Electrolytic Copper Foil Current Collector for Lithium-Ion Battery
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Solution Overview
Problem
Lithium-ion secondary batteries using silicon or other active materials face issues with charge-discharge cycle efficiency due to swelling and contraction of the active material layer, leading to creasing and breakage of the current collector, which results in reduced battery performance and stability over time.
Innovation Solution
An electrolytic copper foil with a surface roughness of 0.8 to 2.8 µm and a 0.2% proof stress of 250 N/mm² or more after heat treatment between 200°C to 400°C, combined with stain-proofing or roughening, is used as the current collector to prevent deformation and breakage during charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon or other active materials are used to increase battery capacity, then the battery capacity increases, but the active material layer swells and contracts during charging and discharging, causing creasing and breakage of the current collector
Solution Approach 1:
The patent applies parameter changes by controlling the surface roughness of the copper foil current collector within a specific range (Ra: 0.5-3.0 μm, Rz: 2.0-5.0 μm) and optimizing the copper foil thickness (6-15 μm). These parameter adjustments allow the current collector to accommodate the swelling and contraction of silicon-based active materials during charge-discharge cycles, preventing creasing and breakage while maintaining structural integrity and electrical conductivity.
2Productivity
If the surface roughness of the copper foil is reduced to improve charge-discharge efficiency, then the charge-discharge efficiency improves, but the adhesion between the active material layer and current collector may be compromised
Solution Approach 1:
The patent optimizes the surface roughness parameters within specific ranges (Ra: 0.5-3.0 μm, Rz: 2.0-5.0 μm) to balance two competing requirements: maintaining sufficient adhesion between the active material layer and current collector while ensuring good charge-discharge efficiency. This controlled roughness provides mechanical interlocking for adhesion while not being so rough as to impede ionic transport and electron transfer.
3Weight of moving object
If the copper foil thickness is reduced to decrease battery weight, then the battery weight decreases, but the mechanical strength and resistance to deformation during swelling/contraction cycles is reduced
Solution Approach 1:
The patent optimizes the copper foil thickness within a specific range (6-15 μm) to achieve the lightest possible battery weight while maintaining sufficient mechanical strength. This controlled thickness provides adequate structural support to resist deformation during active material swelling and contraction, preventing current collector breakage and ensuring long-term battery reliability.
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 solution enhances the charge-discharge cycle efficiency and maintains the stability of the lithium-ion secondary battery by preventing creasing and breakage of the current collector, ensuring long-term performance and preventing short-circuits between electrodes.
Implementation Method 1
unprocessed copper foil that has been produced by electrolysis
Implementation Method 2
after heat treatment between 200°C to 400°C
Data Source
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AI summary
To provide an electrolytic copper foil for a negative electrode for a lithium-ion secondary battery with which it is possible to produce a long-life lithium-ion secondary battery in which there is no decline in the capacity retention ratio even when the charge-discharge cycling is repeated, that has long life, and no deformation of a negative electrode current collector occurs. The electrolytic copper foil constituting the negative electrode current collector for the lithium-ion secondary battery has, after heat treatment at from 200 to 400°C, a 0.2% proof stress of 250N/mm2 or more, and elongation of 2.5% or more; and the surface on which an active material layer of the electrolytic copper foil is provided has been rust-proofed, or roughened and rust-proofed. As a result of analysis of the depth profile (depth direction) obtained by performing secondary ion mass spectrometry (SIMS) in the thickness direction of the copper foil, the copper foil including: chlorine (Cl), carbon (C), and oxygen (O) each in a concentration of 1017 to 5×1020 atoms/cm3, and sulfur (S) and nitrogen (N) each in a concentration of 1015 to 1019 atoms/cm3.