Trace-Element 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 the battery's performance and lifetime.
Innovation Solution
A copper foil with controlled trace amounts of silver, titanium, and sulfur, along with a tensile strength ranging from 45 kg/mm² to 85 kg/mm², and a surface roughness of 2.5 µm or less, enhances electrical conductivity and mechanical properties, preventing wrinkles and cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper foil is used as negative current collector, then electrical conductivity is good, but mechanical properties are poor leading to relaxation and wrinkles
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content of non-copper elements (silver: 5-25 ppm, titanium: 0.5-8 ppm, sulfur: 5-85 ppm) in the copper foil. This compositional parameter optimization enhances the mechanical strength and relaxation resistance while preserving electrical conductivity, directly resolving the contradiction between good electrical conductivity and poor mechanical properties.
Solution Approach 2:
The patent creates a composite material system by incorporating trace amounts of silver, titanium, and sulfur elements into the copper matrix. This multi-element composite approach synergistically improves mechanical properties (tensile strength ≥45 kg/mm², elongation 1-15%) while maintaining the inherent electrical conductivity of copper, effectively addressing the reliability-strength contradiction.
2Productivity
If copper foil is coated with active material, then battery energy density increases, but wrinkles develop reducing performance
Solution Approach 1:
The patent controls surface roughness parameters (Rz ≤2.5 μm) and compositional parameters to prevent wrinkle formation during active material coating. By optimizing these parameters, the copper foil maintains surface flatness and mechanical integrity under coating stress, enabling high energy density without sacrificing manufacturing precision.
3Duration of action of stationary object
If copper foil bears thermal expansion and contraction, then battery cycle stability improves, but cracks develop reducing lifetime
Solution Approach 1:
The patent optimizes compositional parameters (silver 5-25 ppm, titanium 0.5-8 ppm, sulfur 5-85 ppm) to enhance crack resistance during thermal cycling. This parameter optimization enables the copper foil to withstand repeated thermal expansion and contraction without crack formation, directly improving battery lifetime and cycle stability.
Solution Approach 2:
The multi-element composite copper foil (Cu-Ag-Ti-S) provides superior crack resistance compared to pure copper. The composite structure absorbs thermal stress more effectively, preventing crack initiation and propagation during charge-discharge cycles, thereby extending battery lifetime while maintaining structural integrity.
4Strength
If tensile strength is increased to prevent relaxation, then mechanical integrity improves, but electrical conductivity decreases
Solution Approach 1:
The patent achieves the optimal balance between tensile strength (≥45 kg/mm²) and electrical conductivity (≥80% IACS) by precisely controlling the concentrations of alloying elements. This parameter optimization ensures that strength enhancement does not compromise electrical performance, resolving the contradiction between mechanical integrity and electrical conductivity.
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.