Heat-Treated Electrolytic Copper Foil for Lithium Battery Current Collectors
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Solution Overview
Problem
Current copper foils used in lithium batteries face challenges such as high manufacturing costs, difficulty in producing wide-width foils, contamination from lubricating oils affecting adhesion with active materials, and inadequate mechanical strength and elongation properties to handle volume changes and heat phenomena during charging and discharging.
Innovation Solution
A heat-treated electrolytic copper foil with specific resistivity of 1.68 to 1.72 µΩ·cm and grain mean diameter of 1.0 to 1.5 µm, exhibiting uniform tensile strength and high elongation percentage, is developed, featuring a single modal grain size distribution and controlled surface roughness to enhance adhesion and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rolled copper foil is used as current collector, then manufacturing cost is high and it is difficult to fabricate wide-width foil, but electrolytic copper foil may have insufficient mechanical strength and elongation properties
Solution Approach 1:
The patent applies parameter changes by controlling the grain size distribution (mean diameter 3-10 μm with specific D10-D90 ranges) and performing heat treatment at 100-300°C for 1-24 hours to achieve the optimal balance between mechanical strength and elongation properties in electrolytic copper foil
Solution Approach 2:
The patent creates a composite microstructure by combining copper foil with specific grain size distribution characteristics and controlled surface roughness (Rz 1.5-5.0 μm) to achieve both ease of manufacture and superior mechanical properties
2Reliability
If rolled copper foil is used, then adhesion with active material may be degraded due to lubricating oil contamination, but electrolytic copper foil needs to achieve excellent adhesion
Solution Approach 1:
The patent eliminates the harmful lubricating oil component from the manufacturing process by using electrolytic copper foil instead of rolled copper foil, thereby removing the source of contamination that degrades adhesion with active material
Solution Approach 2:
The patent optimizes the surface properties of the copper foil by controlling surface roughness (Rz 1.5-5.0 μm) and grain size distribution to enhance adhesion with active material locally at the interface, while maintaining overall foil quality
3Quantity of substance
If current collector thickness is increased to improve mechanical strength, then capacity per volume of lithium battery decreases, but thin copper foil may have insufficient strength to resist volume change and heating
Solution Approach 1:
The patent changes the microstructural parameters of the copper foil by controlling grain size distribution (mean diameter 3-10 μm) and performing heat treatment to achieve high strength-to-thickness ratio, enabling thin foil (6-15 μm) to possess sufficient mechanical strength
Solution Approach 2:
The patent creates a dynamic microstructure with specific grain size distribution that can adapt to volume changes during battery operation, allowing the thin foil to maintain structural integrity while accommodating electrode expansion and contraction
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 heat-treated copper foil provides improved mechanical strength, elongation properties, and adhesion with active materials, leading to enhanced performance and life characteristics of lithium batteries, including increased capacity and high-rate capability.
Implementation Method 1
heat treating for one hour at 200°C a copper foil manufactured through electrolysis
Implementation Method 2
a copper foil manufactured through electrolysis
Data Source
Figure 1
AI summary
Disclosed is an electrolytic copper foil obtained by heat treating a copper foil manufactured through electrolysis, the electrolytic coper foil having specific resistivity of 1.68 to 1,72µΩ · cm and a grain mean diameter of a crystallite of 1.0 to 1.5 µm.