Pouch Cell Electrode Foil Welding to Prevent Tab-Side Cracking
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Solution Overview
Problem
Vehicle battery electrode foils face stress issues during manufacturing and service, particularly under tension, which can lead to fractures and cracking, especially when multiple layers are welded together and subjected to various tests and operational conditions.
Innovation Solution
The method involves subdividing foil extensions into groups and performing ultrasonic welding along edges or over areas to create strong composite groups, followed by laser welding to a lead tab, and introducing wrinkle patterns to reduce stress and prevent cracking, while also using clamps to curl and relax the lead tab after welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple electrode foils are welded together to form a stack, then the battery capacity and power output are improved, but the stress concentration and risk of fracture increase
Solution Approach 1:
The foil extensions are divided into multiple groups (first group, second group, third group) that are welded separately and then connected together. This segmentation distributes the welding stresses across multiple smaller weld zones rather than one large weld, reducing stress concentration on individual foils while maintaining the electrical connectivity of the stacked battery structure.
Solution Approach 2:
The method performs preliminary ultrasonic welding of foil extensions to the lead tab before final assembly and testing. By pre-welding the foil extensions in a controlled manner with multiple groups connected sequentially, the structure is prepared to better withstand subsequent manufacturing stresses and operational loads, preventing fractures that might occur with single-step welding.
2Ease of manufacture
If foil extensions are welded directly to the lead tab, then the electrical connection is simplified, but stress differentiation and cracking risk increase
Solution Approach 1:
Instead of welding all foil extensions directly to the lead tab in a single operation, the invention segments the welding into multiple groups (first group welded first, then second group, then third group). This segmented approach allows each weld group to be optimized independently and distributes the mechanical stress more evenly across the connection interface, reducing stress differentiation and cracking risk while maintaining manufacturing efficiency.
3Strength
If ultrasonic welding is performed on foil extensions, then the connection strength is improved, but stress concentration at weld zones increases
Solution Approach 1:
The ultrasonic welding process is applied segmentally to different groups of foil extensions rather than all extensions simultaneously. The first group is welded first, then the second group, then the third group. This segmentation distributes the thermal and mechanical stress of ultrasonic welding across multiple separated zones, preventing excessive stress concentration at any single weld location while maintaining strong connections.
Solution Approach 2:
The foil extensions are pre-positioned and pre-aligned before ultrasonic welding is applied. This preliminary preparation ensures that when ultrasonic welding occurs, the stress is distributed more evenly across the weld zone rather than concentrating at misaligned points, maintaining connection strength while reducing peak stress values that could lead to cracking.
4Manufacturing precision
If the lead tab is rigidly fixed during welding, then the welding precision is improved, but the foil extensions are more susceptible to cracking under subsequent loads
Solution Approach 1:
The lead tab and foil extensions are pre-positioned and pre-clamped in the correct alignment before welding begins. This preliminary positioning ensures high welding precision while allowing the clamps to be removed after welding, providing stress relief and preventing the rigid constraint that would otherwise make the foil extensions susceptible to cracking under operational loads.
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 approach reduces stress differentiation among foils, inhibits cracking, and enhances the resistance of foil extensions against out-of-plane loads and bending, ensuring the battery's reliability and performance during service and testing.
Implementation Method 1
performing a first ultrasonic weld on a first group of foil extensions to define a first foil extension weld portion, and performing a second ultrasonic weld on a second group of foil extensions to define a second foil extension weld portion
Implementation Method 2
the first group of foil extensions and the second group of foil extensions are connected to the lead tab via a laser weld
Data Source
AI summary
A vehicle battery includes a pouch cell configured to provide power to at least one power system of a vehicle, and multiple electrode foils stacked together at least partially within the pouch cell. Each of the multiple electrode foils includes a foil extension at an end of the electrode foil, a first group of foil extensions are connected together via a first ultrasonic weld to define a first foil extension weld portion, and a second group of foil extensions are connected together via a second ultrasonic weld to define a second foil extension weld portion.