Cross-linked Polyolefin Separator Gel Control
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Solution Overview
Problem
The existing methods for manufacturing crosslinked polyolefin separators face challenges in controlling high extruder temperatures and reducing gel content, leading to non-uniform surfaces and die-drool phenomena, which affect the performance and safety of lithium secondary batteries.
Innovation Solution
A method involving the use of non-grafted polyolefin and silane-grafted polyolefin with controlled molecular weights, along with specific alkoxysilane and phosphorus compounds, is employed to achieve reactive extrusion at higher temperatures, minimizing gel content and preventing die-drool, resulting in a separator with improved processability and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silane-grafted polyolefin with low weight average molecular weight is used to prepare crosslinked polyolefin porous membrane, then crosslinking efficiency is improved, but processability is degraded due to high gel content and difficulty in controlling extruder temperature
Solution Approach 1:
The patent changes the molecular weight parameter of silane-grafted polyolefin from low to high (300,000 or more), and adjusts the weight ratio between non-grafted and silane-grafted polyolefin (90:10 to 20:80). This parameter change reduces gel content in the extruder, improves processability, and allows better temperature control while maintaining crosslinking efficiency through the controlled presence of silane-grafted components.
Solution Approach 2:
The patent creates a composite material system combining non-grafted polyolefin and silane-grafted polyolefin in specific ratios. This composite approach allows the non-grafted component to provide good processability and low gel content, while the silane-grafted component ensures crosslinking efficiency, thus resolving the contradiction between these two properties.
2Manufacturing precision
If high temperature reactive extrusion is performed to improve polyolefin compatibility with diluting agents, then separation uniformity is improved, but die-drool phenomenon occurs and processability is degraded
Solution Approach 1:
The patent performs reactive extrusion at high temperature (200°C or higher) to improve compatibility between polyolefin and diluting agents, achieving uniform separation. The high temperature ensures complete reaction and homogeneous mixing, resolving the uniformity issue while the controlled composition prevents die-drool.
Solution Approach 2:
The patent introduces alkoxysilane compound containing carbon-carbon double bonded group (0.01-2 parts by weight based on 100 parts by weight of total weight) as a localized functional component. This localized addition provides specific chemical reactivity at the extrusion zone to prevent die-drool while maintaining the high temperature needed for uniform separation throughout the material.
3Temperature
If alkoxysilane compound content is increased to enhance crosslinking, then meltdown temperature is increased, but gel content in extruder increases and processability is degraded
Solution Approach 1:
The patent precisely controls the content of alkoxysilane compound containing carbon-carbon double bonded group within 0.01-2 parts by weight based on 100 parts by weight of total weight. This optimized parameter range provides sufficient crosslinking to increase meltdown temperature while avoiding excessive gel content formation, thus maintaining processability.
Solution Approach 2:
The patent uses a small but sufficient amount of alkoxysilane compound (0.01-2 parts by weight) rather than large amounts. This partial action provides just enough crosslinking functionality to achieve the desired meltdown temperature increase without causing excessive gel content that would degrade processability, representing an optimized balance rather than maximum possible crosslinking.
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 method enhances the compatibility of polyolefin with diluting agents, reduces gel content, and prevents die-drool, resulting in a separator with improved processability and uniformity, ensuring enhanced safety and performance for lithium secondary batteries by broadening the temperature interval between shutdown and meltdown.
Implementation Method 1
crosslinking the porous membrane in the presence of water
Implementation Method 2
carrying out reactive extrusion at 200° C. or higher to obtain a silane-grafted polyolefin composition
Implementation Method 3
extracting the diluting agent from the oriented sheet to obtain a porous membrane
Data Source
AI summary
A method for manufacturing a crosslinked polyolefin separator and the crosslinked polyolefin separator obtained therefrom are provided. The method includes non-grafted polyolefin having a weight average molecular weight of 300,000 or more and silane-grafted polyolefin having a weight average molecular weight of 300,000 or more. The method minimizes gel formation, a side reaction occurring in an extruder during the manufacture of the separator, and provides the separator having a uniform surface.