Polypropylene Separator Structure for Permeability and Puncture Strength
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Solution Overview
Problem
Existing separators for power storage devices struggle to simultaneously achieve high permeability, puncture strength, and dielectric strength, which are crucial for ensuring high safety and performance in lithium-ion batteries.
Innovation Solution
A separator for power storage devices is designed with a microporous membrane structure comprising laminated layers of polypropylene, where each layer has specific molecular weight distribution, pore size, and thickness to enhance permeability, puncture strength, and dielectric strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the separator membrane is made thinner to achieve high permeability, then the permeability is improved, but the puncture strength and dielectric strength deteriorate
Solution Approach 1:
The separator is constructed as a composite material consisting of a microporous base layer and a microporous surface layer with different pore structures. The base layer provides mechanical strength while the surface layer optimizes permeability, allowing the membrane to be thin yet maintain both high permeability and puncture strength.
Solution Approach 2:
Different regions of the separator have different pore structures optimized for different functions. The base layer has a first pore structure suitable for mechanical integrity, while the surface layer has a second pore structure optimized for ion permeability. This local differentiation allows the thin membrane to achieve both high permeability and sufficient strength.
2Productivity
If the separator membrane is made thinner to achieve high permeability, then the permeability is improved, but the dielectric strength deteriorates
Solution Approach 1:
The composite structure with two distinct microporous layers allows the thin membrane to maintain high dielectric strength. The base layer provides dielectric barrier properties while the surface layer ensures high ion permeability, enabling the separator to be thin without compromising safety.
Solution Approach 2:
The separator employs local quality differentiation where the base layer is optimized for dielectric properties and the surface layer for permeability. This functional zoning allows the thin membrane to achieve high permeability while maintaining sufficient dielectric strength for safety.
3Productivity
If the pore size is increased to improve permeability, then the permeability is improved, but the mechanical strength deteriorates
Solution Approach 1:
The separator uses a composite structure where the base layer has smaller pores optimized for mechanical strength, and the surface layer has larger pores optimized for permeability. This composite approach allows the overall membrane to achieve high permeability without sacrificing mechanical strength.
Solution Approach 2:
Different pore sizes are applied locally to different layers: the base layer has smaller pores for mechanical integrity, while the surface layer has larger pores for ion transport. This local optimization enables the membrane to simultaneously achieve high permeability and maintain mechanical strength.
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 proposed separator achieves high permeability, puncture strength, and dielectric strength, ensuring improved safety and performance of lithium-ion batteries, particularly under high-temperature conditions.
Implementation Method 1
a microporous layer (A) containing polypropylene as a principal component and a microporous layer (B) containing polypropylene as a principal component are laminated
Implementation Method 2
an area-average major axis pore diameter of the microporous layer (A) calculated from the analysis of the SEM image of the MD-ND cross section of the microporous membrane is 100 nm or greater and 280 nm or less
Data Source
AI summary
The present invention provides a separator for power storage devices, the separator having a microporous membrane in which a microporous layer (A) containing a polypropylene as a main component and a microporous layer (B) containing a polypropylene as a main component are superposed upon each other, or alternatively, at least one of the microporous layer (A) and the microporous layer (B) is contained. With respect to this separator for power storage devices, the trunk height as calculated from the analysis of an SEM image of an MD-ND cross-section of the microporous membrane is 500 nm to 1,000 nm (inclusive).