Analysis of Mechanical Properties of Li-Ion Battery Cells Under Breathing and Swelling Mechanisms for Various Boundary Conditions

The market for electric vehicles has been expanding considerably in recent years, and with it, the onboard components have technologically evolved. When it comes to new technologies, it is important to pay particular attention to safety, so that the vehicle and, above all, its passengers are protected. One of the main components is the battery, which in addition to determining many important vehicle characteristics such as acceleration, range and price is also one of the most dangerous parts of an electric vehicle because, under certain conditions, it can catch fire or explode. The battery undergoes constant volume changes during use, mainly for two reasons: breathing and swelling. Breathing occurs due to the movement of the lithium ions from one electrode to the other. Their arrangement causes the volume occupied to be greater when the battery is fully charged. The volume changes caused by breathing are reversible. Swelling, on the other hand, refers to an irreversible increase of the cell volume due to the ageing of the battery. The cells are normally constrained inside modules and therefore subjected to a certain pretension. Volume change results in the generation of stresses on the cell surface within the module. Stress has a negative effect on the life cycle of the battery and can even cause an internal short circuit that makes the battery unusable and can lead to thermal runaway or exploding. All these effects should be limited both to improve the performance of the electric vehicle but above all to increase the safety of the vehicle. The phenomenon is analysed through a series of experiments involving the evaluation of the volume increase of fresh and aged non-pretensioned cells and the distribution and intensity of surface pressure of fresh and aged pretensioned cells. The collected data is used to develop a finite element model (FEM) able to simulate the mechanical behaviour of the battery under breathing and swelling conditions. The model will then be able to predict the stresses acting on the cell over time and can then be used to develop a module able to homogenise the stresses acting on the cell and limit their negative effects.


The market for electric vehicles has been expanding considerably in recent years, and with it, the onboard components have technologically evolved. When it comes to new technologies, it is important to pay particular attention to safety, so that the vehicle and, above all, its passengers are protected. One of the main components is the battery, which in addition to determining many important vehicle characteristics such as acceleration, range and price is also one of the most dangerous parts of an electric vehicle because, under certain conditions, it can catch fire or explode. The battery undergoes constant volume changes during use, mainly for two reasons: breathing and swelling. Breathing occurs due to the movement of the lithium ions from one electrode to the other. Their arrangement causes the volume occupied to be greater when the battery is fully charged. The volume changes caused by breathing are reversible. Swelling, on the other hand, refers to an irreversible increase of the cell volume due to the ageing of the battery. The cells are normally constrained inside modules and therefore subjected to a certain pretension. Volume change results in the generation of stresses on the cell surface within the module. Stress has a negative effect on the life cycle of the battery and can even cause an internal short circuit that makes the battery unusable and can lead to thermal runaway or exploding. All these effects should be limited both to improve the performance of the electric vehicle but above all to increase the safety of the vehicle. The phenomenon is analysed through a series of experiments involving the evaluation of the volume increase of fresh and aged non-pretensioned cells and the distribution and intensity of surface pressure of fresh and aged pretensioned cells. The collected data is used to develop a finite element model (FEM) able to simulate the mechanical behaviour of the battery under breathing and swelling conditions. The model will then be able to predict the stresses acting on the cell over time and can then be used to develop a module able to homogenise the stresses acting on the cell and limit their negative effects.