Copper Foil Anti-Swelling via Surface Roughness Control
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Solution Overview
Problem
Copper foils used in lithium-ion secondary batteries are prone to swelling, sagging, and wrinkling due to rapid room temperature recrystallization, leading to mechanical stress and defects that hinder the coating of electrode active materials, resulting in higher failure rates during long-term use.
Innovation Solution
The development of copper foils with specific surface roughness and lightness values, ranging from 0.6 to 1.9 μm and 12 to 35 respectively, which slows down room temperature recrystallization, reducing elongation wrinkles and enhancing tensile strength, thereby improving handling and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If copper foil is made thinner to enable downsizing of lithium-ion batteries, then battery size is reduced, but the copper foil becomes more susceptible to swelling, sagging, and wrinkling defects
Solution Approach 1:
The invention changes the surface roughness parameter of the copper foil from conventional smooth (Rz < 0.5 μm) to controlled roughness (0.5 μm ≤ Rz ≤ 2.0 μm). This parameter change increases friction between the foil and guide rollers, preventing slip-and-pull mechanical stress that causes swelling and sagging in thin foils, thereby maintaining reliability while enabling downsizing.
2Shape
If the surface roughness of copper foil is reduced to improve smoothness, then surface quality is improved, but friction between the foil and guide rollers decreases making it more likely to slip and pull
Solution Approach 1:
The invention optimizes the surface roughness parameter to a specific range (0.5 μm ≤ Rz ≤ 2.0 μm) that balances two competing requirements: it provides enough friction to prevent slip-and-pull during handling while maintaining acceptable surface smoothness for electrode active material coating. This controlled parameter change resolves the contradiction between smoothness and handling stability.
3Strength
If copper foil tensile strength is maintained at very high levels immediately after manufacturing, then mechanical strength is improved, but room temperature recrystallization occurs too rapidly causing swelling and deformation
Solution Approach 1:
The invention changes the surface roughness parameter which indirectly affects the recrystallization behavior. The controlled roughness (0.5 μm ≤ Rz ≤ 2.0 μm) creates a surface structure that moderates the recrystallization process, allowing the copper foil to maintain high tensile strength while reducing the rate of room temperature recrystallization, thereby preventing swelling and deformation.
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 copper foils exhibit anti-swelling, anti-sag, and anti-wrinkle properties, ensuring smoother processing and better electrical performance during long-term use, reducing the incidence of defects and improving the stability of lithium-ion batteries.
Implementation Method 1
This drop in tensile strength is a result of room temperature recrystallization.
Implementation Method 2
detaching an electrodeposited copper foil from the cathode drum when a predetermined thickness is obtained
Data Source
AI summary
The present disclosure relates to a copper foil which exhibits surprising anti-deformation properties (e.g., it is resistant to swelling, sagging, and wrinkling). Typically, the copper foil has (a) a shiny side with a surface roughness (Rz) in the range of 0.6 to 1.9 μm; (b) a matte side with a surface roughness (Rz) in the range of 0.6 to 1.9 μm; and (c) a lightness L* value of the matte side, based on the L*a*b* color system, in the range of 12 to 35. The disclosure further relates to an anode comprising an anode active material on an anode current collector, wherein the anode current collector includes the above-mentioned copper foil. The anodes are used in, for example, lithium ion secondary batteries.