Cu-Coated Foil for Secondary Battery Negative Electrode Collectors
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Solution Overview
Problem
Existing foils for negative electrode collectors in secondary batteries face challenges in maintaining mechanical strength and conductivity when thinned to 20 µm or less, leading to plastic deformation and crack formation due to stress from lithium insertion and desorption in lithium-ion batteries.
Innovation Solution
A Cu-coated foil with a three-layer structure, comprising an iron-based alloy layer made of precipitation hardened stainless steel and Cu layers on both surfaces, is developed, with a thickness of 20 µm or less, and undergoes short-time aging treatment to enhance elastic limit and conductivity, reducing volume resistivity to 7 µΩ·cm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the foil thickness is reduced to 20 µm or less to increase battery capacity, then the battery capacity is improved, but the mechanical strength decreases leading to plastic deformation and crack formation
Solution Approach 1:
The patent employs a three-layer composite structure consisting of a nickel-based metal layer (providing mechanical strength) sandwiched between two copper layers (providing conductivity). This composite structure allows the foil to maintain both high mechanical strength and high electrical conductivity even at thickness of 20 µm or less, resolving the contradiction between reducing thickness for capacity and maintaining strength to prevent deformation and cracking.
2Quantity of substance
If the foil thickness is reduced to 20 µm or less to increase battery capacity, then the battery capacity is improved, but the foil undergoes plastic deformation due to stress from lithium insertion and desorption
Solution Approach 1:
The nickel-based metal layer in the three-layer composite structure provides superior mechanical strength and elasticity, enabling the thin foil (20 µm or less) to withstand repeated stress from lithium insertion and desorption without undergoing plastic deformation. The copper layers maintain conductivity while the nickel layer ensures structural stability during battery cycling.
3Strength
If nickel-based metal is used to improve mechanical strength, then the strength is improved, but the conductivity decreases
Solution Approach 1:
The three-layer composite structure strategically assigns functions to each material: the nickel-based metal layer (middle layer) provides mechanical strength, while the copper layers (outer layers) provide high electrical conductivity. This division of labor allows the foil to achieve both high strength and high conductivity simultaneously, resolving the contradiction between using nickel for strength and copper for conductivity.
4Quantity of substance
If the foil is thinned to 20 µm or less to increase battery capacity, then the battery capacity is improved, but wrinkle-like irregularities form on the foil surface
Solution Approach 1:
The nickel-based metal layer in the composite structure provides sufficient mechanical strength and rigidity to prevent the formation of wrinkle-like irregularities on the foil surface, even when the total thickness is reduced to 20 µm or less. This maintains surface flatness while enabling thin-film design for increased battery capacity.
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 solution provides a negative electrode collector foil with improved elastic limit and conductivity, preventing plastic deformation and crack formation, even under increased stress from lithium expansion and contraction, while maintaining high conductivity and mechanical strength.
Implementation Method 1
the precipitation hardened stainless steel can improve the elastic limit by forming fine precipitates due to aging treatment
Implementation Method 2
thereafter aging treatment is performed at a temperature of 500°C or higher and 650°C or lower for a holding time of 0.5 minutes or more and 3 minutes or less
Data Source
Figure 1~2
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AI summary
A foil (5b) for a negative electrode collector of a secondary battery includes a Cu-coated foil (50) including an iron-based alloy layer (51) made of precipitation hardened stainless steel, and a pair of Cu layers (52, 53) respectively disposed on opposite surfaces of the iron-based alloy layer and made of Cu or a Cu-based alloy. The negative electrode collector foil has a thickness of 20 µm or less and a volume resistivity of 7 µΩ·cm or less.