Polyethylene Microporous Separator for Permeability and Heat Resistance
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Solution Overview
Problem
Conventional polyethylene microporous membranes face a conflicting relationship between high permeability and heat resistance, failing to meet the requirements for high-capacity and high-power batteries, particularly in terms of thermal safety and mechanical strength.
Innovation Solution
A polyethylene microporous membrane with a thickness of 3-30 um, puncture strength of 0.15 N/um or more, and a PS index of 110 or more, manufactured using a wet method involving sequential biaxial stretching and specific heat treatment processes, achieving improved heat resistance, gas permeability, and porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional separator implements high permeability to improve capacity and power properties, then gas permeability is improved, but heat resistance and mechanical strength deteriorate
Solution Approach 1:
The patent applies parameter changes by optimizing the molecular weight distribution of polyethylene (specifically using a bimodal distribution with Mw/Mn ratio of 3.0-6.0), controlling crystallinity between 40-60%, and adjusting pore size distribution to achieve both high gas permeability and improved heat resistance. This resolves the contradiction by changing material parameters rather than simply increasing permeability at the cost of thermal stability.
Solution Approach 2:
The patent uses composite material approach by creating a microporous membrane with specific polyethylene composition that combines different molecular weight components. The composite structure achieves synergistic effects where the material simultaneously provides high ion permeability through optimized pore structure and enhanced heat resistance through controlled crystallinity and molecular architecture.
2Use of energy by moving object
If a microporous membrane is made into a thin film to reduce resistance, then internal resistance is reduced, but mechanical strength and heat resistance deteriorate
Solution Approach 1:
The patent changes material parameters by optimizing thickness to 3-30 μm while simultaneously controlling puncture strength to 0.15 N/μm or more through specific molecular weight distribution and crystallinity control. This allows thin film construction for low resistance while maintaining adequate mechanical strength through enhanced material properties.
Solution Approach 2:
The patent applies local quality by creating regions with different pore sizes and densities within the membrane structure. This allows the thin film to provide low resistance pathways for ion transport while maintaining structural integrity through strategically distributed stronger regions, achieving both low internal resistance and sufficient mechanical strength.
3Productivity
If pore diameter is increased to improve ion permeability, then gas permeability is improved, but mechanical strength and heat shrinkage resistance deteriorate
Solution Approach 1:
The patent optimizes pore diameter to 0.03-1.0 μm rather than using uniformly large pores. This controlled pore size distribution, combined with specific crystallinity (40-60%), achieves high ion permeability while maintaining mechanical strength and heat shrinkage resistance through the balanced microstructure.
Solution Approach 2:
The patent employs porous material science by creating a controlled microporous structure with specific pore size distribution rather than simply increasing pore diameter. The porous structure provides ion transport pathways while the surrounding matrix maintains mechanical integrity, resolving the contradiction between permeability and 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 membrane provides excellent thermal safety and power performance, preventing battery fuming or ignition in hot-box evaluations at high temperatures, while maintaining low internal resistance and high output characteristics.
Implementation Method 1
the microporous membrane according to an embodiment may be manufactured by a wet method including a sequential biaxial stretching process
Implementation Method 2
a polyethylene microporous membrane which has a thickness of 3 um to 30 μm, a puncture strength of 0.15 N/um 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
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 um 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 (×10-5 Darcy) × porosity (%)] ÷ [shrinkage rate (%) in the transverse direction at 121 °C].