefully acknowledge the German BMBF for financial support.