Dynamic failure and crash simulation of carbon fiber sheet moulding compound (CF-SMC)

Carbon fiber sheet moulding compounds (CF-SMC) are a promising class of materials with the potential to replace aluminium and steel in many structural automotive applications. In this paper, we investigate the use of CF-SMC materials for the realization of a lightweight battery case for electric cars. A limiting factor for a wider structural adoption of CF-SMC has been a difficulty in modelling its mechanical behaviour with a computational effective methodology. In this paper, a novel simulation methodology has been developed, with the aim of enabling the use of FE methods based on shell elements. This is practical for the car industry since they can retain a good fidelity and can also represent damage phenomena. A hybrid material modelling approach has been implemented using phenomenological and simulation-based principles. Data from computer tomography scans were used for micro mechanical simulations to determine stiffness and failure behaviour of the material. Data from static three-point bending tests were then used to determine crack energy values needed for the application of hashing damage criteria. The whole simulation methodology was then evaluated against data coming from both static and dynamic (crash) tests. The simulation results were in good accordance with the experimental data. Graphic abstract

The effect of using the metal tube on laser welding of the battery case and the tab for lithium-ion battery

Given the drawbacks of the conventional welding methods in joining the battery case and tab in the lithium-ion battery, the laser welding technique using the metal tube has been introduced for the weld. The metal tube is supposed to contribute a positive effect on protecting the outside structure by blocking the injection of the spatters. However, the use of the metal tube is believed to affect the intensity as well as the power distribution of the laser gaussian beam. Through the observation and analysis in this study, both advantages and disadvantages of the application of the metal tube on the weld have been clarified. The use of the metal tube prevents the ejection of the spatter to the outside of the welding zone, the gap between the battery case and tab in the weld is also minimized. Besides, the limitation of the intensity and the power energy distribution of the laser Gaussian beam has caused significant changes in the morphology, mechanical, and electrical properties of the weld.

The Effect of Using a Metal Tube on Laser Welding of the Battery Case and the Tab for Lithium-Ion Battery

Given the drawbacks of the conventional welding methods in joining the battery case and tab in the lithium-ion battery, the laser welding technique using the metal tube has been introduced for the weld. The metal tube is supposed to contribute a positive effect including protection to the outside structure by blocking the injection of the spatters, and minimization of the contact gap between the battery case and table. However, the use of the metal tube is believed to cause the plume trapped inside and affect the intensity distribution of the laser gaussian beam. Through the observation and analysis in this study, both advantages and disadvantages of the application of the metal tube on the weld have been analyzed. The use of the metal tube prevents the ejection of the spatter to the outside of the welding zone, as well as minimize the air gap between the battery case and tab in the lap joint weld is also minimized. On the other hand, the trapped plume inside the metal tube and the reduction of the energy of the laser beam have been considered to cause significant changes in the morphology, mechanical, and electrical properties of the weld.

The Characteristics of Laser Welding of a Thin Aluminum Tab and Steel Battery Case for Lithium-Ion Battery

During lithium-ion battery packing, joining between battery cases and tabs is challenging for manufacturers due to dissimilar materials of the battery case and the tab, as well as their thicknesses. Laser welding, which has proven to produce a good weld with high productivity and low electrical resistance, is introduced to weld these materials. The weld was conducted with nanosecond-pulsed fiber laser and the effect of laser powers on mechanical and electrical properties as well as microstructure of the joint is investigated. The weld bead at the low laser power exhibited several blowholes on the surface, while the formation of voids including centerline and root cavities was observed through the cross-section. Moreover, the phenomenon of upward penetration (UP) was observed in all laser powers and recoil pressure which was generated by metal evaporation was supposed to cause the formation of an upward flow of the lower material. A hardness test was performed on both horizontal and vertical directions through the fusion zone. Additionally, the increase of upward penetration (UP) resulted in higher strength and lower electrical resistance of the weld.

Study on Poor Welding of Anode Tab and Battery Case of 21700 Lithium Ion Battery

The 21700 battery is a standard battery used by Tesla vehicles in the United States. It has the advantages of high energy density ratio, high output, low cost and high safety factor. The demand for 21700 battery is gradually increasing on the market. In order to meet the needs of new energy vehicles, the 21700 battery uses copper tab as the anode, which can minimize the internal resistance and improve the charge and discharge efficiency. However, the material of the battery case is steel, and the melting point of the steel is 452°C higher than that of copper. It is difficult to solder firmly using the traditional resistance welding process. In this paper, using TRIZ theory, through the causal analysis, technical conflict, material-field, physical conflicts and other tools, the 21700 battery anode resistance welding problem is analyzed in detail, and based on the analysis results to propose solutions: punching out the pitting on the tab forming a projection welding; inserting metal tungsten in the copper welding head; changing the welding pin head from the platform to the curved surface; introducing nitrogen gas. Under the premise of constant material and no increase in cost, the problem of poor welding of the anode and the battery case can be effectively solved.