Development of a Material Model for Stress Calculations in Lithium-ion Batteries رسالة ماجستير

Abstract

All Solid state lithium-ion batteries are a promising source of energy for the newly de- veloped small devices due to their safety and high capacity. However, these kinds of batteries still experience a volume change in their composite cathode structure leading to magnificent deformations and high stresses that will cause a fatigue in their material structure. One of the solutions to overcome this problem is to add elastomers in specific amounts to the composite cathode material with small to no effect on the cathode conduc- tivity. In order to determine the best amount of elastomers, computer-based simulation is used to study the behaviour of the composite cathode after adding the elastomers. Pre- vious stress-strain results obtained from modeling the hyperelastic compressible material behaviour of elastomers using small strain theory are promising but inaccurate. In order to obtain more accurate hyperelastic material behaviour, we use the large strain theory to model the elastomers’ behaviour. We derive the equations required to represent the hyper- elastic behaviour of the material properties using large strain theory. We implement the derived equations in Fortran and use this implementation to integrate the new hyperelastic behaviour into ANSYS and GeoDict. Our initial results show more accurate stress-strain values which means that the new hyperelastic behaviour model has a potential to be im-

proved and used in future works.

All Solid state lithium-ion batteries are a promising source of energy for the newly de- veloped small devices due to their safety and high capacity. However, these kinds of batteries still experience a volume change in their composite cathode structure leading to magnificent deformations and high stresses that will cause a fatigue in their material structure. One of the solutions to overcome this problem is to add elastomers in specific amounts to the composite cathode material with small to no effect on the cathode conduc- tivity. In order to determine the best amount of elastomers, computer-based simulation is used to study the behaviour of the composite cathode after adding the elastomers. Pre- vious stress-strain results obtained from modeling the hyperelastic compressible material behaviour of elastomers using small strain theory are promising but inaccurate. In order to obtain more accurate hyperelastic material behaviour, we use the large strain theory to model the elastomers’ behaviour. We derive the equations required to represent the hyper- elastic behaviour of the material properties using large strain theory. We implement the derived equations in Fortran and use this implementation to integrate the new hyperelastic behaviour into ANSYS and GeoDict. Our initial results show more accurate stress-strain values which means that the new hyperelastic behaviour model has a potential to be im-

proved and used in future works.