Electrolytic Copper Foil Grain Zoning for Strength and Elongation
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Solution Overview
Problem
Conventional electrolytic copper foils used as current collectors in secondary batteries face challenges in achieving the necessary tensile strength and elongation properties, which are critical for maintaining battery performance under severe charging and discharging conditions, and require additional surface treatments that complicate the manufacturing process and increase costs.
Innovation Solution
The electrolytic copper foil is designed with distinct average cross-sectional grain sizes in surface and center areas, where the surface area has smaller grains (G1) and the center area has larger grains (G2), with specific ratios and dimensions to achieve enhanced tensile strength and elongation, preventing cracking and tearing during battery operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrolytic copper foil is prepared by conventional electrodeposition process, then the manufacturing process is simple, but the elongation and tensile strength properties are insufficient for severe battery conditions
Solution Approach 1:
The patent applies local quality by creating distinct grain size zones within the copper foil cross-section. The surface area (within 2μm from surface) contains first grains with smaller average cross-sectional grain size (0.5-2.0μm) for high strength, while the center area contains second grains with larger average cross-sectional grain size (3-9μm) for high elongation. This spatial differentiation of grain sizes allows different regions to fulfill different mechanical requirements simultaneously, resolving the contradiction between strength and elongation without adding process complexity.
2Strength
If separate surface treatment is performed to improve physical properties, then the tensile strength and elongation are improved, but the manufacturing process becomes complex and costs increase
Solution Approach 1:
The patent merges the grain structure control and surface property improvement into a single electrodeposition process. By optimizing deposition parameters (current density, temperature, electrolyte composition) to create the desired bimodal grain size distribution directly during manufacturing, the need for separate post-deposition surface treatments is eliminated. This integration maintains manufacturing simplicity while achieving the required tensile strength and elongation properties.
Solution Approach 2:
The patent implements preliminary action by establishing the appropriate grain size distribution during the electrodeposition process itself, before any subsequent processing. The controlled formation of fine grains at the surface and coarse grains in the center occurs during the primary manufacturing step, pre-configuring the material properties needed for battery application without requiring later intervention or additional treatment steps.
3Strength
If the copper foil has high tensile strength, then it resists cracking, but the elongation may be reduced affecting bonding with active materials
Solution Approach 1:
The patent resolves this contradiction through local quality by assigning different grain size characteristics to different spatial regions. The surface area contains fine first grains providing high tensile strength and crack resistance, while the center area contains coarse second grains providing high elongation and ductility for bonding. This localized differentiation allows the foil to exhibit both high strength and good bonding capability simultaneously.
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 design ensures continuous quality reliability and excellent overall battery performance by maintaining high tensile strength and elongation, preventing cracking and tearing, and improving bonding with active materials, thus enhancing the discharge capacity retention rate.
Implementation Method 1
an electrolytic copper foil is prepared in a manner in which an aqueous solution of sulfuric acid-copper sulfate is used as an electrolyte, an electrodeposited copper is precipitated on a drum surface by applying a direct current between an anode (e.g., a positive electrode) and a rotating cathode drum (e.g., a negative electrode) immersed in the electrolyte
Data Source
Figure 1~2
Figure 3~4(b)
Figure 5~6
AI summary
The present invention relates to an electrolytic copper foil having an excellent elongation by adjusting an average cross-sectional grain size on at least one surface area of the electrolytic copper foil, with respect to a cross-section perpendicular to a longitudinal direction, and a ratio of the grain size, and to an electrode for a secondary battery and a secondary battery including the electrolytic copper foil.