Negative Electrode Core Laminate Bonding Strength
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Solution Overview
Problem
Ultrasonic bonding of copper or copper alloy negative-electrode core laminates to copper or copper alloy current collectors often results in cracks due to differences in crystal grain sizes between the bonding and non-bonding regions, leading to lattice defects and reduced bonding strength.
Innovation Solution
The implementation of a solid-state bonding layer with finer crystal grains in the bonding region and a central layer with suppressed crystal grain transformation ensures consistent crystal grain state across the bonding and non-bonding regions, enhancing bonding strength and reducing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultrasonic bonding is used to bond copper or copper alloy core laminate to copper or copper alloy current collector, then bonding strength is improved, but cracks are formed between bonding region and non-bonding region due to crystal grain size differences
Solution Approach 1:
The patent applies parameter changes by controlling the crystal grain size of the copper or copper alloy core laminate. Specifically, the crystal grain size is maintained within a predetermined range (e.g., 5-20 μm) to ensure uniformity between bonding and non-bonding regions. This parameter control prevents the formation of cracks that would otherwise occur due to crystal grain size differences during ultrasonic bonding, while still achieving adequate bonding strength.
2Strength
If welding recesses are deepened to improve bonding strength, then bonding strength between wound electrode assembly and current collector is improved, but cracks are more likely to form between bonding and non-bonding regions
Solution Approach 1:
The patent controls the crystal grain size parameter of the core laminate to prevent crack formation even when welding recesses are deepened for improved bonding strength. By maintaining uniform crystal grain size within a predetermined range throughout the core laminate, the material can withstand the stress concentrations created by deep welding recesses without developing cracks at the boundaries between bonding and non-bonding regions.
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 effectively decreases the occurrence of cracks and improves bonding resistance, maintaining the continuity of the crystal grain state and ensuring strong and stable bonding between the core laminate and current collector.
Implementation Method 1
a region of the first 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 of an interface between layers of the first electrode core
Implementation Method 2
the first electrode core laminate is bonded to the first electrode current collector by ultrasonic bonding
Data Source
AI summary
A negative-electrode core laminate of a portion of a negative-electrode core on which no negative-electrode active material layer is formed is bonded to a negative-electrode current collector by ultrasonic bonding. A core recess is formed in a bonding region of the negative-electrode core laminate bonded to the negative-electrode current collector by ultrasonic bonding, a region of the negative-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 negative-electrode core, the central layer being disposed between the solid-state bonding layers formed on both faces of the negative-electrode core. The average grain size of metal crystal grains constituting the solid-state bonding layer is smaller than the average grain size of metal crystal grains constituting the central layer.