Crosslinked Polyolefin Separator for Thermal Stability
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Solution Overview
Problem
Conventional polyolefin separators, such as those made from polyethylene, exhibit low thermal stability, leading to dimensional instability and potential thermal runaway in lithium secondary batteries at high temperatures, which can cause internal shorts and fires.
Innovation Solution
A crosslinked polyolefin separator is developed using a method involving the preparation of a silane grafted polyolefin solution with a high molecular weight polyolefin, a diluent, and an alkoxy group containing vinylsilane, followed by extrusion, stretching, and crosslinking in the presence of water, which enhances heat resistance and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyethylene is used as separator material, then pore formation and chemical resistance are improved, but heat resistance and dimensional stability deteriorate at high temperatures
Solution Approach 1:
The patent applies composite materials by combining polyethylene with silane grafting agents and crosslinking promoters to create a crosslinked polyethylene separator. This composite structure maintains the chemical resistance of polyethylene while adding heat resistance through the crosslinked network formed by silane groups reacting with water during the heat treatment process.
Solution Approach 2:
The patent changes the physical and chemical parameters of polyethylene by introducing silane grafting during extrusion. The silane-modified polyethylene is then subjected to water exposure during heat treatment, which triggers crosslinking reactions that fundamentally alter the thermal properties while preserving the base polyethylene's chemical resistance characteristics.
2Ease of manufacture
If polyethylene is used as separator material, then low cost and excellent mechanical properties are improved, but dimensional stability deteriorates above melting point
Solution Approach 1:
The patent applies preliminary action by incorporating silane grafting agents and crosslinking promoters into the polyethylene during the extrusion process itself. This preliminary modification ensures that when the separator is subsequently exposed to water during heat treatment, the crosslinking reaction occurs in-situ, providing dimensional stability without requiring separate treatment steps.
Solution Approach 2:
The patent changes the structural parameters of polyethylene by creating a crosslinked network through silane chemistry. This crosslinked structure fundamentally alters the dimensional stability parameter, preventing shrinkage and deformation at temperatures above the original melting point while maintaining cost-effectiveness through a single-step extrusion process.
3Temperature
If crosslinking is performed using peroxide-based initiator, then heat resistance is improved, but process compatibility with stretching deteriorates
Solution Approach 1:
The patent replaces the conventional peroxide-based chemical crosslinking mechanism with a water-triggered crosslinking mechanism. This substitution allows the crosslinking reaction to occur during the heat treatment process when water is present, rather than requiring separate peroxide treatment steps that would interfere with the stretching process.
Solution Approach 2:
The patent changes the crosslinking mechanism from peroxide-initiated to water-initiated crosslinking. This parameter change in the crosslinking chemistry allows the process to be integrated into the heat treatment step that already occurs during separator manufacturing, ensuring compatibility with stretching while achieving the desired heat resistance.
4Temperature
If electron beam crosslinking is used, then heat resistance is improved, but equipment investment cost deteriorates
Solution Approach 1:
The patent employs a cost-effective crosslinking approach using readily available water and standard heat treatment equipment instead of expensive electron beam facilities. The water-triggered crosslinking mechanism uses inexpensive materials and existing manufacturing equipment, making the process economically viable for mass production.
Solution Approach 2:
The patent substitutes expensive electron beam crosslinking equipment with conventional heat treatment equipment combined with water exposure. This substitution replaces high-cost specialized equipment with standard manufacturing equipment, dramatically reducing capital investment while achieving equivalent crosslinking results through water-triggered chemistry.
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 resulting crosslinked polyolefin separator demonstrates improved high-temperature stability with a meltdown temperature above 150°C and puncture strength of 10-50 gf/μm, reducing the risk of thermal shrinkage and enhancing the safety of lithium secondary batteries.
Implementation Method 1
crosslinking the porous membrane in the presence of water
Implementation Method 2
preparation of a silane grafted polyolefin solution using a polyolefin having a weight average molecular weight higher than or equal to 200,000, a diluent, an alkoxy group containing vinylsilane, and an initiator
Data Source
AI summary
Disclosed is a method of preparing a crosslinked polyolefin separator including preparing a silane grafted polyolefin solution using a polyolefin having a weight average molecular weight higher than or equal to 200,000, a diluent, an alkoxy group containing vinylsilane, and an initiator, forming the silane grafted polyolefin solution in a sheet shape and stretching, extracting the diluent from the stretched sheet to produce a porous membrane, and crosslinking the porous membrane in the presence of water, and a crosslinked polyolefin separator.