Embossed Foil Stack Welding for Zero-Gap Battery Tabs
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Solution Overview
Problem
Existing methods for connecting metal foils in lithium-ion battery cells, such as ultrasonic welding and laser beam welding, result in unreliable and low-strength connections due to air pockets and cavities, leading to reduced electrical conductivity and robustness.
Innovation Solution
An ultrasonic welding device with a sonotrode and anvil that forms a defined embossing surface by compacting the metal foils, which is then used to guide a laser beam for welding, ensuring a zero gap and homogeneous conditions for laser beam welding, thereby preventing cavity formation and enhancing connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ultrasonic welding is used to connect metal foils, then the connection is easier to manufacture, but the connection reliability is low and connections become loose over time
Solution Approach 1:
The patent applies preliminary action by first compacting the metal foils using an ultrasonic welding device with extensions to create a defined surface, and then performing laser beam welding on this pre-prepared surface. This two-step process ensures that the foils are properly positioned and compacted before the final welding, preventing connection loosening over time while maintaining ease of manufacture.
2Strength
If laser beam welding is used to weld metal foils, then the connection strength is improved, but air pockets and cavities form between the metal foils reducing electrical conductivity
Solution Approach 1:
The patent eliminates air pockets and cavities by first compacting the metal foils using the ultrasonic welding device with extensions that create a defined surface. This preliminary compaction removes air gaps between foils, ensuring complete contact before laser beam welding is applied, thus achieving strong connections without harmful air pockets that would reduce electrical conductivity.
Solution Approach 2:
The extensions on the ultrasonic welding device act as an intermediary between the ultrasonic welding tool and the metal foils. These extensions create a defined surface that ensures proper foil positioning and contact, mediating the transition from ultrasonic compaction to laser welding and preventing cavity formation during the process.
3Force
If the sonotrode and anvil have a roughened surface for compaction, then the compaction is improved, but the laser beam may impact outside the compacted area resulting in unreliable bonds
Solution Approach 1:
The patent applies local quality by providing that the extensions on the sonotrode or anvil have a defined surface (smooth or controlled roughness) specifically in the area that contacts the metal foils during compaction. This localized surface definition ensures that the compacted area has precise boundaries, allowing the laser beam to accurately target only the intended compacted region and preventing impacts outside the compacted area.
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
The solution provides a reliable and robust connection between metal foils and the cell conductor, ensuring consistent penetration depth and reducing the risk of air pockets, resulting in improved electrical conductivity and durability of the metal foil stack.
Implementation Method 1
The cathodes and anodes are typically formed by metal foils... The anode and cathode tabs are ultrasonically welded together... DE 10 2012 018 912 A1 discloses a method for producing a foil stack, in which the metal foils to be joined are first pre-fixed and compacted using an ultrasonic welding device
Implementation Method 2
the metal foils, with or without the cell conductor, are welded together using a laser beam... followed by a second ultrasonic welding process, in which a reinforcement plate is joined to the tab. A connecting element is then laser-welded to the reinforcement plate
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3d
AI summary
The invention relates to an ultrasonic welding device (2) for introducing an embossed surface (16) into a metal foil stack (14) for a cell of a lithium-ion battery, comprising a sonotrode (4) and an anvil (6), wherein the anvil (6) or the sonotrode (4) has a number of first protrusions (8) projecting from the working surface (4c and 6a) of the sonotrode and the anvil, respectively, in order to form the embossed surface (16), in particular the web-like embossed surface, by compacting the metal foil stack (14). The invention additionally relates to a method for producing a metal foil stack (14) of metal foils (12) for a cell of a lithium-ion battery, in particular using such an ultrasonic welding device (2).