Polyethylene Microporous Membrane with Low Thermal Shrinkage
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Solution Overview
Problem
Conventional polyethylene microporous membranes used as separators in secondary batteries face a trade-off between high permeability and heat resistance, limiting their application in high-capacity and high-output batteries due to inverse relationships between these properties.
Innovation Solution
A polyethylene microporous membrane with improved heat resistance and high gas permeability is manufactured through a sequential biaxial stretching process, including diluent extraction before transverse stretching and specific heat treatment, achieving a PS index of 110 or more, with a thickness of 3 μm to 30 μm, puncture strength of 0.15 N/μm or more, and shrinkage rate of 5% or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional separator implements high permeability to improve capacity and output, then gas permeability is improved, but heat resistance deteriorates due to the inverse relationship between permeability and heat resistance
Solution Approach 1:
The patent changes the physical and chemical parameters of the polyethylene microporous membrane, specifically controlling porosity at 40-50%, pore diameter at 0.5-2.0 μm, and implementing a multi-step heat treatment process at different temperatures (first heat treatment at 80-100°C, second heat treatment at 100-120°C) to simultaneously achieve high gas permeability and improved heat resistance
Solution Approach 2:
The patent creates a composite structure by combining polyethylene base material with a controlled microporous network structure, where the specific pore distribution and size arrangement enable both high ion permeability for battery performance and thermal stability for safety
2Strength
If a microporous membrane has large pore diameter to achieve excellent electrical properties and strength, then puncture strength is improved, but porosity is limited to 40-50% which does not meet high-capacity battery requirements
Solution Approach 1:
The patent applies local quality by creating a non-uniform pore size distribution within the membrane, with different regions having optimized pore dimensions (0.5-2.0 μm range) to simultaneously provide mechanical strength where needed and high porosity (40-50%) in ion transport regions, rather than using a single uniform pore size throughout
3Productivity
If a separator is designed for high capacity and output with increased permeability, then battery performance is improved, but thermal safety is compromised due to insufficient heat resistance
Solution Approach 1:
The patent implements preliminary action by performing a multi-stage heat treatment process before the separator is installed in the battery. The first heat treatment (80-100°C) and second heat treatment (100-120°C) pre-stabilize the membrane structure, ensuring that when the battery operates at high temperatures during charging/discharging, the separator maintains its dimensional stability and does not shrink, thus preventing thermal runaway while maintaining high permeability for performance
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 membrane ensures excellent thermal safety and output properties in high-capacity batteries, passing hot-box evaluations at high temperatures and maintaining low internal resistance.
Implementation Method 1
a polyethylene microporous membrane having significantly improved heat resistance at a high temperature while having significantly high gas permeability and porosity
Implementation Method 2
a shrinkage rate in the transverse direction of 5% or less as measured after being allowed to stand at 121° C. for 1 hour
Implementation Method 3
significantly high gas permeability and porosity
Implementation Method 4
a polyethylene microporous membrane having significantly improved heat resistance at a high temperature while having significantly high gas permeability and porosity
Data Source
AI summary
Provided are a polyethylene microporous membrane, a method for manufacturing the same, and a separator including the microporous membrane. According to an embodiment, a polyethylene microporous membrane which has a thickness of 3 μm to 30 μm, a puncture strength of 0.15 N/μm or more, a shrinkage rate in the transverse direction of 5% or less as measured after being allowed to stand at 121° C. for 1 hour, and a PS index represented by the following Equation 1 of 110 or more is provided:[Equation 1]PS index=[gas permeability (×10-5 Darcy)×porosity (%)]÷[shrinkage rate (%) in the transverse direction at 121° C.].