Multi-layer Microporous Polyolefin Battery Separator
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Solution Overview
Problem
Microporous polyolefin membranes used in battery separators, particularly for lithium-ion batteries, often lack well-balanced shutdown properties, meltdown temperatures, permeability, and pin puncture strength, which affects battery performance and safety.
Innovation Solution
A multi-layer microporous polyolefin membrane is developed, comprising a porous polyethylene layer combined with a porous layer of polyethylene and polypropylene, where the polypropylene has a weight-average molecular weight of 6 x 10^5 or more and a heat of fusion of 90 J/g or more, with a fraction of polypropylene having a molecular weight of 1.8 x 10^6 or more being 10% or more by mass, to achieve balanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If microporous membranes are composed only of polyethylene, then low meltdown temperatures are achieved, but shutdown properties deteriorate
Solution Approach 1:
The patent applies composite materials by combining polyethylene and polypropylene in a multi-layer structure. The polyethylene layer provides low meltdown temperature for safety shutdown, while the polypropylene layer provides high meltdown temperature for structural integrity. This composite approach resolves the contradiction by allowing both low shutdown temperature (from polyethylene) and high meltdown temperature (from polypropylene) to coexist in the same membrane system.
2Temperature
If microporous membranes are composed only of polypropylene, then high shutdown temperatures are achieved, but meltdown properties deteriorate
Solution Approach 1:
The patent uses composite materials where polypropylene provides high shutdown temperature capability while polyethylene contributes to overall meltdown resistance. The multi-layer structure allows the polypropylene layer to handle shutdown function at lower temperatures while the polyethylene layer maintains structural integrity at higher temperatures, resolving the contradiction between shutdown temperature and meltdown properties.
3Reliability
If multi-layer membranes with polyethylene and polypropylene are produced, then balanced shutdown and meltdown properties are achieved, but pin puncture strength deteriorates
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure where each layer has optimized properties for its specific function. The polyethylene layer is designed with specific porosity and thickness for shutdown function, while the polypropylene layer is designed with different porosity and thickness for mechanical strength. This localized optimization allows the membrane to achieve both good shutdown properties and adequate pin puncture strength simultaneously.
Solution Approach 2:
The composite material structure combines polyethylene and polypropylene layers with specific thickness ratios and porosity distributions. The polypropylene layer provides mechanical reinforcement for pin puncture strength while the polyethylene layer maintains shutdown functionality. The synergistic combination resolves the contradiction between reliability (shutdown properties) and strength (pin puncture strength).
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 improved shutdown temperature, meltdown temperature, permeability, and pin puncture strength, enhancing the performance and safety of batteries by providing well-balanced capacity, cyclability, discharge properties, heat resistance, and compression resistance.
Implementation Method 1
microporous polyolefin membranes are widely used for various applications such as battery separators
Implementation Method 2
its performance largely affects the properties, productivity and safety of the batteries
Data Source
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Figure 3~4
AI summary
Disclosed herein is a multi-layer, microporous polyolefin membrane comprising a first porous layer of a polyethylene, and a second porous layer comprising a polyethylene, and polypropylene having a weight-average molecular weight of 6 x 105 or more and a fraction having a molecular weight of 1.8 x 106or more being 10% or more by mass.