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The rapid development of lithium-ion battery (LIB) technology and the usage of such energy storage systems in the automotive industry highlight the need for better understanding of the processes responsible for LIB degradation and their effect on the battery mechanical performance. Such knowledge could potentially help increase battery safety in the case of car accidents involving electric vehicles (EV). During operation, lithium-ion traction batteries in EV experience reduction of their initial capacity, which is usually a combined effect of material degradation of the internal components, formation of additional layers, consumption of the electrolyte and formation of gasses inside the cells. Little is known, however, on how ageing affects the mechanical properties of cells with increased product life. The outcome of this research provides crucial information regarding the influence of product life on the mechanical behaviour of lithium-ion cells. Commercially available prismatic NMC-graphite LIBs, implemented in a current EV, were subjected to two different ageing routines. These include cell cycling at elevated temperatures, as well as the application of high temperature gradients on the battery by variation of the ambient and cooling temperature during ageing. Swelling in the form of a bulge on both battery sides was observed for all cells after the ageing process. This effect was later accounted to the gas, generated inside the cells as a consequence of battery cycling. The investigated cells were subsequently compressed by a 158mm hemispherical impactor in thickness direction with a testing velocity of 1mm/s. Test results showed high reproducibility for both fresh and aged batteries. Higher deformation and force intensity values at the onset of cell failure, indicated as a drop in cell voltage, were evaluated for both types of aged cells. Also a more abrupt failure of aged batteries was seen during testing, which is a consequence of the pressure rise inside the cell casing due to gas formation. Mechanical test results can be explained based on the observed degradation effects. Cell thickness increase accounts for the observed shift in displacement values for aged cells. The effect of increased mechanical resistance can be ascribed mainly consumption of electrolyte, which introduces material changes to the internal battery components. Based on the mechanical test results, conducted in this research, aged cells can be classified as less critical in terms of safety.
|Publication status||Published - 2021|
|Event||Batteries Event 2021 - Lyon, France|
Duration: 18 Oct 2021 → 20 Oct 2021
|Conference||Batteries Event 2021|
|Period||18/10/21 → 20/10/21|
- Lithium ions batteries
- Mechanical properties
- Product lifecycle
- Mechanical loading
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21_FFG_SafeLIB - Safety Aspects of Lithium-Based Tractions Batteries Including the Qualification for Second Life Applications
1/04/21 → 31/03/25
Project: Research project