Battery Separator Mixed Layer for Strength and Flexibility

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Solution Overview

Problem

Conventional nonaqueous electrolyte secondary battery separators have insufficient mechanical strength, particularly after the heat-resistant layer is peeled off from the polyolefin porous film, which affects their performance and safety.

Innovation Solution

A nonaqueous electrolyte secondary battery separator with a mixed layer containing a heat-resistant resin and a porous base material, where the heat-resistant resin is uniformly distributed in a specific gradation within the thickness direction, enhancing mechanical strength and flexibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a heat-resistant layer is formed on a polyolefin porous film, then heat resistance is improved, but mechanical strength deteriorates after the heat-resistant layer is peeled off

Engineering Contradiction:

Improveheat resistanceVSAvoidmechanical strength

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The heat-resistant resin is caused to penetrate into the polyolefin porous film before the heat-resistant layer is formed, creating a mixed layer that serves as an anchor. This preliminary penetration action ensures that when the heat-resistant layer is later peeled off, the polyolefin porous film retains sufficient mechanical strength due to the embedded heat-resistant resin network.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention creates a composite structure where heat-resistant resin and polyolefin-based resin are mixed in the mixed layer. This composite material approach allows the separator to combine the heat resistance properties of the heat-resistant resin with the mechanical strength and porosity of the polyolefin porous film, achieving both heat resistance and mechanical strength simultaneously.

Inventive Principle:

Principle #40Composite materials

2Temperature

If heat-resistant resin is uniformly distributed in the mixed layer, then heat resistance is improved, but flexibility deteriorates

Engineering Contradiction:

Improveheat resistanceVSAvoidflexibility

Core Design Contradiction:

TemperatureVSAdaptability or versatility

Solution Approach 1:

The heat-resistant resin is distributed non-uniformly in the mixed layer, with different concentrations at different positions. This local quality variation allows regions with lower heat-resistant resin concentration to maintain flexibility and adaptability, while regions with higher concentration provide sufficient heat resistance, thus resolving the contradiction between heat resistance and flexibility.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20230318136A1Nonaqueous electrolyte secondary battery separator, nonaqueous electrolyte secondary batter member, and nonaqueous electrolyte secondary battery

Publication Date: 2023.10.05 SUMITOMO CHEM CO LTD

AI summary

As a nonaqueous electrolyte secondary battery separator which has improved mechanical strength and which retains flexibility, provided is a nonaqueous electrolyte secondary battery separator including: a mixed layer which contains a heat-resistant resin and a porous base material that includes a porous film containing a polyolefin-based resin as a main component; and a heat-resistant layer which contains the heat-resistant resin and which is in contact with the mixed layer. When an SEM image which includes a cross section of the nonaqueous electrolyte secondary battery separator in a thickness direction is analyzed, luminance distribution of the mixed layer in the thickness direction satisfies specific conditions.