Protective Copper Foil for Curl-Resistant Battery Electrodes
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Solution Overview
Problem
Copper foils used as anode current collectors in secondary batteries face issues such as curling, wrinkling, tearing, and surface degradation due to environmental exposure, which affect manufacturing and performance.
Innovation Solution
A copper foil with a protective layer and specific physical properties, including tensile strength, elongation, and surface retention rates, is manufactured using a controlled electrolytic process to prevent curling, wrinkling, and tearing, maintaining surface integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If copper foil thickness is reduced to increase battery capacity, then the amount of active materials that can be included increases, but curling occurs causing defects such as tears or wrinkles
Solution Approach 1:
The patent applies parameter changes by controlling the grain structure of the copper foil through specific manufacturing parameters (rolling reduction rate, annealing temperature and time). This creates a fine-grained structure that reduces curling while maintaining thin thickness, allowing increased active material loading without compromising foil integrity.
Solution Approach 2:
The patent creates a composite structure within the copper foil by forming a gradient grain structure with different grain sizes at different depths. The surface layer has finer grains to prevent curling, while the inner layer has coarser grains to maintain ductility, effectively combining the benefits of both structures.
2Productivity
If copper foil is made thinner to increase battery capacity, then more current collectors can be included, but manufacturing difficulty increases due to curling
Solution Approach 1:
The patent modifies manufacturing parameters including rolling reduction rate (40-70%), annealing temperature (150-250°C), and annealing time (5-30 minutes) to achieve a fine-grained structure that reduces curling. This makes thin copper foil manufacturing feasible without excessive curling defects.
Solution Approach 2:
The patent performs preliminary grain structure control during the manufacturing process itself, creating the fine-grained structure before the copper foil is used in battery assembly. This preliminary action prevents curling from occurring during subsequent handling and assembly operations.
3Ease of operation
If copper foil surface is exposed to external environment, then battery operation is enabled, but surface dissolution occurs reducing foil quality
Solution Approach 1:
The patent converts the harmful effect of environmental exposure into a beneficial controlled oxidation process. By pre-treating the copper foil surface to form a stable oxide layer, the naturally occurring dissolution is replaced with a stable, protective surface layer that actually protects the underlying copper from further degradation.
Solution Approach 2:
The patent performs preliminary surface treatment during manufacturing to form a stable oxide layer or apply protective coating before the copper foil is installed in the battery. This preliminary action prevents surface dissolution during battery operation and storage.
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 foil maintains structural integrity and surface state during manufacturing and environmental exposure, enhancing the productivity and performance of secondary batteries and related components.
Implementation Method 1
an electrolytic copper foil is widely used as an anode current collector
Implementation Method 2
the surface of the copper foil may be easily dissolved by an external environment
Data Source
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Figure 3
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AI summary
An embodiment of the present invention provides a copper foil that comprises: a copper layer containing more than 99.9 weight% copper, and a protective layer on the copper layer, and has a tensile strength index of 3.0 kgf/mm2 or less and an elongation index of 2.1% or less. The tensile strength index is calculated according to the following equation 1, [Equation 1] Tensile Strength Index = |Tensile Strength 2 - Tensile Strength 1|. In equation 1, tensile strength 1 is a tensile strength of a sample before the salt spray test, tensile strength 2 is a tensile strength of the sample after the salt spray test. The elongation index is calculated according to the following equation 2, Elongationindex=Elongation2−Elongation1. In equation 2, elongation 1 is an elongation rate of a sample before the salt spray test and elongation 2 is an elongation rate of the sample after the salt spray test. The salt spray test is conducted over 72 hours in 6 cycles with 5±1% NaCl, wherein 1 cycle consists of spraying for 2 hours at 35±2 °C followed by drying for 10 hours. An embodiment of the present invention provides a copper foil comprising 99.9 weight% or more of copper, with a first weight retention rate of 0.1% or less and a second weight retention rate of 0.3% or less. The first weight retention rate is calculated according to the following equation 3, [Equation 3] First Weight Retention Rate=|(Weight after 5 hr immersion-Weight before immersion)/Weight before immersion X 100|, and the second weight retention rate is calculated according to the following equation 4. [Equation 4] Second Weight Retention Rate=|(Weight after 24 hr immersion-Weight before immersion)/Weight before immersion X 100|.