Polypropylene Microporous Membrane Heat Shrinkage Resistance
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Solution Overview
Problem
Existing battery separator films face challenges with high temperature-induced heat shrinkage, leading to potential internal short circuits in batteries, as they soften and lose dimensional stability, especially near the edges, which is not reliably predicted by standard heat shrinkage tests at 105°C.
Innovation Solution
A multi-layer microporous membrane composed of polypropylene with a weight-average molecular weight greater than 0.9×10^6, featuring a heat shrinkage of ≤8.0% at 130°C and optimized layer structure and stretching processes to enhance dimensional stability and pin puncture strength, is developed. The membrane includes layers of polyethylene and polypropylene with specific molecular weights and diluents, and undergoes controlled stretching and drying to achieve improved thermal and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard heat shrinkage tests at 105°C are used to evaluate separator films, then the testing process is simple and quick, but the test results do not reliably predict actual high-temperature performance and dimensional stability
Solution Approach 1:
The patent changes the test temperature parameter from 105°C to 130°C to better reflect actual battery operating conditions. This parameter change improves the predictive accuracy of heat shrinkage tests while maintaining the simplicity of the testing methodology.
2Stability of the object's composition
If polypropylene with high molecular weight (>0.9×10^6) is used to reduce heat shrinkage at elevated temperatures, then dimensional stability improves, but manufacturing complexity increases due to controlled stretching and drying processes
Solution Approach 1:
The patent applies preliminary stretching and drying actions during the manufacturing process to establish the desired membrane structure before final assembly. This preliminary structuring ensures dimensional stability at high temperatures while managing manufacturing complexity through process integration.
Solution Approach 2:
The patent uses composite material structure with polypropylene as the base polymer and incorporates specific additives and layer configurations. This composite approach enhances dimensional stability and heat resistance while allowing optimization of manufacturing parameters.
3Reliability
If multi-layer structure with polyethylene and polypropylene is implemented to enhance thermal properties, then heat shrinkage resistance improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the separator membrane into multiple functional layers with polyethylene and polypropylene. Each layer has specific thickness and composition ratios that are controlled during co-extrusion, achieving reliable heat shrinkage resistance while managing manufacturing precision through process design.
Solution Approach 2:
The patent applies local quality by having different layers with distinct properties - polyethylene layers provide low-temperature shutdown function while polypropylene layers provide high-temperature structural stability. This local differentiation optimizes overall performance while allowing each layer to be manufactured within achievable precision limits.
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 enhanced resistance to heat shrinkage at elevated temperatures, maintaining dimensional stability and pin puncture strength, effectively preventing internal short circuits in batteries and ensuring reliable performance across a broader temperature range.
Implementation Method 1
stretching a multi-layer layer extrudate in at least one of MD or TD
Implementation Method 2
removing at least a portion of the first and second diluents from stretched extrudate to produce a dried membrane
Data Source
AI summary
A method of producing microporous membranes includes stretching a multi-layer layer extrudate having first and second layers, the first layer including a first polyolefin and a first diluent, and the second layer including a second polyolefin and a second diluent, the second polyolefin including polypropylene in an amount of 1.0 wt. % to 40.0 wt. %, the polypropylene having an Mw>0.9×106 and a ΔHm≧100.0 J/g; removing at least a portion of the diluents to produce a dried membrane having a first length and a first width; stretching the membrane by a first magnification factor of 1.1 to 1.5 and stretching the membrane by a second magnification factor of 1.1 to 1.3; and reducing the width.