Polyester Film Current Collector for Thick Metal Deposition
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Solution Overview
Problem
Resin film current collectors suffer from thermal degradation and mechanical property degradation due to high-temperature vapor deposition processes, leading to wrinkles, folded ends, and adhesion failures, especially when thick metal layers are applied, resulting in short circuits and degraded battery performance.
Innovation Solution
A polyester film with specific resistivity and thickness, containing conductive particles like Ketjen black and carbon nanotubes, is used to support a metal layer, enhancing adhesion and mechanical strength, preventing thermal damage and improving stress resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vapor deposition processing is performed to form a thick metal layer on the resin film, then the electrical conductivity and current collecting capability are improved, but thermal damage occurs to the film surface resulting in degradation of mechanical properties
Solution Approach 1:
The patent introduces a cooling metal roll as an intermediary heat sink during vapor deposition. The resin film is brought into close contact with the cooling metal roll, which rapidly conducts heat away from the film surface, preventing thermal degradation while allowing thick metal layer formation
Solution Approach 2:
The patent applies high conveyance tension to the resin film during vapor deposition, changing the physical state of film contact with the cooling roll. This ensures intimate thermal contact and efficient heat removal, allowing the process to proceed without thermal damage despite high metal vapor temperatures
2Weight of moving object
If the resin film is made thinner to reduce battery weight, then the weight is reduced, but wrinkles and folded end parts occur during conveyance leading to poor adhesion and heat defeat
Solution Approach 1:
The patent applies high conveyance tension before and during the vapor deposition process to prevent wrinkles and folded end parts from forming. This preliminary action ensures the thin film remains smooth and properly adhered to the cooling roll throughout the deposition process
Solution Approach 2:
By controlling the conveyance tension parameter within an optimal range, the patent enables thin films to be processed without thermal damage. The high tension maintains film flatness and contact with the cooling roll, while the film thickness is kept within 1-30 μm to achieve weight reduction
3Reliability
If the conveyance tension is increased to prevent wrinkles and folded end parts, then adhesion to cooling roll is improved, but the film becomes more susceptible to breakage
Solution Approach 1:
The patent optimizes the conveyance tension parameter to a specific range that provides sufficient adhesion to the cooling roll while remaining below the film's breakage threshold. This balanced parameter setting resolves the contradiction between needing high tension for adhesion and avoiding excessive tension that causes breakage
Solution Approach 2:
The film undergoes discharge treatment before vapor deposition to improve its surface properties and adhesion characteristics. This preliminary action enhances the film's ability to adhere to the cooling roll at moderate tension levels, reducing the need for excessively high tension that would cause breakage
4Reliability
If the amount of power in discharge treatment is increased to improve charging efficiency, then adhesion is improved, but defects occur on the film surface due to sudden abnormal discharging
Solution Approach 1:
The patent applies discharge treatment with power within an optimal range - sufficient to improve adhesion and charging efficiency but not so excessive as to cause abnormal discharging and surface defects. This controlled partial action achieves the desired effect without the harmful consequences of over-treatment
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 film that resists thermal degradation and maintains mechanical integrity, ensuring excellent adhesion to cooling rolls and reducing defects, thereby improving the durability and performance of secondary batteries.
Implementation Method 1
the polyester film has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles
Implementation Method 2
apply high conveyance tension to the film to keep it in close contact with a cooling metal roll at a low temperature while performing vapor deposition processing
Implementation Method 3
a surface layer composed of a metal and/or metal compound provided on surfaces on both sides of a resin film as a base material by a vapor deposition processing such as vacuum deposition or vacuum sputtering
Data Source
AI summary
A problem to be solved by the present invention is to provide a film that is resistant to heat defeat when directly depositing a thick layer composed of a metal and/or metal-based compound, a current collector with excellent external stress resistance using the film, and a secondary battery with excellent pressure durability using the film. A solution to the problem is a secondary battery including a current collector having a layer (hereinafter referred to as layer M) composed of a metal and/or metal-based compound and having a thickness of 0.2 µm or more and 3.0 µm or less on surfaces on surfaces on both sides of a polyester film that satisfies the following (1) and (2): (1) a thickness of the polyester film is 1 µm or more and 30 µm or less; and (2) the polyester film has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles.