Polyolefin Multilayer Separator for Battery Thermal Safety
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Solution Overview
Problem
Conventional polyolefin multilayer microporous membranes for lithium ion secondary batteries face challenges in achieving both high mechanical strength and heat resistance, with existing solutions either compromising on shutdown temperature or meltdown temperature, and lacking sufficient electrolyte wettability.
Innovation Solution
A polyolefin multilayer microporous membrane with at least three layers, comprising a first microporous layer of ultrahigh molecular weight polyethylene as surface layers and a second microporous layer of high-density polyethylene and polypropylene as an intermediate layer, optimized for pin puncture strength, static friction coefficient, and meltdown temperature, ensuring excellent mechanical strength, electrode adhesion, and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyethylene microporous membrane is used as a separator, then the shutdown function is excellent, but the heat resistance is insufficient leading to meltdown at relatively low temperatures
Solution Approach 1:
The patent uses a multilayer composite structure combining polyethylene layers (for shutdown function) with polypropylene layers (for heat resistance). The polyethylene microporous membrane provides excellent shutdown characteristics by blocking pores at low temperatures, while the polypropylene components raise the overall meltdown temperature to at least 180°C, creating a separator that maintains both safety shutdown capability and high-temperature structural integrity.
2Strength
If the mechanical strength is enhanced by increasing membrane thickness, then the heat resistance improves, but the electrolyte wettability decreases
Solution Approach 1:
The multilayer composite structure combines thick polyethylene layers (providing mechanical strength and shutdown function) with polypropylene layers (providing heat resistance). The total thickness can be optimized for strength while the porous structure of the composite material maintains electrolyte penetration pathways, preventing the trade-off between thickness and wettability that would occur in a homogeneous membrane.
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 outstanding mechanical strength, electrolyte wettability, and heat resistance, effectively preventing thermal runaway and combustion when used as a battery separator, with a meltdown temperature of at least 180°C and a coefficient of static friction sufficient for enhanced adhesion to electrodes.
Implementation Method 1
microporous membranes comprising polyethylene resins, in particular, are known to have an excellent shutdown function, whereby the micropores of the porous membrane are blocked so as to block the flow of current when the temperature of the battery increases
Implementation Method 2
The separator prevents shorting due to contact between active materials of both polarities and holds an electrolytic solution in the pores thereof so as to form a pathway for ion conduction
Implementation Method 3
the meltdown temperature are within specific ranges... a meltdown temperature of at least 180°C... effectively preventing thermal runaway and combustion
Data Source
Figure 1~2
AI summary
To provide a polyolefin multilayer microporous membrane and a battery separator having excellent mechanical strength and heat resistance. The present invention is a polyolefin multilayer microporous membrane having at least three layers, the membrane comprising a first microporous layer composed of a polyethylene resin containing an ultrahigh molecular weight polyethylene (surface layers) and a second microporous layer composed of a polyolefin rein containing a high-density polyethylene and polypropylene (intermediate layer), wherein (I) the pin puncture strength is at least 25 g/µm, (II) the coefficient of static friction with respect to a metal foil is at least 0.40, and (III) the meltdown temperature is at least 180°C.