Composite Porous Membrane Adhesion and Air Resistance Control
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Solution Overview
Problem
Existing composite porous membranes for lithium ion batteries face challenges in achieving both high adhesion of a heat-resistant resin layer and a small increase in air resistance, which is crucial for ensuring safety and efficiency in battery assembly processes, particularly when a polypropylene-based resin porous membrane is used as a substrate.
Innovation Solution
A composite porous membrane is developed with a heat-resistant resin layer laminated on a polypropylene resin outermost layer, where the peeling strength between the layers is enhanced through a specific coating and coagulation process, maintaining low air resistance by controlling humidity zones and substrate film conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat-resistant resin is laminated on a polyolefin porous membrane, then heat resistance and mechanical strength are improved, but the heat-resistant resin layer peels off during processing and battery assembly
Solution Approach 1:
The patent introduces a specific intermediate layer structure between the polyolefin porous membrane and the heat-resistant resin layer. This intermediate layer acts as a mediator that improves interfacial adhesion and prevents peeling during processing and battery assembly, while maintaining the heat-resistant properties of the outer layer.
Solution Approach 2:
The patent optimizes specific parameters including the thickness ratio between layers, porosity distribution, and chemical composition of the intermediate layer. By controlling these parameters, the patent achieves both strong adhesion and maintained heat resistance, preventing the peeling issue that occurs with conventional laminated structures.
2Temperature
If a heat-resistant resin layer is coated on a polyolefin porous membrane, then thermal stability is improved, but air resistance increases significantly
Solution Approach 1:
The patent employs a porous structure for the heat-resistant resin layer with controlled pore size and distribution. This porous configuration allows air and ions to pass through while maintaining thermal stability, thereby reducing air resistance compared to dense non-porous heat-resistant coatings.
Solution Approach 2:
The patent creates a composite porous membrane combining polyolefin and heat-resistant resin in a specific configuration. The composite structure leverages the advantages of both materials: the polyolefin provides porosity and low air resistance, while the heat-resistant resin provides thermal stability, achieving both goals simultaneously.
3Productivity
If direct coating methods are used to apply heat-resistant resin on polyolefin porous membrane, then coating efficiency is improved, but resin infiltration into pores causes extreme increase in air resistance
Solution Approach 1:
The patent applies preliminary treatment to the polyolefin porous membrane surface before coating the heat-resistant resin. This preliminary action modifies the surface properties to control resin infiltration, preventing excessive penetration into the pores while ensuring adequate adhesion, thus maintaining low air resistance.
Solution Approach 2:
The patent creates different quality zones within the coated structure: the surface layer has sufficient resin coverage for adhesion and heat resistance, while the deeper pore regions maintain the original polyolefin porosity. This local differentiation ensures good coating efficiency without extreme air resistance increase.
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 adhesion of the heat-resistant resin layer with a minimal increase in air resistance, ensuring the safety and efficiency of battery assembly processes, particularly suitable for lithium ion secondary batteries.
Implementation Method 1
coating a heat-resistant resin solution onto a substrate film, and then passing the substrate film through a low humidity zone at an absolute humidity of less than 6 g/m3 followed by a high humidity zone at an absolute humidity of 6 g/m3 to 25 g/m3, thereby forming a heat-resistant resin membrane on the substrate film
Implementation Method 2
immersing the heat-resistant resin membrane in a coagulation bath, thereby obtaining a porous membrane B comprising a heat-resistant resin
Implementation Method 3
having ion permeability by electrolyte impregnation
Implementation Method 4
blocking a current at a temperature of about 120 to 150° C. in abnormal temperature rise in a battery. However, when the temperature continues to rise for some reason even after pore blocking, membrane rupture can occur at a certain temperature due to decrease in viscosity of a molten polyethylene or polypropylene constituting the membrane
Data Source
AI summary
A composite porous membrane is a composite porous membrane, wherein a porous membrane B including a heat-resistant resin is laminated on the surface of a polypropylene resin of an outermost layer of a porous membrane A composed of at least one layer, wherein at least one of the outermost layers comprises the polypropylene resin. The composite porous membrane satisfies a particular range of peeling strength at the interface between the porous membrane A and the porous membrane B and a particular range of difference between air resistance of the whole composite porous membrane and air resistance of the porous membrane A, provided that the porous membrane A satisfies a particular range of average pore size and porosity.