Microporous Separator Membrane Balancing Strength and Thinness
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Solution Overview
Problem
Existing microporous membranes struggle to achieve high strength and thin-film formation due to the trade-off between high molecular weight polyolefins, which increase viscosity and make thin membrane formation difficult, and low molecular weight polyolefins, which reduce strength.
Innovation Solution
A microporous membrane with a polyolefin as the primary component, characterized by specific melt tension and melt flow rate (MFR) properties, including a melt tension of 30 mN or less and MFR of 0.9 g/10 min or less, along with controlled molecular weight distribution and crystallinity, enables high strength and thin membrane formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polyolefin is used to increase strength, then strength is improved, but viscosity increases making thin membrane formation difficult
Solution Approach 1:
The patent applies parameter changes by precisely controlling the melt flow rate (MFR) to 0.9 g/10 min or less and melt tension to 30 mN or less at 230°C. These parameter adjustments enable the polyolefin to achieve both high strength and good thin membrane formability by optimizing the balance between molecular weight and melt properties.
Solution Approach 2:
The patent uses composite materials by combining polyolefin with specific additives including inorganic fillers (such as alumina, silica, or titania) and lubricants. This composite structure enhances the mechanical strength while the additives also influence the melt properties to improve thin membrane formation capability.
2Ease of manufacture
If melt flow rate (MFR) is increased to reduce viscosity for thin membrane formation, then ease of manufacture is improved, but strength is reduced
Solution Approach 1:
The patent resolves this contradiction by establishing an optimal parameter range where MFR is 0.9 g/10 min or less and melt tension is 30 mN or less at 230°C. This precise parameter control ensures that the polyolefin maintains sufficiently low viscosity for thin membrane formation while preserving high molecular weight characteristics that provide strength.
Solution Approach 2:
The patent applies dynamics by controlling the molecular weight distribution and incorporating additives that modify the melt behavior dynamically. The combination of high molecular weight polyolefin with specific inorganic fillers and lubricants creates a system that exhibits appropriate flow characteristics during processing while maintaining structural integrity in the final product.
Data Source
Figure 1
AI summary
The purpose of the present invention is to provide a separator which is for a power storage device, and which has high strength and can be thinned. The separator for a power storage device has a microporous membrane containing polyolefin as a main component, wherein the melt tension of the microporous membrane as measured at a temperature of 230°C is 30 mN or less, and the melt flow rate (MFR) of the microporous membrane as measured under a load of 2.16 kg and at a temperature of 230°C is 0.9 g/10 min or less.