Coated Battery Separator Thermal Stability

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Solution Overview

Problem

Current lithium-ion battery separators lack adequate heat resistance and shutdown characteristics, particularly when exposed to rapid temperature rises due to short-circuits, and existing solutions using heat-resistant resins do not provide sufficient safety or weight reduction.

Innovation Solution

An aqueous composition comprising salified polyamide-imide polymers and vinylidene fluoride is used to coat a substrate layer, creating a coated separator that offers improved heat resistance and shutdown functionality while reducing weight, utilizing an aqueous dispersion of vinylidene fluoride polymer with primary particles less than 1 µm in size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a polyolefin-based porous film separator is used to provide shutdown effect, then safety is improved at thermal runaway temperature, but heat resistance and dimensional stability at high temperature deteriorate

Engineering Contradiction:

ImprovesafetyVSAvoidheat resistance

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent uses a composite structure combining a polyolefin base layer (providing shutdown effect) with a heat-resistant resin coating layer (providing high-temperature stability). This composite approach allows the separator to maintain both shutdown functionality and heat resistance simultaneously.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the polyolefin separator by adding a coating layer with different thermal properties. The coating layer has a higher glass transition temperature and maintains dimensional stability at temperatures where the polyolefin base would contract, thereby changing the overall thermal parameters of the separator.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If heat-resistant resin coating is applied to improve dimensional stability, then heat resistance is improved, but weight increases

Engineering Contradiction:

Improvedimensional stabilityVSAvoidseparator weight

Core Design Contradiction:

TemperatureVSWeight of moving object

Solution Approach 1:

The patent applies a thin film coating of heat-resistant resin on the polyolefin separator. This thin coating provides the necessary dimensional stability and heat resistance without adding significant weight, as the coating layer is much thinner than the base separator layer.

Inventive Principle:

Principle #30Flexible shells and thin films

3Stability of the object's composition

If heat-resistant resin separator is used to prevent thermal contraction, then dimensional stability is improved, but shutdown characteristic is lost

Engineering Contradiction:

Improvedimensional stabilityVSAvoidshutdown characteristic

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent divides the separator into two functional segments: a polyolefin base layer that provides the shutdown effect through pore closure at low temperature, and a heat-resistant resin coating layer that provides dimensional stability at high temperature. Each layer performs its specific function without interfering with the other.

Inventive Principle:

Principle #1Segmentation

4Power

If separator thickness is reduced to improve performance, then power density is improved, but safety and reliability deteriorate

Engineering Contradiction:

Improvepower densityVSAvoidsafety

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent uses a thin coating layer of heat-resistant resin that provides enhanced safety functions without significantly increasing the overall separator thickness. This thin film approach allows the separator to maintain low thickness for high power density while still providing improved heat resistance and dimensional stability for safety.

Inventive Principle:

Principle #30Flexible shells and thin films

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 coated separator exhibits enhanced shape stability at high temperatures, provides a shutdown function for improved safety, and reduces the overall battery weight, addressing the limitations of existing separators by ensuring thermal stability and safety without increasing weight.

Implementation Method 1

an aqueous composition comprising salified polyamide-imide polymers and vinylidene fluoride is used to coat a substrate layer, creating a coated separator

Methodology Applied

Scientific EffectCoating: Coatings

Implementation Method 2

melting a resin of the separator at or below a thermal runaway (abnormal heating) temperature of the battery so as to close the pores

Methodology Applied

Scientific EffectShutdown effect: Melting

Implementation Method 3

These layers serve to prevent contact of the positive electrode and a negative electrode of the battery while permitting electrolyte to pass there through

Methodology Applied

Scientific EffectIon transport: Permeation

Data Source

PatentEP3994760B1Battery separator coating

Publication Date: 2023.08.09 SOLVAY SPECIALTY POLYMERS ITALY SPA

AI summary

The present invention pertains to an aqueous composition comprising salified polyamide-imide polymers and polyvinylidene fluoride and its use for the manufacture of electrochemical cell components, such as separators.