Lithium-ion batteries: direct solid sampling for characterisation of black mass recyclates using graphite furnace atomic absorption spectrometry†

In this work, the potential for direct major component analysis of lithium–nickel–manganese–cobalt oxide variants in solid samples by graphite furnace atomic absorption spectrometry (SS-GF AAS) was critically evaluated, always with the aim of developing a simple and rapid method that relies only on the use of aqueous standards for calibration. The accuracy of the developed method was evaluated against an established wet chemical acid digestion method using an inductively coupled plasma optical emission spectrometer (ICP-OES). The most challenging aspect was the selection and use of suitable standards, whereby the analytical performance criteria of liquid standards, single oxide solid standards and multi-element solid standards had to be determined. With the result that multi-element liquid standards can be used for calibration, very good agreement with the certified reference values and with the values obtained by ICP-OES was achieved in all cases. The precision of the method was better than 12% with an optimum sample mass of 0.2–0.4 mg. The results show that not only the major components in pure NMC compounds (e.g. starting materials) can be reliably analysed, but also the cathode coatings made from recycled battery materials. This demonstrates the range of applications of the methods and their suitability under industrial conditions, for example in the analysis of recyclates. The technology is almost predestined for use in industrial laboratories in order to quickly and accurately determine the stoichiometric composition of cathode coatings from aged lithium batteries and to ensure battery shredding by type.