Ultrasonic Welding Protrusion Stress Mitigation
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Solution Overview
Problem
The existing methods for joining a current collector to the protrusion portion of an electrode assembly in lithium-ion secondary battery cells often result in unfavorable conditions such as cracking or tearing, leading to conductivity issues and reduced durability and reliability due to stress concentration and abrupt thickness changes during ultrasonic welding.
Innovation Solution
The solution involves a metal material with a configuration where the central region is displaced towards the contact portion of the current collector, and the end regions are displaced away, allowing the protrusion portion to be interposed between the contact portion of the current collector and the metal material, which increases the thickness of the protrusion portion in one direction, thereby reducing stress concentration and preventing cracking or tearing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ultrasonic welding is conducted with the protrusion portion placed directly on the contact portion, then the joining process is simple, but the protrusion portion bends abruptly and cracks or breaks occur
Solution Approach 1:
A metal material is introduced as an intermediary component between the protrusion portion and the contact portion. This metal material has a thickness that gradually increases from one end to the other, serving as a transition element that distributes the pressurizing force during ultrasonic welding. The gradual thickness change prevents abrupt bending of the protrusion portion while maintaining effective joining, thus resolving the contradiction between manufacturing simplicity and structural integrity.
2Force
If a metal material with high rigidity and uniform thickness is used, then the protrusion portion is pressurized effectively, but stress concentration occurs at the end of the metal material causing cracking or tearing
Solution Approach 1:
The metal material is designed with non-uniform thickness, where the thickness gradually increases from one end to the other. This creates local variations in mechanical properties: the thinner end provides flexibility and reduces stress concentration, while the thicker end provides sufficient rigidity for effective pressurizing. This local quality variation allows the metal material to effectively transmit force while preventing cracking or tearing at critical locations.
3Device complexity
If the protrusion portion has abrupt thickness changes, then the electrode assembly structure is simple, but stress concentration occurs leading to cracking or breakage
Solution Approach 1:
The metal material's thickness parameter is varied gradually along its length, creating a smooth transition zone. This parameter change eliminates abrupt thickness changes in the overall assembly, distributing stress more evenly during welding and operation. The gradual thickness variation maintains structural simplicity while significantly improving the reliability and strength of the protrusion portion by preventing stress concentration points.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively mitigates stress concentration and prevents cracking or tearing during welding, ensuring a strong and reliable joint between the electrode foil and the current collector, enhancing the durability and reliability of the lithium-ion secondary battery cell.
Implementation Method 1
ultrasonic welding is conducted in state that a contact portion 3A of a current collector is placed on an anvil 30 which is a pedestal portion of a welding machine, the protrusion portion 8A is placed on the contact portion 3A, and a tip (or a horn) 31 of the welding machine is held in direct contact with the protrusion portion 8A
Data Source
AI summary
An electric storage device, including: an electrode assembly having at least one protrusion portion, the protrusion portion being formed of an end portion of any one of a positive electrode foil and a negative electrode foil and protruding in a laminated state from a side end of the other electrode foil of the both electrode foils; a current collector having a contact portion in contact with the protrusion portion; and a metal material that joins the protrusion portion by interposing the protrusion portion between the contact portion of the current collector and the metal material, wherein at least an end region in one direction along the opposing face is displaced in a direction away from the contact portion of the current collector than a central region of the opposing face is.