Component materials of power lithium battery -Lithium - Ion Battery Equipment

Research on component material modeling of power lithium batteries -Lithium - Ion Battery Equipment

When it comes to driving, safety comes first. As the most eye-catching newcomer, electric vehicles urgently need to improve themselves in the field of safety. The development of battery pack mechanics simulation models plays a key role in the development of collision safety of future electric vehicles. Research on the mechanical behavior of the component materials of lithium batteries aims to establish a basis for refined battery pack models. This article will introduce to you the relevant research of this research group on lithium battery component materials.

First, when we disassemble the lithium battery cell, we will see the following scene: the internal cells of the lithium battery are stacked in the order of "electrode-separator-electrode", and the electrodes are placed on the current collector (the positive electrode is aluminum foil, the negative electrode is copper Foil) is obtained by coating active coatings on both sides. These components form a complete and usable lithium battery cell under the infiltration of electrolyte.

The mechanical properties of the metal current collector and coating of the electrode are significantly different, so the contributions of the two must be considered separately in refined modeling. It is not realistic to conduct mechanical tests on coating materials alone, so tensile tests at different loading rates were conducted on the positive and negative electrodes and the current collector after the coating was removed.

In order to intuitively show the influence of the coating on the electrode, the collector thickness and electrode thickness are unified as the collector thickness in the stress calculation. As can be seen from Figure 2, both the strain rate and the influence of the coating are concentrated on the plastic segment. The coating enhances the failure load of the collector under uniaxial tension to a certain extent; the process of removing the coating from the electrode may have a negative impact on the electrode. The film caused damage and reduced its failure strain, especially the positive electrode material; the anisotropy of the positive and negative electrodes was not obvious. In summary, the finite element simulation modeling of electrodes must take into account the strain rate effect of the electrode and the impact of the coating on the metal current collector. Compared with the tensile properties of electrode materials, the impact of coatings on the mechanical properties of electrode materials is more reflected in the impact on the compressive properties of electrode materials and battery cells. For detailed information, please pay attention to the relevant research of Luo Hailing of this research group.

Characterizing the mechanical behavior of the separator is the top priority in establishing a refined model. The rupture/failure of the separator is an important reason for triggering battery short circuit. Similarly, the diaphragm material was subjected to loading tests at different directions and different strain rates, and the surface of the diaphragm was microscanned. The test results are shown in Figure 3. The diaphragm material used in this study is a single-layer ceramic-coated diaphragm. Unlike electrode materials, separator materials exhibit significant anisotropy and strain rate effects covering the full strain range during the stretching process. In addition, the diaphragm materials in different directions show different fracture modes. Among them, the 0° direction shows irregular fractures, and the 45° and 90° specimens have straight fractures.(Lithium - Ion Battery Equipment)

The anisotropic behavior of the diaphragm and the different fracture modes start with the manufacturing process of the diaphragm. There are two main preparation processes for separators: dry method and wet method. Both processes are inseparable from the later unidirectional or biaxial stretching to orient the film to form or expand the micropores of the film, thereby realizing the "electron channel" of the separator inside the battery. "function. From the microscopic image of the separator, the internal micropores can be clearly seen. At the same time, it can be seen that the important fibers inside the separator show a certain orientation arrangement, and this orientation arrangement is an important reason for the significant anisotropy of the separator.

At this point, the different fracture forms of diaphragms in different directions have also been explained. Diaphragm fractures in the 0° direction have fractures of important internal fibers, while diaphragm fractures in the 45° and 90° directions are caused by the mutual separation of important fibers. The orientation of the fracture This is the orientation of the diaphragm fibers at breakage.



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