Ultrasonic Bonding of Secondary Battery Positive Electrode Core
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Solution Overview
Problem
Ultrasonic bonding of aluminum or aluminum alloy positive-electrode core laminates to current collectors often results in cracks due to differences in crystal grain states between the bonding and non-bonding regions, leading to lattice defects and reduced bonding strength.
Innovation Solution
Controlled ultrasonic bonding conditions form a solid-state bonding layer with finer crystal grains in the bonding region and a central layer within the positive-electrode core, maintaining the crystal grain state continuity between regions, thereby reducing cracking and enhancing bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultrasonic bonding is applied to bond aluminum or aluminum alloy core laminate to current collector, then bonding strength is improved, but cracks are formed between bonding region and non-bonding region
Solution Approach 1:
The patent applies local quality by creating a bonding region with different crystal grain characteristics than the non-bonding region. The bonding region undergoes ultrasonic bonding that transforms the crystal grain structure, while the non-bonding region maintains its original state. This localized transformation allows strong bonding at the interface while managing stress distribution to reduce crack formation.
Solution Approach 2:
The patent utilizes parameter changes in the crystal grain state during ultrasonic bonding. The bonding process transforms the crystal grain structure in the bonding region, creating a gradient in material properties. By controlling the bonding parameters (ultrasonic frequency, amplitude, pressure, time), the patent optimizes the crystal grain transformation to achieve strong bonding while minimizing crack formation.
2Strength
If the number of welding recesses on core laminate is decreased to improve bonding strength, then bonding strength is enhanced, but stress concentration increases leading to cracks
Solution Approach 1:
The patent applies local quality by creating specific welding recess patterns with varying depths and distributions. Rather than uniform recesses, the design creates localized variations in the bonding interface that distribute stress more evenly while maintaining strong bonding in critical areas. This selective modification of the bonding interface geometry reduces stress concentration points.
Solution Approach 2:
The patent applies preliminary action by pre-forming welding recesses in the core laminate before the ultrasonic bonding process. These recesses are strategically designed to control the bonding interface geometry, allowing the bonding process to proceed more uniformly and reducing the likelihood of crack formation during and after bonding.
3Strength
If welding recesses are deepened to improve bonding strength, then bonding strength is enhanced, but crystal grain transformation increases causing cracks
Solution Approach 1:
The patent applies local quality by creating welding recesses with controlled depths and distributions that localize the crystal grain transformation to specific regions. This selective transformation maintains crystal grain state continuity in the non-bonding regions while achieving adequate bonding strength in the bonding regions through the modified geometry.
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 approach ensures strong bonding and reduced resistance between the positive-electrode core laminate and current collector, minimizing the occurrence of cracks and maintaining the crystal grain state continuity, thus improving the structural integrity of the secondary battery.
Implementation Method 1
the first electrode core laminate is bonded to the first electrode current collector by ultrasonic bonding
Implementation Method 2
a solid-state bonding layer with finer crystal grains in the bonding region and a central layer within the positive-electrode core, maintaining the crystal grain state continuity between regions
Data Source
AI summary
A positive-electrode core laminate of a portion of a positive-electrode core on which no positive-electrode active material layer is formed is bonded to a positive-electrode current collector by ultrasonic bonding. A core recess is formed in a bonding region of the positive-electrode core laminate bonded to the positive-electrode current collector by ultrasonic bonding, a region of the positive-electrode core laminate in which the core recess is formed includes a solid-state bonding layer and a central layer, the solid-state bonding layer being formed by solid-state bonding between layers of the positive-electrode core, the central layer being disposed between the solid-state bonding layers formed on both faces of the positive-electrode core, and the first average grain size of metal crystal grains constituting the solid-state bonding layer is smaller than the second average grain size of metal crystal grains constituting the central layer.