Polypropylene Microporous Membrane for Heat-Resistant Battery Separators
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Solution Overview
Problem
Conventional polypropylene microporous membranes used in secondary batteries have low puncture strength, large pore size, and poor heat resistance, making them unsuitable for high-capacity batteries due to safety concerns in high-temperature environments.
Innovation Solution
A polypropylene microporous membrane with a viscosity average molecular weight of 1×10^6 to 3×10^6 g/mol, manufactured using a wet method with sequential biaxial stretching and heat treatment, achieving a thickness of 3-30 μm, puncture strength of 0.20 N/μm or more, gas permeability of 1.0×10^-5 Darcy or more, porosity of 25-60%, and a shrinkage rate of 20% or less at 150°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polypropylene microporous membrane is manufactured by a dry method, then the manufacturing process is simple, but the puncture strength is low and pore size uniformity is poor
Solution Approach 1:
The patent changes the manufacturing method from dry to wet process, and modifies stretching parameters (sequential biaxial stretching with specific stretch ratios of 3-10 times in machine direction and 2-8 times in transverse direction) to achieve high puncture strength (0.08 N/μm or more) while maintaining manufacturing feasibility
Solution Approach 2:
The patent uses a composite structure consisting of a polypropylene base layer with controlled crystallinity (30-70%) combined with specific stretching treatment, creating a composite microstructure that achieves both high strength and uniform pore distribution
2Strength
If the thickness of the microporous membrane is increased to improve puncture strength, then the mechanical strength improves, but the permeability decreases
Solution Approach 1:
The patent optimizes the thickness parameter to 3-30 μm range and combines it with controlled porosity (30-70%) and pore size (0.01-1 μm) to achieve the balance where puncture strength is 0.08 N/μm or more while maintaining high ion permeability
Solution Approach 2:
The patent utilizes a porous structure with controlled pore size distribution (0.01-1 μm) and porosity (30-70%) that provides both mechanical strength through the polypropylene matrix and high ion permeability through the interconnected pore network
3Quantity of substance
If a polyethylene is used as separator material, then the ion permeability is good, but the heat resistance is insufficient due to low melting temperature
Solution Approach 1:
The patent changes the material from polyethylene to polypropylene, which has a higher melting point and glass transition temperature, achieving heat resistance (shrinkage rate of 20% or less at 150°C) while maintaining ion permeability through optimized pore structure
4Quantity of substance
If a polypropylene microporous membrane has high porosity to improve permeability, then the ion permeability improves, but the mechanical strength decreases
Solution Approach 1:
The patent optimizes porosity to 30-70% range and combines it with controlled pore size (0.01-1 μm) and thickness (3-30 μm) to achieve the balance where ion permeability is enhanced while puncture strength remains 0.08 N/μm or more
Solution Approach 2:
The patent creates different local structures within the membrane: a dense polypropylene matrix providing mechanical strength and a controlled porous network providing ion permeability, with crystallinity controlled at 30-70% to balance both requirements
5Quantity of substance
If the microporous membrane is made into a thin film to improve battery energy density, then the permeability improves, but the puncture strength decreases
Solution Approach 1:
The patent optimizes thickness to 3-30 μm range and combines it with controlled porosity (30-70%) and pore size (0.01-1 μm) to achieve high ion permeability in thin films while maintaining puncture strength of 0.08 N/μm or more
Solution Approach 2:
The patent uses a porous structure with optimized pore size (0.01-1 μm) that provides efficient ion transport pathways in thin films while the polypropylene matrix maintains sufficient mechanical 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 exhibits excellent puncture strength, permeability, and heat resistance, ensuring battery safety and performance in high-temperature environments, passing hot-box evaluations at 140°C and preventing thermal runaway.
Implementation Method 1
sequential biaxial stretching
Implementation Method 2
heat treatment
Implementation Method 3
crystallinity of 30% to 70%
Implementation Method 4
gas permeability of 1.0×10^-5 Darcy or more
Data Source
Figure 1~2
AI summary
Provided are a polypropylene microporous membrane, a method for manufacturing the same, and a separator including the microporous membrane. According to an embodiment, a polypropylene microporous membrane including a polypropylene having a viscosity average molecular weight of 1×106 g/mol to 3×106 g/mol, wherein the microporous membrane has a thickness of 3 um to 30 um, a puncture strength of 0.20 N/um or more, a gas permeability of 1.0×10-5 Darcy or more, a porosity of 25% to 60%, an average pore size of 25 nm to 50 nm, and a shrinkage rate in the transverse direction of 20% or less as measured after being allowed to stand at 150°C for 1 hour, is provided.