Multi-layer Polyolefin Separator Adhesion and Delamination
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Solution Overview
Problem
Current battery separators face challenges in achieving low shut-down temperature, high permeability, and strong adhesion with modified porous layers, especially when processed at high speeds, leading to potential delamination and safety concerns due to increased air permeation resistance and reduced strength.
Innovation Solution
A multi-layer polyolefin porous membrane with protrusions of specific size and density is developed, which maintains low air permeation resistance and high permeability, and is laminated with a modified porous layer to ensure strong adhesion and prevent delamination during high-speed processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a low-melting point ingredient is added to improve shut-down characteristics, then shut-down temperature is reduced, but air permeation resistance increases and membrane strength decreases
Solution Approach 1:
The patent uses a composite structure consisting of a polyolefin porous membrane layer and a heat-resistant porous layer. The polyolefin layer provides shut-down characteristics by melting at low temperature to close pores, while the heat-resistant porous layer (made of materials like polyimide, polyamideimide, or aramid) maintains membrane strength and structural integrity at high temperatures, preventing the weaknesses caused by adding low-melting point ingredients alone.
2Productivity
If the separator thickness is decreased to increase battery capacity, then area increases, but the membrane may deform and delaminate during processing
Solution Approach 1:
The thin polyolefin porous membrane (providing shut-down function) is laminated with a heat-resistant porous layer that acts as a structural support. This composite structure enables the use of thinner separators while maintaining dimensional stability and preventing delamination during high-speed processing, as the heat-resistant layer provides mechanical reinforcement without compromising ion permeability.
Solution Approach 2:
The separator is divided into two functional layers: a thin polyolefin porous membrane layer (for shut-down characteristics and ion permeability) and a heat-resistant porous layer (for mechanical strength and dimensional stability). This segmentation allows each layer to optimize its specific function while working together to solve the contradictions of thinness versus stability.
3Strength
If adhesion between modified porous layer and substrate is improved by resin permeation, then adhesion strength increases, but air permeation resistance increases significantly
Solution Approach 1:
The heat-resistant porous layer is designed with controlled porosity and pore structure that provides sufficient adhesion to the polyolefin porous membrane through localized resin permeation and interfacial bonding, while maintaining high air permeability. The layer's porous structure ensures that adhesion is achieved at the interface without significantly blocking the overall air and ion flow paths through the separator.
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 excellent permeability and shut-down characteristics with exceptional adhesion between the modified porous layers, preventing delamination even during high-speed transport and processing, thereby enhancing battery safety and productivity.
Implementation Method 1
the decrease in viscosity of the polyethylene that configures the membrane and the shrinkage of the membrane may lead to membrane puncture at a certain temperature. This phenomenon is not limited to polyethylene. Even if the other thermoplastic resin is used, this phenomenon cannot be avoided at the temperature equal to or above the melting point of the resin
Implementation Method 2
the membrane exhibits ion permeability due to electrolytic solution impregnation
Implementation Method 3
ion permeability due to electrolytic solution impregnation
Implementation Method 4
polyamideimide resin, polyimide resin, and polyamide resin, which have both good heat resistance
Data Source
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AI summary
Considering that battery separators will require further thinner materials and lower costs in the future, a battery separator of the present invention, in which multi-layer polyolefin porous membrane with exceptionally high peel strength against a modified porous layer, suitable for high-speed processing during slit process and battery assembly process, and suitable for laminating on a multi-layer modified porous layer, and a multi-layer modified porous layer are laminated, is provided.