Deciphering the lithium ion movement in lithium ion batteries: determination of the isotopic abundances of 6 Li and 7 Li.

Lithium ion batteries (LIBs) are the energy storage technology of choice in the context of renewable energies and electro-mobility. It is imperative to get a thorough understanding of the aging mechanisms to achieve a prolonged cycle and calendar life. One major drawback of the technology is continuous capacity fading during operation, which is partly attributed to the loss of active lithium, the object of this work's analysis. While lithium ion battery aging is an intensively researched topic, there is still the need to determine the origin of the lost lithium and the lithium migration into the different cell components over time. To achieve this goal, different plasma-based mass spectrometric techniques in combination with isotope analysis are applied to obtain bulk as well as depth-resolved information about lithium ion movement and distribution of lithium in aged LIB cells. Different aging experiments are performed on NCM622/graphite cells with a 6 Li-enriched electrolyte with subsequent Li analysis of the cell components. The results show that the charging rate, as well as the cycle number, has an impact on the 6 Li/ 7 Li-abundances and that the overall abundances show a rapid mixing of the isotopic species already after the first charge/discharge cycle for all cell components.