Microporous Polyolefin Film Composition for Stable Battery Separators

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Solution Overview

Problem

Existing microporous polyolefin films used in battery separators face challenges with thermal stability, strength, permeability, uniform quality, and productivity due to the use of ultrahigh-molecular-weight polyethylene and inorganic materials, which lead to issues like non-uniform stretching, low puncture strength, and increased extrusion load.

Innovation Solution

Manufacturing microporous polyolefin films using a composition of 20-50% resin, comprising 90-98% polyethylene with controlled molecular weight and 2-10% polypropylene, along with 50-80% diluent, followed by stretching and heat-setting, to achieve superior thermal stability and physical properties without relying on ultrahigh-molecular-weight polyethylene or inorganic materials.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If ultrahigh-molecular-weight polyethylene is used to improve strength, then puncture strength and impact strength are improved, but extrusion compoundability deteriorates and chain entanglement occurs leading to non-uniform stretching

Engineering Contradiction:

Improvepuncture strengthVSAvoidextrusion compoundability

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent changes the molecular weight parameter of polyethylene from ultrahigh-molecular-weight (greater than 700,000) to a controlled range (200,000-500,000), and controls the polydisperse index to be less than 10. This parameter optimization resolves the contradiction by achieving sufficient strength while eliminating excessive chain entanglement that causes poor extrusion compoundability and non-uniform stretching.

Inventive Principle:

Principle #35Parameter changes

2Strength

If ultrahigh-molecular-weight polyethylene is used to improve physical properties, then puncture strength is improved, but stretching uniformity deteriorates due to serious chain entanglement

Engineering Contradiction:

Improvepuncture strengthVSAvoidstretching uniformity

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent optimizes the molecular weight parameter to 200,000-500,000 and controls the polydisperse index to be less than 10, which reduces chain entanglement and enables uniform stretching while maintaining adequate puncture strength.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite resin composition by blending polyethylene (90-98 wt%) with polypropylene (2-10 wt%), where polypropylene acts as a modifier to improve stretching uniformity while the controlled molecular weight polyethylene provides the necessary strength.

Inventive Principle:

Principle #40Composite materials

3Temperature

If inorganic materials are added to improve thermal stability, then heat resistance is improved, but compoundability deteriorates and pinholes are generated

Engineering Contradiction:

Improvethermal stabilityVSAvoidcompoundability

Core Design Contradiction:

TemperatureVSEase of manufacture

Solution Approach 1:

The patent replaces inorganic materials with organic polypropylene additive, which provides thermal stability improvement without the compoundability issues and pinhole formation associated with inorganic materials. Polypropylene mixes uniformly with polyethylene and does not cause defects.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Ease of manufacture

If broad molecular weight distribution is used to improve processability, then extrusion is easier, but puncture strength and impact strength are lowered due to many defects from low molecular weight molecules

Engineering Contradiction:

Improveextrusion processabilityVSAvoidpuncture strength

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The patent optimizes the molecular weight to a specific range (200,000-500,000) and controls the polydisperse index to be less than 10, achieving a balance where the resin is processable during extrusion while maintaining high puncture strength without defects from low molecular weight molecules.

Inventive Principle:

Principle #35Parameter changes

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 resulting films exhibit high puncture strength, enhanced permeability, and improved thermal stability, with a shut-down temperature below 140°C and a melt-down temperature above 160°C, ensuring safer and more efficient battery performance and production.

Implementation Method 1

melt-extruding a composition, comprised of 20 ∼ 50 weight % of a resin composition

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 2

melt-extruding a composition

Methodology Applied

Scientific EffectExtrusion: Extrusion

Implementation Method 3

solid-liquid or liquid-liquid phase separation of polyethylene and the compatible liquid during the process of cooling

Methodology Applied

Scientific EffectPhase separation: Phase Change

Implementation Method 4

extracting the solvent

Methodology Applied

Scientific EffectExtraction: Liquid-Liquid Extraction

Implementation Method 5

heat-setting

Methodology Applied

Scientific EffectHeat treatment: Heat Treatment

Data Source

PatentEP1984435B1Microporous polyolefin film with improved meltdown property and preparing method thereof

Publication Date: 2012.05.23 SK INNOVATION CO LTD

AI summary

The present invention is related to microporous polyolefin films that may be used for battery separators and the methods of manufacturing the same. These microporous polyolefin films are characterized by consisting of 90 - 98 weight % of polyethylene (Component I) having a weight average molecular weight of 2x105 ~