Multilayer Polyethylene Battery Separators for Heat Stability and Strength
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Solution Overview
Problem
Electron beam irradiation of polyethylene membranes for lithium ion batteries improves high temperature performance but causes chain scission reactions, leading to weakened membrane strength, particularly at higher doses.
Innovation Solution
A multilayer porous membrane structure is developed, comprising a dry-process polyethylene layer treated with electron-beam radiation and an additional untreated layer, with an optional blocking layer to mitigate the negative effects of irradiation, and the use of additives that allow cross-linking at lower irradiation doses, along with co-extruded polyethylene layers and surface coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If electron beam irradiation is applied to polyethylene membranes to improve high temperature performance, then cross-linking occurs which improves high temperature performance, but chain scission reactions also occur which weaken the membrane
Solution Approach 1:
The patent applies electron beam irradiation selectively to specific layers of the multilayer membrane structure. The first polyethylene layer receives the irradiation dose to achieve cross-linking and improved high temperature performance, while the second polyethylene layer remains untreated to maintain high strength and resist chain scission. This localized application of the irradiation process resolves the contradiction by allowing each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent creates a composite multilayer membrane structure combining two different polyethylene layers with distinct properties. One layer is electron beam irradiated to provide high temperature stability through cross-linking, while the other layer remains non-irradiated to provide mechanical strength. The synergistic combination of these two layers in a single composite structure allows the membrane to simultaneously achieve both improved high temperature performance and maintained strength.
2Reliability
If higher doses of electron beam irradiation are applied to achieve better cross-linking, then high temperature performance improves, but chain scission reactions become more prevalent which weakens the membrane further
Solution Approach 1:
The patent divides the membrane into multiple layers, allowing the electron beam irradiation process to be applied segmentally rather than uniformly across the entire membrane. By concentrating the irradiation dose on specific layers that benefit most from cross-linking while leaving other layers untreated, the patent achieves the necessary high temperature performance without subjecting the entire membrane structure to high doses that would cause excessive chain scission and weakening.
Solution Approach 2:
Different layers of the membrane are given different treatments - one layer receives high dose electron beam irradiation for cross-linking and heat resistance, while another layer remains untreated to maintain mechanical integrity. This local differentiation of treatment quality allows the system to optimize for both reliability at high temperature and structural strength without the trade-off that would exist in a uniformly treated membrane.
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 solution enhances the membrane's strength and stability while maintaining the benefits of electron-beam irradiation, such as improved safety and high temperature performance, by minimizing chain scission reactions and optimizing the irradiation dosage.
Implementation Method 1
Electron beam irradiation has been applied to membranes comprising polyethylene
Implementation Method 2
Electron beam irradiation causes cross-linking, which among other things, improves the high temperature performance of the film
Implementation Method 3
However, electron beam Irradiation also causes chain scission reactions to occur. Chain scission results in beneficial properties, such as lowering of the shutdown temperature resulting in improved safety when the membrane is used as a battery separator, but also results in weakening of the membrane
Data Source
AI summary
This application is directed to dry-process porous membranes comprising polyethylene and to methods for forming such membranes. Some of the dry-process porous membranes may comprise polyethylene that has been irradiated with electron-beam irradiation. The dry-process porous membranes disclosed herein may be used in the following: lithium ion batteries, including those utilizing nickel manganese cobalt oxide (NMC), lithium metal, or lithium iron phosphate (LFP) chemistries, and/or large format lithium ion batteries, textiles, garments, PPE, filters, medical products, house products, fragrance devices, and/or disposable lighters. In at least one embodiment, a multilayer porous membrane, comprises a dry-process polyethylene layer that has been treated with electron-beam radiation; and, an additional layer that has not been treated with electron-beam irradiation; and, optionally: wherein a dosage of the electron-beam radiation is from 20 kGy to 250 kGy, 50 kGy to 250 kGy, from 60 kGy to 200 kGy, from 70 kGy to 150 kGy, or from 80 kGy to 140 kGy; wherein the additional layer is laminated to the dry-process polyethylene layer that has been treated with electron-beam radiation; or wherein a blocking layer is laminated with a dry-process polyethylene layer and the additional layer to form a structure with the blocking layer between the dry-process polyethylene layer and the additional layer, and wherein the dry-process polyethylene layer is treated with electron beam irradiation to form the dry-process polyethylene layer that has been treated with electron-beam radiation. Also described is a textile, garment, PPE, filter, medical product, house product, fragrance device, or disposable lighter comprising the inventive membrane.