Polyolefin Resin Composition for Microporous Battery Separators
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Solution Overview
Problem
Existing polyolefin microporous membranes, particularly for lithium ion batteries, face challenges with mechanical strength, thermal resistance, and fisheyes, which can lead to safety issues such as short circuits and dendrite growth due to uneven ion permeability and high melting points, making them unsuitable for reliable battery separators.
Innovation Solution
A polyolefin resin composition comprising ultra-high molecular weight ethylene polymer, 4-methyl-1-pentene or 3-methyl-1-pentene polymer, and an olefin polymer with 2 to 12 carbon atoms, along with an additional olefin polymer of specific molecular weight, is developed to enhance mechanical properties, thermal resistance, and reduce fisheyes, enabling the production of a microporous membrane with improved shutdown and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultra-high molecular weight polyethylene is used to enhance mechanical strength, then mechanical strength is improved, but thermal resistance deteriorates due to low melting point
Solution Approach 1:
The patent uses a composite material system combining ultra-high molecular weight polyethylene (for mechanical strength) with polypropylene and polymethylpentene (for high melting point and thermal resistance). This composite approach allows the separator to simultaneously achieve both high mechanical strength and high thermal resistance, resolving the contradiction between these two properties.
2Temperature
If high-density polyethylene and polymethylpentene are mixed to improve thermal resistance, then thermal resistance is improved, but manufacturing precision deteriorates due to poor compatibility causing fisheyes
Solution Approach 1:
The patent introduces an olefin copolymer as a compatibility promoter (intermediary) to improve the compatibility between high-density polyethylene and polymethylpentene. This copolymer acts as a bridge that enhances interfacial adhesion between the incompatible polymers, preventing fisheye formation and ensuring uniform film structure during the stretching process, thus resolving the manufacturing precision issue while maintaining thermal resistance.
3Reliability
If polyethylene microporous membranes are used for shutdown properties, then shutdown properties are improved, but mechanical strength deteriorates
Solution Approach 1:
The patent changes the molecular weight parameter by using ultra-high molecular weight polyethylene instead of conventional polyethylene. This parameter change provides both the low melting point needed for shutdown properties and the high mechanical strength required for separator integrity, simultaneously improving both shutdown properties and mechanical strength.
4Temperature
If polymethylpentene is added to improve meltdown temperature, then thermal resistance is improved, but ease of manufacture deteriorates due to poor compatibility requiring complex processing
Solution Approach 1:
The olefin copolymer serves as a compatibility promoter that facilitates the mixing and processing of polymethylpentene with polyethylene. By improving compatibility at the molecular level, the copolymer enables smooth melt processing and uniform film formation, significantly reducing processing difficulty and improving ease of manufacture while maintaining the high meltdown temperature benefits.
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 composition results in a microporous membrane with excellent mechanical properties, thermal resistance, and reduced fisheyes, ensuring safe and efficient battery operation by maintaining structural integrity and uniform ion conductivity, thus preventing dangerous short circuits and dendrite growth.
Implementation Method 1
a polyolefin microporous membrane formed of ultra-high molecular weight polyethylene has been proposed for an enhancement in the mechanical strength
Implementation Method 2
the membranes are melted at a relatively low temperature owing to heat generated by the short-circuit current to close the micropores with the result that the battery circuits can be shut down
Data Source
AI summary
There are provided a polyolefin resin composition having excellent mechanical properties and thermal resistance; a film formed of the polyolefin resin composition, which has excellent mechanical properties and thermal resistance and which is less likely to suffer from fisheyes; a microporous membrane having excellent permeability and shutdown properties in addition to the above-mentioned physical properties; and applications thereof. Such objects are accomplished by a polyolefin resin composition containing an ultra-high molecular weight ethylene polymer (A), a 4-methyl-1-pentene polymer or 3-methyl-1-pentene polymer (B), and a polymer of an olefin having 2 to 12 carbon atoms (C) at an intended ratio.