Microporous Battery Separator Balancing Strength and Thinness
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Solution Overview
Problem
Existing microporous membranes for lithium-ion batteries face challenges in achieving high strength while maintaining thin membrane formation, as high molecular weight polyolefins result in high viscosity during melting, making thin membrane formation difficult, and reducing viscosity leads to reduced strength.
Innovation Solution
A microporous membrane comprising a polyolefin as a primary component with specific melt tension and melt flow rate (MFR) characteristics, including a melt tension of 30 mN or less and an MFR of 0.9 g/10 min or less, along with a high pentad fraction and controlled molecular weight distribution, to balance strength and moldability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polyolefin is used to increase strength, then puncture strength is improved, but viscosity at melting 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/10min or less and melt tension to 30 mN or less at 230°C. These parameter optimizations enable the polyolefin to achieve both high strength and good moldability for thin membrane formation, resolving the contradiction between strength and ease of manufacture.
2Ease of manufacture
If viscosity at melting is reduced to improve thin membrane formation, then moldability is improved, but strength is reduced
Solution Approach 1:
The patent optimizes the MFR parameter to 0.9 g/10min or less and melt tension to 30 mN or less, creating a balanced parameter set that simultaneously achieves good moldability for thin membrane formation and maintains high puncture strength. This parameter optimization resolves the contradiction between ease of manufacture and strength.
Data Source
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.