Multi-layer Polyethylene Separator for Battery Safety

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Solution Overview

Problem

Microporous polyethylene membranes used as battery separators lack a balance of permeability, mechanical strength, heat shrinkage resistance, shutdown properties, meltdown properties, and oxidation resistance, which affects battery performance and safety.

Innovation Solution

A multi-layer microporous polyethylene membrane is developed, comprising a high-density polyethylene resin layer with a terminal vinyl group concentration of 0.2 or more and a layer with less than 0.2 terminal vinyl groups per 10,000 carbon atoms, optimized through specific molecular weight ratios and processing methods to achieve a gradient structure with controlled pore diameters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single-layer microporous polyethylene membrane is used to improve shutdown properties, then heat shrinkage resistance is improved, but mechanical strength and permeability deteriorate

Engineering Contradiction:

Improveshutdown propertiesVSAvoidmechanical strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The membrane is divided into multiple layers with different polyethylene resin compositions. Layer 1 contains polyethylene resin A with 0.2 or more terminal vinyl groups per 10,000 carbon atoms for excellent shutdown properties, while layer 2 contains polyethylene resin B with less than 0.2 terminal vinyl groups for high mechanical strength and permeability. This segmentation allows each layer to specialize in one function, resolving the contradiction between shutdown properties and mechanical strength.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the membrane have different compositions tailored to local functional requirements. The first layer has high terminal vinyl group concentration optimized for shutdown properties, while the second layer has low terminal vinyl group concentration optimized for mechanical strength and permeability. This local quality differentiation enables the membrane to simultaneously achieve contradictory properties in different locations.

Inventive Principle:

Principle #3Local quality

2Reliability

If polyethylene resin with high terminal vinyl group concentration is used to improve shutdown properties, then heat shrinkage resistance is improved, but permeability and mechanical strength deteriorate

Engineering Contradiction:

Improveshutdown propertiesVSAvoidpermeability

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The membrane structure is segmented into two layers: layer 1 with polyethylene resin A (high terminal vinyl groups ≥0.2 per 10,000 C) for shutdown properties, and layer 2 with polyethylene resin B (low terminal vinyl groups <0.2 per 10,000 C) for high permeability. This segmentation resolves the contradiction by assigning opposite functional optimizations to different layers.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The membrane exhibits local quality differentiation where the first layer has high terminal vinyl group concentration for shutdown function, while the second layer has low terminal vinyl group concentration for permeability function. This spatial variation in composition allows simultaneous achievement of contradictory properties.

Inventive Principle:

Principle #3Local quality

3Productivity

If polyethylene resin with low terminal vinyl group concentration is used to improve permeability and mechanical strength, then productivity is improved, but shutdown properties and heat shrinkage resistance deteriorate

Engineering Contradiction:

ImprovepermeabilityVSAvoidshutdown properties

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The membrane is segmented into two functional layers: layer 1 with polyethylene resin A (high terminal vinyl groups) dedicated to shutdown properties, and layer 2 with polyethylene resin B (low terminal vinyl groups) dedicated to permeability and mechanical strength. This segmentation allows the membrane to achieve both high permeability and excellent shutdown properties simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different layers of the membrane have different terminal vinyl group concentrations optimized for different functions. Layer 2 has low terminal vinyl group concentration for high permeability, while layer 1 has high terminal vinyl group concentration for shutdown properties. This local quality differentiation resolves the contradiction between permeability and shutdown properties.

Inventive Principle:

Principle #3Local quality

Data Source

PatentEP1930157B1Polyethylene multi-layer porous membrane, process for production thereof, and separators for cells

Publication Date: 2013.04.24 TORAY BATTERY SEPARATOR FILM

AI summary

A multi-layer, microporous polyethylene membrane having at least two layers, which comprises (a) a microporous polyethylene resin layer A comprising high-density polyethylene A having 0.2 or more terminal vinyl groups per 10,000 carbon atoms when measured by infrared spectroscopy, and (b) a microporous polyethylene resin layer B comprising high-density polyethylene B having less than 0.2 terminal vinyl groups per 10,000 carbon atoms when measured by infrared spectroscopy, has well-balanced permeability, mechanical strength, heat shrinkage resistance, shutdown properties, meltdown properties and oxidation resistance.