Polyolefin Battery Separator Shrinkage Resistance

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Microporous polyolefin membranes used in battery separators lack sufficient melting shrinkage resistance, leading to short-circuiting at elevated temperatures, despite having shutdown and meltdown properties.

Innovation Solution

A microporous polyolefin membrane is developed with a polyethylene resin having a shutdown temperature of 135°C or lower, achieved by melt-blending with a membrane-forming solvent to create a polyolefin resin solution with specific viscoelastic properties, which is then extruded, cooled, and solvent-removed to form a gel-like sheet, ensuring a maximum melting shrinkage ratio of 40% or less and a meltdown temperature of 150°C or higher.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the membrane structure is optimized for pore closure, then shutdown properties improve, but mechanical strength and shape stability at high temperatures deteriorate

Engineering Contradiction:

Improveshutdown propertiesVSAvoidshape stability at high temperature

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The invention applies preliminary action by incorporating specific additives (nucleating agents, antioxidants, and processing aids) into the polyethylene resin matrix before membrane formation. These additives pre-establish the crystalline structure and thermal properties of the membrane, ensuring that when the battery experiences elevated temperatures, the membrane has already been prepared to maintain its shape and mechanical strength. The nucleating agents, in particular, pre-organize the polymer chains to resist shrinkage during thermal events.

Inventive Principle:

Principle #10Preliminary action

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 excellent shutdown properties, melting shrinkage resistance, and meltdown properties, providing enhanced stability and preventing short-circuiting in batteries, while maintaining high permeability and mechanical strength.

Implementation Method 1

a property of closing pores by heat generation in batteries to stop battery reactions (shutdown properties)... a polyethylene resin having a temperature of 135°C or lower, at which a crystal-melting calorie measured by differential scanning calorimetry reaches 60% of the total crystal-melting calorie

Methodology Applied

Scientific EffectCrystal melting: Melting

Implementation Method 2

melt-blending a polyolefin resin comprising the above polyethylene resin with a membrane-forming solvent, to prepare a polyolefin resin solution... which is then extruded, cooled, and solvent-removed to form a gel-like sheet

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentEP1956041B1Microporous polyolefin membrane, process for producing the same, separator for cell, and cell

Publication Date: 2012.01.11 TORAY BATTERY SEPARATOR FILM

Figure 1~2
Figure 3
Figure 4

AI summary

A microporous polyolefin membrane comprising a polyethylene resin, and having (a) a shutdown temperature of 135°C or lower, at which the air permeability measured while heating at a temperature-elevating speed of 5°C/minute reaches 1 x 105 sec/100 cm3, (b) a maximum melting shrinkage ratio of 40% or less in a transverse direction in a temperature range of 135 to 145°C, which is measured by thermomechanical analysis under a load of 2 gf and at a temperature-elevating speed of 5°C/minute, and (c) a meltdown temperature of 150°C or higher, at which the air permeability measured while further heating after reaching the shutdown temperature becomes 1 x 105 sec/100 cm3 again.