Polyethylene Microporous Separator Membrane for Heat-Stable Permeability
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Solution Overview
Problem
Existing polyethylene microporous membranes used in secondary batteries lack sufficient heat resistance, mechanical strength, and permeability, particularly in high-temperature environments, leading to safety concerns such as internal short circuits and potential fires.
Innovation Solution
A polyethylene microporous membrane with specific molecular weight, thickness, and manufacturing process, including a sequential biaxial stretching and heat treatment, to achieve improved heat resistance, mechanical strength, and permeability, ensuring a TSMD/TSTD ratio within a controlled range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyethylene microporous membrane is used as a separator in secondary batteries, then ion permeability and electrical insulation are improved, but heat resistance and mechanical strength deteriorate at high temperatures
Solution Approach 1:
The patent uses a composite structure consisting of a polyethylene microporous membrane layer and a heat-resistant porous layer. The heat-resistant porous layer contains inorganic particles (such as alumina, silica, or titania) dispersed in a binder polymer, creating a composite material that combines the ion permeability of the polyethylene membrane with the high-temperature stability of inorganic materials. This composite structure prevents membrane shrinkage and maintains mechanical strength at elevated temperatures while preserving ion transport capabilities.
Solution Approach 2:
The patent employs porous materials in both the polyethylene microporous membrane and the heat-resistant porous layer. The controlled porosity of these materials enables ion permeability while the porous inorganic network in the heat-resistant layer provides structural support at high temperatures, preventing collapse and maintaining mechanical integrity when the polyethylene component softens.
2Quantity of substance
If the battery capacity is increased for electric vehicle applications, then energy storage is improved, but safety deteriorates due to separator shrinkage at high temperatures
Solution Approach 1:
The patent applies beforehand cushioning by incorporating a heat-resistant porous layer that acts as a protective barrier against high-temperature shrinkage before it occurs. This layer is designed to maintain dimensional stability at temperatures up to 150°C or higher, preventing the polyethylene membrane from shrinking and causing internal short circuits during battery operation or abuse conditions, thereby cushioning against potential safety failures.
Solution Approach 2:
The patent changes the thermal parameters of the separator system by introducing a heat-resistant porous layer with a glass transition temperature or melting point significantly higher than the polyethylene membrane. This parameter change enables the separator to maintain its physical dimensions and functional properties at elevated temperatures, ensuring safety in high-capacity batteries that generate more heat during operation.
3Reliability
If the polyethylene microporous membrane thickness is reduced, then permeability is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent uses composite materials where a thin polyethylene microporous membrane (3-20 μm) is combined with a heat-resistant porous layer containing inorganic particles. The inorganic particle network in the heat-resistant layer provides mechanical reinforcement, compensating for the reduced thickness of the polyethylene membrane and maintaining adequate tensile strength and puncture resistance while preserving high ion permeability through the thin structure.
Solution Approach 2:
The patent applies local quality by concentrating the mechanical strength function in the heat-resistant porous layer while the thin polyethylene membrane focuses on providing ion permeability. This functional differentiation allows each layer to be optimized for its specific purpose, with the inorganic particle-reinforced layer providing localized mechanical support where needed without compromising the overall permeability of the thin-membrane structure.
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 in high-temperature conditions, preventing fuming or ignition in hot-box evaluations at 130°C, suitable for high-capacity/high-output batteries.
Implementation Method 1
a semi-crystallization time t1/2 during isothermal crystallization at 117° C. of 10-35 minutes
Implementation Method 2
a gas permeability of 1.5×10−5 Darcy or more
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 of the present disclosure, a microporous membrane is provided which includes a polyethylene having a weight average molecular weight of 1×105 g/mol to 10×105 g/mol, and has a thickness of 3 μm to 20 μm, a puncture strength of 0.25 N/μm or more, a gas permeability of 1.5×10−5 Darcy or more, a shrinkage rate in the transverse direction of 10% or less as measured after being allowed to stand at 131° C. for 1 hour, a tensile strength in the machine direction of 1500 kg/cm2 or more, a tensile strength in the transverse direction of 2000 kg/cm2 or more, and a ratio between the tensile strength in the machine direction and the tensile strength in the transverse direction of 0.5 to 0.7.