Silver-Titanium Copper Foil for Wrinkle-Resistant Li-Ion Collectors
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Solution Overview
Problem
Copper foils used in lithium ion secondary batteries suffer from poor mechanical properties, leading to wrinkles, cracks, and reduced reliability due to thermal expansion and contraction during charge-discharge cycles, affecting their performance and lifetime.
Innovation Solution
A copper foil with controlled trace amounts of silver, titanium, and sulfur, along with specific crystal orientation and mechanical properties, enhances electrical conductivity and resistance to relaxation, reducing the tendency to develop wrinkles and cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper foil is used as negative current collector, then electrical conductivity is improved, but mechanical strength deteriorates causing relaxation and wrinkles
Solution Approach 1:
The patent changes the chemical composition parameters of copper foil by controlling trace elements (silver: 0.1-10 ppm, titanium: 0.1-10 ppm, sulfur: 0.1-100 ppm) and crystal orientation parameters (M(220) ratio: 1.05-3.08, M(111) ratio: 0.57-0.87) to simultaneously achieve good electrical conductivity and mechanical strength, resolving the contradiction between conductivity and mechanical strength
2Quantity of substance
If copper foil is coated with active material, then battery energy density is improved, but wrinkle formation increases due to poor mechanical properties
Solution Approach 1:
The patent changes physical parameters including surface roughness (Rz ≤ 2.5 μm) and mechanical strength through controlled composition and crystal structure, which prevents wrinkle formation during coating while maintaining high energy density capability
3Duration of action of stationary object
If copper foil withstands thermal expansion during charge-discharge cycles, then battery lifetime is improved, but crack development increases due to mechanical failure
Solution Approach 1:
The patent optimizes mechanical strength parameters through controlled trace element content and crystal orientation, enabling the copper foil to withstand thermal expansion and contraction during charge-discharge cycles without developing cracks, thus extending battery lifetime
Data Source
AI summary
Provided is a copper foil, including 2 ppm to 21 ppm silver, 0.5 ppm to 5.5 ppm titanium, and 2 ppm to 80 ppm sulfur, wherein an orientation index of (220) surface of the copper foil is from 2.05 to 3.08. Also provided are a current collector for a lithium ion secondary battery and a lithium ion secondary battery.