Battery Separator Coating That Limits Binder Swelling

Solution Overview

Problem

Secondary batteries face safety issues due to internal short circuits and thermal instability, particularly at high temperatures, which can lead to explosions, and existing separators fail to effectively hold inorganic particles and prevent excessive binder dissolution in electrolyte solutions, compromising mechanical durability and stability.

Innovation Solution

A separator for secondary batteries is developed with a coating layer containing polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and inorganic particles, using a polar organic solvent with a boiling point of at least 120°C to maintain appropriate lamellar thickness, enhancing mechanical strength and thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If excessive coating is applied to prevent ignition, then safety is improved, but cell capacity is reduced and cell resistance increases

Engineering Contradiction:

ImprovesafetyVSAvoidcell capacity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The invention optimizes the coating thickness parameter to a specific range (0.5-5 μm) and controls the inorganic particle content (1-20 wt%) to achieve the right balance between safety and performance. This parameter optimization prevents excessive coating while ensuring adequate thermal stability and ignition prevention.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses a composite coating layer combining organic binder (PVDF-HFP) with inorganic particles (such as Al2O3, SiO2, TiO2). This composite structure provides both the safety function of preventing ignition and the electrical properties needed to maintain cell capacity, avoiding the drawbacks of excessive single-material coating.

Inventive Principle:

Principle #40Composite materials

2Reliability

If coating layer is applied to prevent ignition, then safety is improved, but cell resistance increases

Engineering Contradiction:

ImprovesafetyVSAvoidcell resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention optimizes the coating thickness parameter to a specific range (0.5-5 μm) and controls the inorganic particle content (1-20 wt%) to achieve the right balance between safety and performance. This parameter optimization prevents excessive coating while ensuring adequate thermal stability and ignition prevention.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The coating layer is designed with a porous structure containing inorganic particles that allow electrolyte penetration. This porous architecture maintains ion transport pathways, preventing excessive resistance increase while providing the thermal stability needed for safety.

Inventive Principle:

Principle #31Porous materials

3Temperature

If separator is exposed to high temperatures, then thermal stability is tested, but separator shrinkage and damage occur causing internal short circuit

Engineering Contradiction:

Improvethermal stabilityVSAvoidseparator integrity

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The invention uses a composite coating layer combining organic binder (PVDF-HFP) with inorganic particles (such as Al2O3, SiO2, TiO2). This composite structure provides both the safety function of preventing ignition and the electrical properties needed to maintain cell capacity, avoiding the drawbacks of excessive single-material coating.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The coating layer acts as a protective cushion applied beforehand to the separator surface. This pre-applied protective layer prevents direct thermal damage and shrinkage of the separator at high temperatures, maintaining separator integrity and preventing internal short circuits during thermal events.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution effectively prevents binder swelling and maintains inorganic particle retention, improving mechanical durability, heat resistance, and overall stability of the secondary battery.

Implementation Method 1

swelling caused by the binder absorbing the electrolyte solution

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Implementation Method 2

using a polar organic solvent with a boiling point of at least 120°C

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentEP4386962B1Separator for secondary battery, secondary battery including the same, and manufacturing method of secondary battery

Publication Date: 2026.01.14 LG ENERGY SOLUTION LTD

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Figure 4A~4B

AI summary

Disclosed is a separator for a secondary battery that improves the stability of the secondary battery. In one embodiment of the present disclosure, the separator includes: a porous substrate; and a coating layer disposed on at least one surface of the porous substrate. The coating layer includes polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and inorganic particles. In the coating layer, the PVDF-HFP has a lamellar thickness of 2.5 to 3.2 nm.