Surface-Treated Copper Foil Adhesion Oxidation
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges with copper foils that are prone to oxidation, mechanical damage, and poor adhesion of active materials, leading to reduced capacity and lifespan, particularly with silicon-based anodes that experience expansion issues and detachment from the current collector.
Innovation Solution
Surface-treated copper foils with controlled roughness, peak density, and chromium content, combined with a nodule and anti-tarnish layer, provide enhanced adhesion and mechanical strength, improving the uniformity and durability of active material coatings during processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the copper foil is made thinner to reduce battery weight and size, then the weight and size of the battery are reduced, but the mechanical strength and resistance to damage during processing deteriorate
Solution Approach 1:
The copper foil is combined with a silicon oxide coating layer to form a composite structure. The silicon oxide layer is formed by oxidizing the copper foil surface, creating a composite material that maintains the electrical conductivity of copper while providing enhanced mechanical strength and stability to prevent foil breakage during processing.
2Object-affected harmful factors
If a chromium anti-tarnish coating is applied to protect the copper foil, then the resistance to oxidation is improved, but the resistivity of the electrode increases if too much chromium is used
Solution Approach 1:
The chromium content in the anti-tarnish coating is precisely controlled within a specific range (25-70 μg/dm²). This parameter optimization ensures sufficient oxidation protection while maintaining low electrical resistivity. The patent also controls the surface roughness (Rz: 1.2-4.6 μm) to balance protection and electrical performance.
Solution Approach 2:
The anti-tarnish coating is applied selectively to the copper foil surface with controlled chromium distribution. The coating provides localized protection where needed while maintaining the overall electrical conductivity of the current collector. The surface treatment creates different zones with optimized properties for both protection and conductivity.
3Strength
If the surface roughness is increased to improve adhesion of active material, then the adhesion strength is improved, but the uniformity of active material coating deteriorates
Solution Approach 1:
The surface roughness parameters are precisely controlled within optimal ranges (Rz: 1.2-4.6 μm, Spd: 490,000-1,080,000 mm⁻²). This parameter optimization creates sufficient surface area for adhesion while maintaining uniform coating distribution. The controlled peak density ensures consistent active material attachment without creating excessive roughness that would hinder coating uniformity.
4Quantity of substance
If silicon-based active material is used to increase capacity, then the energy capacity per gram is increased, but the adhesion to current collector and structural stability deteriorate due to 400% size change
Solution Approach 1:
The copper foil surface is pre-treated with a silicon oxide coating before applying the silicon-based active material. This preliminary surface modification creates a stable interface that accommodates the 400% volume change of silicon during lithium insertion/extraction. The oxidized surface layer prevents direct contact between silicon and copper, maintaining adhesion stability throughout charge/discharge cycles.
Solution Approach 2:
A composite structure is formed with the silicon oxide coating layer between the copper foil and silicon-based active material. This intermediate layer acts as a buffer that accommodates silicon's volume expansion while maintaining structural integrity and electrical conductivity, preventing foil breakage and capacity fading.
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 surface-treated copper foils exhibit improved adhesion to active materials, increased mechanical strength, and better resistance to oxidation, enabling higher capacity, longer cycle life, and reduced weight, thus enhancing the performance and longevity of lithium-ion secondary batteries.
Implementation Method 1
the copper foil is exposed to oxygen and can become oxidized
Implementation Method 2
the copper foil typically includes an anti-tarnish coating such as a chromium coating
Data Source
AI summary
Surface-treated copper foils including a copper foil having a first side and an opposite-facing second side and two treatment layers disposed on the first side and the second side respectively are described. Each treatment layer provides a treated surface which exhibit a ten-point average roughness Rz in a range of 1.2 μm to 4.6 μm and a peak density (Spd) in a range of 490,000 to 1,080,000 mm−2. Additionally, the Cr content in each of the treatment layers is a range of 25 to 70 μg/dm2. The surface-treated copper foils have excellent electrode active material coating properties, such as good adhesion and uniformity.