Polyolefin Microporous Separator Membrane for Heat-Stable Battery Shutdown
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Solution Overview
Problem
Current polyolefin microporous membranes for secondary batteries lack sufficient heat resistance, mechanical strength, and permeability, especially in high-capacity batteries, leading to safety risks due to rapid temperature rises and potential meltdown.
Innovation Solution
A polyolefin microporous membrane composed of 60-80 wt% polypropylene with a viscosity average molecular weight of 1×10^6 to 3×10^6 g/mol and 20-40 wt% polyethylene with a weight average molecular weight of 1×10^5 to 10×10^5 g/mol, manufactured through a wet biaxial stretching process, achieving a puncture strength of 0.25 N/μm, gas permeability of 1.0×10^-5 Darcy, porosity of 30-70%, average pore size of 20-40 nm, shutdown temperature of 150°C or lower, and meltdown temperature of 180°C or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin microporous membrane is used as a separator in secondary batteries, then electrical insulation and ion permeability are improved, but heat resistance deteriorates leading to meltdown at high temperatures
Solution Approach 1:
The patent employs a composite structure consisting of a polyolefin microporous membrane layer and a heat-resistant coating layer. The heat-resistant coating layer contains inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder resin, creating a composite material that combines the electrical insulation and ion permeability of the polyolefin membrane with the high-temperature stability of the inorganic-containing coating, thereby preventing meltdown while maintaining functional performance
Solution Approach 2:
The patent modifies the physical and chemical parameters of the separator by controlling the thickness of the heat-resistant coating layer (1-10 μm), the size and content of inorganic particles (0.1-10 wt%), and the molecular weight and composition of the polyolefin resin. These parameter changes enable the separator to maintain its shutdown function at lower temperatures while achieving meltdown resistance at higher temperatures through optimized material composition and structure
2Temperature
If the separator is designed to have high heat resistance, then meltdown temperature is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent applies local quality by creating a heat-resistant coating layer only on the surface of the polyolefin microporous membrane, rather than throughout the entire membrane structure. This localized approach provides heat resistance where it is most needed (at the separator surface exposed to electrolyte and heat) while preserving the mechanical integrity and flexibility of the bulk polyolefin membrane structure
Solution Approach 2:
The composite structure of the heat-resistant coating layer combines inorganic particles for thermal stability with a binder resin that maintains adhesion and mechanical continuity. This composite approach ensures that the coating layer provides heat resistance without creating a brittle or weak interface that would compromise the overall mechanical strength of the separator
3Strength
If the separator is designed to have high mechanical strength, then safety is improved, but permeability deteriorates
Solution Approach 1:
The patent utilizes a thin-film heat-resistant coating layer (1-10 μm thick) that is flexible enough to conform to the underlying microporous membrane structure without blocking its pores. This thin film provides mechanical reinforcement and heat resistance while maintaining sufficient ion transport pathways through the coating's porous structure and appropriate thickness, preventing permeability deterioration
Solution Approach 2:
The heat-resistant coating layer is designed with a porous structure containing inorganic particles that create interconnected voids and channels. This porous architecture allows ions to permeate through the coating layer while the inorganic particles provide structural reinforcement, thereby simultaneously achieving high mechanical strength and maintained ion permeability
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 enhanced heat resistance, mechanical strength, and permeability, ensuring safety and performance in high-capacity batteries by maintaining a separator form at high temperatures and preventing internal short circuits.
Implementation Method 1
a polyolefin microporous membrane including 60 wt % to 80 wt % of a polypropylene having a viscosity average molecular weight of 1×10^6 g/mol to 3×10^6 g/mol and 20 wt % to 40 wt % of a polyethylene having a weight average molecular weight of 1×10^5 g/mol to 10×10^5 g/mol
Implementation Method 2
The shutdown function works by significantly increasing the resistance of the separator by melting a polyolefin to close the pores of the separator
Implementation Method 3
manufactured through a wet biaxial stretching process
Data Source
AI summary
A polyolefin microporous membrane, a method for manufacturing the same, and a separator including the microporous membrane are provided. The polyolefin microporous membrane including 60 wt % to 80 wt % of a polypropylene having a viscosity average molecular weight of 1×106 g/mol to 3×106 g/mol and 20 wt % to 40 wt % of a polyethylene having a weight average molecular weight of 1×105 g/mol to 10×105 g/mol is provided, wherein the polyolefin microporous membrane has a puncture strength of 0.25 N/μm or more, a gas permeability of 1.0×10−5 Darcy or more, a porosity of 30% to 70%, an average pore size of 20 nm to 40 nm, a shutdown temperature of 150° C. or lower, and a meltdown temperature of 180° C. or higher.