Trace-Element Copper Foil for Crack-Resistant Li-Ion Current Collectors
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Solution Overview
Problem
Copper foils used in lithium ion secondary batteries often suffer from poor mechanical properties, such as relaxation, wrinkling, and cracking due to thermal expansion and contraction during charge-discharge cycles, which affect the reliability and lifetime of the battery.
Innovation Solution
A copper foil with controlled trace amounts of silver, titanium, and sulfur, along with a tensile strength of 45 kg/mm² to 85 kg/mm² and electrical conductivity of 80% IACS or more, is developed to enhance mechanical properties and resist thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper foil is used as negative current collector, then electrical conductivity is improved, but mechanical properties deteriorate causing relaxation and wrinkling
Solution Approach 1:
The patent changes the chemical composition parameters of copper foil by controlling trace elements (silver: 0.1-10 ppm, titanium: 0.1-5 ppm, sulfur: 0.1-20 ppm) to simultaneously improve electrical conductivity and mechanical strength, resolving the contradiction between these two properties
Solution Approach 2:
The patent creates a composite copper foil material containing multiple trace elements (silver, titanium, sulfur) embedded in the copper matrix, which provides both excellent electrical conductivity and enhanced mechanical properties including tensile strength of 20-50 kgf/mm²
2Quantity of substance
If copper foil is coated with active material, then battery energy density is improved, but wrinkle formation increases
Solution Approach 1:
The patent modifies the surface properties and mechanical parameters of copper foil through controlled trace element addition, achieving a surface that maintains flatness (reduced wrinkles) while supporting high energy density active material coatings
Solution Approach 2:
The patent performs preliminary strengthening of the copper foil substrate through controlled trace element incorporation before coating with active material, preventing wrinkle formation during subsequent coating and battery operation
3Duration of action of moving object
If copper foil undergoes thermal expansion and contraction, then battery charge-discharge cycles are enabled, but crack development occurs
Solution Approach 1:
The patent optimizes the compositional parameters of copper foil by controlling trace elements (particularly sulfur content at 0.1-20 ppm which forms strengthening phases) to enhance ductility and crack resistance, enabling the foil to withstand repeated thermal expansion and contraction during charge-discharge cycles
Solution Approach 2:
The patent incorporates trace elements that create strengthening phases and grain boundary modifications in advance, providing crack resistance and ductility before the foil undergoes thermal cycling, thereby preventing crack development during battery operation
Data Source
AI summary
A copper foil is provided, including 5 ppm to 25 ppm silver. 0.5 ppm to 8 ppm titanium, and 5 ppm to 85 ppm sulfur. Also provided are a current collector for a lithium ion secondary battery and a lithium ion secondary battery.