Battery Separator Protrusions Prevent Delamination
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Solution Overview
Problem
Conventional battery separators face challenges with delamination of modified porous layers during high-speed processing and assembly, compromising safety, especially with thinner polyolefin porous membranes, which require enhanced adhesion and peel strength to prevent peeling and ensure safety.
Innovation Solution
A battery separator comprising a polyolefin porous membrane with randomly distributed protrusions and a modified porous layer containing a fluorine-based resin and inorganic particles, where the inorganic particles constitute 40-80 wt.% of the total, providing excellent adhesion and resistance to peeling, even at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a thinner polyolefin porous membrane is used to increase battery capacity, then the area for electrode and separator increases, but the adhesion between the membrane and modified porous layer deteriorates, causing delamination during processing
Solution Approach 1:
The patent applies preliminary action by forming protrusions on the polyolefin porous membrane surface before laminating the modified porous layer. These protrusions are created through controlled cooling of the extruded membrane, which causes localized shrinkage and surface deformation. This preliminary structural modification enhances the mechanical interlocking capability, ensuring strong adhesion even when using thinner membranes to increase battery capacity.
Solution Approach 2:
The patent applies local quality by creating non-uniform surface features (protrusions) at specific locations on the membrane surface rather than modifying the entire surface uniformly. The protrusions are formed at a density of 1-10 per cm² with heights of 1-10 μm, providing localized anchoring points that enhance adhesion without compromising the overall thinness and area of the membrane.
2Strength
If the cooling rate is increased to form protrusions, then the adhesion improves, but the production speed decreases
Solution Approach 1:
The patent applies partial action by implementing cooling only at specific zones during the extrusion process rather than uniformly throughout. The cooling rollers are positioned to cool the membrane surface partially as it exits the extruder, allowing protrusions to form in the critical bonding areas while maintaining faster overall production speed. This selective cooling approach achieves sufficient adhesion without the severe production speed reduction that would result from complete slow cooling.
3Strength
If a modified porous layer is laminated to improve adhesion, then the electrode adhesion improves, but the modified porous layer peels off during high-speed processing
Solution Approach 1:
The patent applies composite materials by combining the polyolefin porous membrane with a modified porous layer containing fluorine-based resin and inorganic particles. This composite structure provides both the electrode adhesion benefits of the modified layer and the mechanical stability of the polyolefin base. The protrusions on the membrane surface enhance the interfacial bonding between these two materials, preventing peeling during high-speed processing while maintaining excellent electrode adhesion.
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 achieves a high 0° peel strength, ensuring minimal delamination during processing and assembly, while maintaining excellent electrode adhesion and air permeation resistance, thus enhancing the safety and performance of lithium-ion battery separators.
Implementation Method 1
a pore blocking effect, which blocks an electrical current to prevent an excessive temperature increase at a temperature of approximately 120 to 150°C at the time of an abnormal temperature increase in a battery
Implementation Method 2
fluorine-based resins, which exhibit good electrode adhesion
Implementation Method 3
a heat-resistant porous layer containing a self-crosslinking acrylic resin and a plate-like boehmite
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention provides a laminated porous membrane which has a very high peel strength between a polyolefin porous membrane and a modified porous layer and is suitable for high-speed processing, and a battery separator having excellent adhesion with electrodes. (Solution) A battery separator having at least a polyolefin porous membrane having protrusions made of a polyolefin interspersed randomly on one surface at a density of not less than 3 protrusions/cm2 and not greater than 200 protrusions/cm2, the protrusions satisfying 5 µm ≤ W ≤ 50 µm (W being a size of the protrusion) and 0.5 µm ≤ H (H being a height of the protrusion); and a modified porous layer containing a fluorine-based resin and inorganic particles laminated on a surface of the polyolefin porous membrane having the protrusions; a content of the inorganic particles relative to a total of the fluorine-based resin and the inorganic particles of the modified porous layer being not less than 40 wt.% and less than 80 wt.%.