Positive Current Collector With Graded Melting Layers for Tab Welding
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Solution Overview
Problem
The existing composite current collectors for secondary batteries are prone to defects such as cold solder joints at the weld between the composite current collector and the tab, leading to a high defect rate of welding, which affects the performance and reliability of the battery.
Innovation Solution
A positive current collector with a conductive layer having at least three sublayers with stepwise increasing melting points, made from a metal matrix such as aluminum alloy and doped with elements like silicon, is used to enhance bonding with the support layer and reduce adhesion issues during welding, ensuring stronger connections and improved consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a composite current collector with a sandwich structure of metal-insulating polymer-metal is used, then the performance of the secondary battery is enhanced, but defects such as cold solder joints occur at the weld between the composite current collector and the tab, leading to a high defect rate of welding
Solution Approach 1:
The conductive layer is divided into multiple sublayers (first sublayer, second sublayer, third sublayer) with different melting points. This segmentation allows each sublayer to perform specific functions: the first sublayer bonds with the support layer, the second sublayer prevents adhesion to the welding device, and the third sublayer bonds with the tab, thereby resolving the welding defects
Solution Approach 2:
Different sublayers of the conductive layer are assigned different local properties (different melting points). The first sublayer has a melting point close to the support layer for strong bonding, the second sublayer has a higher melting point to prevent adhesion to the welding device, and the third sublayer has appropriate properties for tab welding, thus eliminating cold solder joint defects
2Strength
If the conductive layer is compounded with the support layer by ultrasonic welding, then the bonding force between the conductive layer and the support layer increases, but delamination and peel-off may occur
Solution Approach 1:
The melting point parameter of the conductive layer is changed by creating sublayers with different melting points. The first sublayer's melting point is specifically matched to be close to the support layer's melting point, enabling strong bonding during ultrasonic welding without causing delamination or peel-off
3Manufacturing precision
If the melting point difference between sublayers is excessive, then poor welding occurs, but if the melting point is too low, then adhesion to the welding device increases
Solution Approach 1:
The second sublayer is specifically designed with a higher melting point than the first and third sublayers. This local quality difference ensures that the second sublayer does not adhere to the welding device while still allowing the first and third sublayers to weld properly, thus maintaining welding consistency without excessive adhesion
Solution Approach 2:
The second sublayer acts as an intermediary layer between the first and third sublayers. It mediates the welding process by preventing adhesion to the welding device while allowing the adjacent sublayers to bond properly, thus resolving the conflict between welding consistency and adhesion
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 effectively increases the bonding force between the conductive and support layers, reduces delamination, and improves the welding consistency, leading to a lower defect rate and enhanced mechanical durability of the current collector.
Implementation Method 1
in a process of compounding the conductive layer and the support layer, for example, by ultrasonic welding, the conductive layer and the sublayer penetrate each other more easily, and bond with each other more firmly after cooling down
Implementation Method 2
Melting points of the at least three sublayers rise stepwise in ascending order of distance from the support layer
Data Source
AI summary
A positive current collector, a secondary battery, and an electrical device are provided. In some embodiments, the positive current collector includes: a support layer; and a conductive layer located on at least one surface of the support layer, where the conductive layer includes a first metal portion configured to connect to a tab, where, along a thickness direction of the conductive layer, the first metal portion includes at least three sublayers, and melting points of the at least three sublayers rise stepwise in ascending order of distance from the support layer. In the embodiments of this application, the first metal portion includes at least three sublayers, and the melting points of the at least three sublayers rise stepwise in ascending order of distance from the support layer, thereby helping increase a bonding force between the conductive layer and the support layer and reducing the probability of peel-off and delamination between the layers.