Electrolytic Copper Foil Curl Control via Gradient Current Density
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Solution Overview
Problem
The generation of curls in electrolytic copper foils for lithium secondary batteries poses a manufacturing defect, requiring control of curl-inducing factors within specific ranges to prevent wrinkling and overlapping, which is challenging due to differences in stress and surface characteristics between shiny and matte surfaces.
Innovation Solution
The electrolytic copper foil is produced by adding gelatin and HEC to a copper sulfate solution, applying a gradient current density during electrodeposition, and forming anti-corrosion layers with controlled chrome deposition to minimize curl indicators, ensuring the copper foil's surface roughness, chrome-deposited amount, and glossiness differences fall within predetermined ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the copper foil is produced using conventional electrolytic plating, then the manufacturing process is simple, but curl generation occurs due to stress and surface characteristics differences between shiny and matte surfaces
Solution Approach 1:
The patent applies different current densities to different regions of the copper foil during electrodeposition. Specifically, a first current density is applied initially, then a second current density is applied subsequently, creating localized variations in surface characteristics that balance the stress differences between shiny and matte surfaces, thereby controlling curl while maintaining manufacturing simplicity
Solution Approach 2:
The patent changes the electrical parameters during the electrodeposition process by applying different current densities at different time stages. The current density is adjusted from a first value to a second value, which modifies the surface characteristics and stress distribution of the copper foil, effectively controlling curl generation without complicating the manufacturing process
2Productivity
If the current density is increased to improve plating speed, then productivity increases, but curl generation is exacerbated due to greater stress differences
Solution Approach 1:
The patent employs periodic variation of current density during the electrodeposition process. A first current density is applied for an initial period to establish the copper deposit, then a second current density is applied for a subsequent period to refine the surface characteristics. This periodic action allows high productivity while controlling curl by managing stress accumulation through staged current application
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 controls curl amounts to a standard level, preventing wrinkling and overlapping during battery manufacturing, ensuring the copper foil can be used as a negative electrode current collector without compromising adhesion or discharge capacity.
Implementation Method 1
applying a current with a current density of 10 ASD to 80 ASD to the electrolyte so that the original foil is electrodeposited on a drum
Implementation Method 2
immersing the original foil in an anti-corrosion solution including 0.5 to 1.5 g/L of chrome and 1.2 g/L of 2-dioxyribose at a liquid temperature of 20°C to 35°C for 0.5 to 2 seconds so as to form the anti-corrosion layers
Data Source
Figure 1~4
AI summary
Disclosed is an electrolytic copper foil for a lithium secondary battery, wherein a curl indicator C of the electrolytic copper foil, which is defined as 1.21ΔR+1.12ΔCr+0.01ΔG, is 0 or above and 4.0 or below, where ΔR corresponds to an absolute value of a difference between roughness measured on a first surface of the electrolytic copper foil for a lithium secondary battery and roughness measured on a second surface thereof, ΔCr corresponds to an absolute value of a difference between a chrome-deposited amount of an anti-corrosion layer formed on the first surface of the electrolytic copper foil for a lithium secondary battery and a chrome-deposited amount of an anti-corrosion layer formed on the second surface, and ΔG corresponds to an absolute value of a difference between glossiness measured on the first surface of the electrolytic copper foil for a lithium secondary battery and glossiness measured on the second surface.