Co-extruded Battery Separator Uniformity via Shear Rate Control
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Solution Overview
Problem
Commercialization of co-extruded, multi-layered battery separators is hindered by uniformity issues due to difficulties in simultaneously extruding dissimilar polymers through a narrow orifice die, resulting in non-uniform products.
Innovation Solution
A co-extruded, multi-layered battery separator with uniform thickness and enhanced properties is achieved by using an extrusion die with a specific shear rate and incorporating various additives to improve melt integrity, shutdown temperature, and other performance characteristics, while maintaining a microporous structure suitable for lithium ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If co-extrusion process is used to produce multi-layered battery separator, then the separator can have multiple layers with different properties, but the product exhibits non-uniform thickness and physical properties
Solution Approach 1:
The patent changes the geometric parameters of the extrusion die, specifically using a land area ratio (the ratio of the cross-sectional area of the die land to the cross-sectional area of the orifice) of 0.1 to 10. This parameter optimization ensures uniform shear rate distribution across the die, which directly addresses the non-uniformity problem while maintaining the multi-layered structure capability.
Solution Approach 2:
The patent applies different properties to different layers of the separator by using dissimilar polymers with specific glass transition temperatures and molecular weights for each layer. The extrusion die is designed with separate channels for each polymer, allowing local customization of layer properties while achieving global uniformity through the optimized land area ratio.
2Adaptability or versatility
If dissimilar polymers are simultaneously extruded through a narrow orifice die, then multi-layered separator can be produced, but uniformity issues arise
Solution Approach 1:
The patent optimizes the land area ratio parameter of the extrusion die to a specific range (0.1 to 10) to ensure uniform shear rate distribution. This parameter change allows dissimilar polymers to be simultaneously extruded without the uniformity problems that plague conventional narrow orifice dies, resolving the contradiction between multi-layered structure capability and product uniformity.
Solution Approach 2:
The patent uses a master batch system where a pre-mixed polymer composition serves as a template for consistent layer formation. This copying approach ensures that each layer maintains uniform properties throughout the extrusion process, enabling reliable simultaneous extrusion of dissimilar polymers with consistent results.
3Ease of manufacture
If conventional extrusion die is used, then co-extrusion can be attempted, but the product is non-uniform and commercially unviable
Solution Approach 1:
The patent transforms the conventional extrusion die design by changing the land area ratio to a specific range (0.1 to 10), which fundamentally improves product uniformity. This parameter change makes the co-extrusion process commercially viable by producing reliable, uniform separators that meet quality standards, directly addressing the reliability issue.
Solution Approach 2:
The patent discards the conventional narrow orifice die design that produces non-uniform products and recovers/adopts an optimized die design with controlled land area ratio. This design transition enables commercial viability by eliminating the uniformity defects that have previously prevented co-extruded separators from reaching the market.
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 ensures uniform physical properties and improved performance metrics such as puncture strength, Gurley values, and melt integrity, making the co-extruded separator commercially viable for lithium ion batteries and other battery systems.
Implementation Method 1
an extrusion die with a specific shear rate
Implementation Method 2
a co-extruded, microporous membrane
Data Source
AI summary
A battery separator comprises a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having: a uniform thickness defined by a standard deviation of <0.80 microns (μm); or an interply adhesion as defined by a peel strength >60 grams.