Multi-layer Microporous Polyolefin Membrane for Battery Separators
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Solution Overview
Problem
Microporous polyolefin membranes with polypropylene in surface layers suffer from poor film formability, thickness uniformity, high shutdown temperatures, and low shutdown speeds, leading to safety issues and low productivity in battery separators.
Innovation Solution
A multi-layer microporous polyolefin membrane with both surface layers composed of polyethylene resin and an inner layer of polyethylene and polypropylene, where the polypropylene has a heat of fusion of 90 J/g or more, achieving low shutdown temperatures, high shutdown speeds, and high meltdown temperatures, along with excellent film formability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polypropylene is added to surface layers to improve meltdown properties, then high-temperature strength is improved, but film formability deteriorates and thickness uniformity worsens
Solution Approach 1:
The membrane is divided into multiple layers with different compositions: surface layers containing polyethylene and polypropylene for high-temperature strength, and inner layers containing only polyethylene for good film formability and thickness uniformity. This segmentation allows each layer to perform its specific function without compromising overall performance.
Solution Approach 2:
Different regions of the membrane have different material compositions tailored to their specific functions. The surface layers have polypropylene for heat resistance where it is most needed, while the inner layers have pure polyethylene for manufacturing quality where film formability is critical.
2Temperature
If polypropylene content in surface layers is increased to improve meltdown properties, then high-temperature strength is improved, but shutdown temperature increases and shutdown speed decreases
Solution Approach 1:
The membrane structure separates the shutdown function (handled by polyethylene in inner layers with low melting point) from the meltdown function (handled by polypropylene in surface layers). This segmentation allows the polyethylene to provide fast shutdown response while polypropylene provides high-temperature strength.
Solution Approach 2:
The membrane uses a composite structure combining polyethylene and polypropylene in specific layers. The polyethylene component ensures low shutdown temperature and high shutdown speed, while the polypropylene component in surface layers ensures high meltdown temperature and dimensional stability.
3Stability of the object's composition
If polypropylene is added to improve high-temperature strength, then dimensional stability is improved, but film formability deteriorates
Solution Approach 1:
The membrane is segmented into surface layers with polypropylene for dimensional stability and inner layers with pure polyethylene for ease of manufacture and good film formability. This allows each region to optimize for its specific requirement.
Solution Approach 2:
Polypropylene is locally placed in surface layers where dimensional stability is most critical for maintaining separator shape at high temperatures, while the inner layers maintain pure polyethylene composition for manufacturing quality and film formability.
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 and meltdown properties, mechanical strength, permeability, and dimensional stability, enhancing battery safety and productivity.
Implementation Method 1
a function of closing pores at the time of abnormal heat generation to stop a battery reaction [shutdown (SD) property]
Implementation Method 2
a function of keeping the shape of the separators even at high temperatures to prevent the direct reaction of cathode materials and anode materials (dimensional stability)
Data Source
AI summary
A multi-layer, microporous polyolefin membrane having at least three layers, which comprises first microporous layers made of a polyethylene resin for constituting at least both surface layers, and at least one second microporous layer comprising a polyethylene resin and polypropylene and disposed between both surface layers, the heat of fusion (ΔHm) of the polypropylene measured by differential scanning calorimetry being 90 J/g or more, and the polypropylene content in the second microporous layer being 50% or less by mass based on 100% by mass of the total of the polyethylene resin and the polypropylene.