Polyethylene Microporous Membrane for Heat-Stable Battery Separators
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Solution Overview
Problem
Conventional polyethylene microporous membranes used as separators in secondary batteries face a challenge in achieving both high heat resistance and gas permeability due to their inverse relationship, limiting their application in high-capacity and high-output batteries.
Innovation Solution
A polyethylene microporous membrane with a thickness of 3 μm to 30 μm, puncture strength of 0.15 N/μm or more, and a PS index of 110 or more, manufactured through a sequential biaxial stretching process that includes extracting diluent before stretching in the transverse direction, enhances heat resistance and gas permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the gas permeability is increased to improve capacity and output, then the porosity is improved, but the 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 by controlling the weight average molecular weight (1×10^5 to 10×10^5 g/mol) and implementing a specific sequential biaxial stretching process with controlled temperature and tension parameters. This results in a membrane with gas permeability of 10.0×10^-5 Darcy or more while maintaining shrinkage rate of 5% or less at 121°C, thereby resolving the inverse relationship between gas permeability and heat resistance
Solution Approach 2:
The patent creates a composite structure within the polyethylene membrane through sequential biaxial stretching, forming a network of micropores with specific size distribution and spatial arrangement. This composite microstructure enables simultaneous achievement of high gas permeability (10.0×10^-5 Darcy or more) and high heat resistance (shrinkage rate 5% or less), effectively combining the benefits of both properties
2Quantity of substance
If the porosity is increased to improve ion permeability, then the ion conductivity is improved, but the mechanical strength deteriorates
Solution Approach 1:
The patent optimizes the porosity parameter to a specific range (40% to 70%, preferably 50% to 60%) and controls the pore size distribution through molecular weight selection and stretching parameters. This parameter optimization achieves high ion conductivity while maintaining puncture strength of 0.15 N/μm or more, resolving the trade-off between porosity and mechanical strength
Solution Approach 2:
The patent creates local quality variations in the membrane structure through sequential biaxial stretching, forming regions with different pore sizes and densities. The membrane contains both large pores for ion transport and smaller pores for structural support, enabling simultaneous achievement of high porosity (50% to 60%) and adequate mechanical strength (puncture strength 0.15 N/μm or more)
3Volume of moving object
If the separator size is increased to accommodate high-capacity batteries, then the battery capacity is improved, but the thermal safety deteriorates due to increased shrinkage risk at high temperature
Solution Approach 1:
The patent changes the thermal parameters of the polyethylene membrane by selecting specific molecular weight ranges (1×10^5 to 10×10^5 g/mol) and controlling the crystalline structure through heat treatment at specific temperatures (90°C to 110°C). These parameter changes enable large separators (30 μm to 100 μm thickness) to maintain dimensional stability with shrinkage rate of 5% or less at 121°C, ensuring thermal safety in high-capacity batteries
Solution Approach 2:
The patent applies preliminary heat treatment and stretching to the membrane before final assembly, pre-establishing the crystalline structure and dimensional stability. This preliminary action ensures that even when the separator is scaled up for high-capacity batteries, the shrinkage rate remains controlled at 5% or less at 121°C, preventing thermal runaway
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 achieves improved thermal safety and output properties in high-capacity batteries by maintaining a shrinkage rate of 5% or less and gas permeability of 10.0×10−5 Darcy or more, ensuring low internal resistance and high ion conductivity.
Implementation Method 1
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 2
a gas permeability of 10.0×10−5 Darcy or more
Implementation Method 3
high permeability and high porosity is required to improve a capacity and output
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:PS index=[gas permeability (×1031 5 Darcy)×porosity (%)]+[shrinkage rate (%) in the transverse direction at 121° C.]. [Equation 1]