The increasing popularity of electric vehicles and the demand for efficient storage of energy from renewable sources has led to the recognition of lithium ion batteries (LiBs) as a potent solution. Therefore, the investigation of aging behaviour and safety risks is crucial.
In state-of-the-art LiBs graphite is used as negative electrode material and lithium metal oxides are mostly used as positive electrode material. A crucial aspect of LiBs is its safety and aging behaviour. One of the key ageing effects is the occurrence of lithium plating, which mainly takes place during charging at low temperatures, high C-rates, high states-of-charge (SOC) or due to manufacturing defects resulting in an acceleration of cell aging. In addition, transition metals (TMs) can deposit on the anode surface and act as a starting point for lithium plating, accelerating capacity fading. Lithium plating may result in either a reversible or an irreversible deposition of metallic lithium on the negative electrode surface. Lithium plating causes capacity fading due to irreversible reactions with the electrolyte and hence loss of active lithium. Additionally, dendrites can form from the plated lithium and puncture the separator resulting in a short circuit. This worst-case scenario can cause the cell to self-heat and ultimately lead to a thermal runaway. Therefore, investigating the aging behaviour of defective cells is of significant interest.

In the study presented on this poster, irreversibly deposited lithium and transition metal deposition on graphite electrodes in graphite||Li[Ni0.6Mn0.2Co0.2]O2 (NMC 622) one-layered pouch cells will be investigated. Therefore, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is used which provides spatially resolved information on the distribution of elements like lithium, transition metals (TMs) and phosphorous. LA-ICP-MS requires minimal sample preparation. To determine the safety risk of defective cells, three different defects are inserted in the pouch cell which simulate production errors and are compared to cells without a defect. The simulated defects are loss of active material (Line defect), the presence of a nonconductive object in the cell (Tape defect) and a separator fold. To analyse the influence of the introduced defect, the cells were aged for 100 cycles at 1 C (charge/discharge) with three 0.5 C cycles before and after aging to calculate the capacity loss. From the distribution of lithium and TMs, it is possible to draw conclusions regarding the safety risks associated with the inserted defects.