Crosslinked Polyolefin Separator With Uniform Pore Crosslinking
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Solution Overview
Problem
Conventional silane crosslinked polyolefin separators face issues with gel formation, non-uniform crosslinking, and thickness deviation during extrusion, leading to mechanical strength degradation and non-uniform lithium ion transport.
Innovation Solution
A method involving the application of a coating solution containing an initiator and alkoxy group-containing vinylsilane onto a polyolefin porous membrane, followed by thermal fixing and crosslinking in the presence of water, allowing for uniform silane crosslinking within the pores and controlled thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If silane grafting and extrusion are performed simultaneously during the extrusion of polyolefin composition, then crosslinking is achieved, but gel formation increases and crosslinking control becomes difficult
Solution Approach 1:
The patent divides the crosslinking process into two separate stages: first, silane grafting during extrusion to introduce crosslinking sites; second, post-extrusion crosslinking in a controlled environment. This segmentation prevents premature crosslinking reactions that cause gel formation while ensuring uniform crosslinking distribution in the final product.
Solution Approach 2:
The patent performs silane grafting as a preliminary action during the extrusion process, preparing the polyolefin with crosslinking capability before the actual crosslinking occurs. This preliminary introduction of silane groups allows for controlled crosslinking later without the harmful side effects of simultaneous crosslinking during extrusion.
2Productivity
If polyolefin, diluting agent, crosslinking agent, and initiator are introduced to extruder at once, then reactive extrusion is achieved, but side reactions occur and gel formation increases
Solution Approach 1:
The patent segments the material introduction process: polyolefin and diluting agent are introduced during extrusion for porosity formation, while crosslinking agent and initiator are introduced separately in a subsequent step. This prevents unwanted side reactions between all components occurring simultaneously in the extruder.
Solution Approach 2:
The patent extracts the crosslinking agents and initiators from the extrusion process itself, introducing them only after extrusion is complete. This separation removes the potential for harmful side reactions during extrusion while maintaining the benefits of reactive extrusion for the polyolefin-diluting agent system.
3Manufacturing precision
If diluting agent, crosslinking agent, and initiator are extracted after reactive extrusion, then porosity is achieved, but crosslinking control is lost and uniformity decreases
Solution Approach 1:
The patent performs silane grafting as a preliminary action during extrusion, uniformly distributing crosslinking sites throughout the porous structure before porosity development. This ensures that when crosslinking occurs later, it does so uniformly throughout the material without compromising porosity uniformity.
Solution Approach 2:
The patent applies crosslinking agents and initiators locally to the porous structure after extrusion, ensuring that crosslinking occurs uniformly throughout the three-dimensional porous network. This localized application maintains both porosity uniformity and crosslinking uniformity by treating the entire porous structure evenly.
4Productivity
If conventional extrusion method is used, then production efficiency is maintained, but thickness deviation in width direction occurs
Solution Approach 1:
The patent modifies extrusion parameters including temperature profile, extrusion speed, and die design to minimize thickness deviation during extrusion. These parameter changes maintain high production efficiency while achieving uniform thickness across the width of the separator.
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 results in a crosslinked polyolefin separator with reduced gel formation, uniform crosslinking, and improved mechanical strength, enabling effective lithium salt transport and enhanced safety in electrochemical devices.
Implementation Method 1
a crosslinked polyolefin separator which includes silane-crosslinked polyolefin
Implementation Method 2
crosslinking in the presence of water
Implementation Method 3
high ion conductivity for increasing lithium ion permeability based on high porosity
Data Source
AI summary
A crosslinked polyolefin separator which has gels with a longer side length of 50 μm or more in a number ranging from 0 to 3 per 1 m2 of the separator, and shows a standard deviation of absorbance ratio between the center of the separator and the side thereof ranging from 0.01 to 0.5 is provided. A method for manufacturing the crosslinked polyolefin separator is also provided. The method includes (S1) preparing a polyolefin porous membrane, and (S2) applying a coating solution containing an initiator and alkoxy group-containing vinylsilane onto at least one surface of the porous membrane. The coating solution can permeate even to the inside of exposed pores. Thus, it is possible to provide a crosslinked polyolefin separator in which silane crosslinking occurs uniformly even inside of the pores.