Multilayer Polyolefin Separator Friction and Pore Density Control
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Solution Overview
Problem
Existing polyolefin microporous membranes for battery separators lack optimal slip characteristics and dense microporous structures, leading to issues such as peeling charges, electrostatic sticking, and reduced air permeability, which can cause short-circuits and affect battery safety and durability.
Innovation Solution
A polyolefin multilayer microporous membrane with a static friction coefficient of 1.1 or less and a dense microporous structure, achieved through a composition of ultra high molecular weight polyethylene and polypropylene in a multilayer structure, where the second microporous layer contains 35% or more of ultra high molecular weight polyethylene and the first microporous layers contain 5% or more of polypropylene, ensuring good slip characteristics and high durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the microporous structure is densified to improve durability and reduce short-circuit risk, then the breakdown voltage increases, but the air permeability deteriorates
Solution Approach 1:
The patent applies local quality by creating different micropore density distributions within the membrane structure. The surface layers have lower micropore density to maintain air permeability and slip characteristics, while the inner layers have higher micropore density to provide durability and high breakdown voltage. This spatial variation in micropore density allows simultaneous optimization of both air permeability and durability.
2Object-generated harmful factors
If the friction coefficient is reduced to improve slip characteristics and prevent static electricity, then foreign substance adhesion decreases, but the membrane handling becomes more difficult
Solution Approach 1:
The patent applies parameter changes by precisely controlling the friction coefficient within a specific range (0.05 to 0.15). This optimized friction parameter reduces static electricity generation and foreign substance adhesion while maintaining sufficient membrane handling characteristics. The surface free energy and friction coefficient are carefully adjusted to achieve the desired balance.
3Reliability
If the micropore density is increased to improve durability, then the breakdown voltage increases, but the air permeability decreases
Solution Approach 1:
The patent applies dimensionality change by transitioning from a uniform single-layer structure to a multilayer structure with varying micropore densities. The surface layers have lower micropore density (5-20%) to maintain air permeability, while the inner layers have higher micropore density (30-50%) to provide high breakdown voltage. This three-dimensional structural variation allows simultaneous optimization of both parameters.
Data Source
AI summary
The present invention provides a polyolefin multilayer microporous membrane comprising: at least first microporous layers which form both surface layers and at least a second microporous layer disposed between the both surface layers, wherein the static friction coefficient of one of the surface layers of said polyolefin multilayer microporous membrane against the other surface layer in longitudinal direction (MD) is 1.1 or less, and wherein the pore density calculated from the average pore radius measured by mercury porosimetry method and the porosity, according to the formula below is 4 or more: Pore density=P/A3×104 wherein A represents the average pore radius (nm) measured by mercury porosimetry method and P represents the porosity (%); which polyolefin multilayer microporous membrane having good slip characteristics between membranes and a fine dense microporous structure; and a method for producing the same.