Sub-regional differentiated safety factors design method for aircraft structure

The deformation and failure of the internal separator in a lithium-ion battery under external impacts is one of the crucial factors in triggering internal short circuits. The surfaces of battery electrodes are usually not smooth, which tends to cause stress concentration on the separator, affecting the mechanical stability of the battery. Therefore, based on numerical simulation and theoretical analysis, this study conducted an in-depth exploration of the mechanical behavior of the battery separator under the condition of being compressed on a non-smooth surface and its short-circuit safety boundaries. A representative unit cell, including a section of the separator with a width of 50 μm and the nearby cathode and anode coating areas, was selected for two-dimensional finite element modeling and numerical calculation. The study compares three forms of the surface morphology: (1) ideal plane; (2) densely packed granular surface; (3) single granular protrusion plane, to understand the effects of particle size, separator thickness, and loading rate. By analyzing the equivalent stress-strain curves of the separator, it was found that the separator under compression on a non-smooth surface exhibited a softening phenomenon compared with that under ideal flat surface compression. For the ideal plane case, the strain distribution is very uniform, so the load-bearing capacity of the battery is larger. However, for the cases of densely packed granular and single granular protrusion, under the same loading displacement, the loaded area is small, and the generated reaction force is also small. As the loading process proceeded, the gaps were gradually filled, the loaded area increased, and gradually tended to be loaded on the entire surface, and the load difference gradually decreased. Through the parametric analysis of the failure stress of the separator, it was discovered that with the increase in particle diameter, the decrease in separator thickness, or the increase in loading rate within a certain range, the separator exhibited softening behaviors such as a decrease in average stress and a backward shift of the yield point, and the short-circuit failure stress also decreased accordingly. Furthermore, by establishing an equivalent compressive constitutive model of the separator under compression on a non-smooth surface, the influence of roughness on the failure stress was theoretically explained, and the quantitative relationship between the two was deduced.