Battery Separator Mixed Layer for Heat Resistance and Ion Permeability
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Solution Overview
Problem
Conventional nonaqueous electrolyte secondary battery separators exhibit insufficient heat resistance, particularly in low weight per unit area regions, and have room for improvement in ion permeability and resistance maintaining properties.
Innovation Solution
A nonaqueous electrolyte secondary battery separator is developed with a mixed layer containing a heat-resistant resin and a porous base material, where the weight ratio of the heat-resistant resin to the porous base material is not less than 0.07, enhancing the penetration of the heat-resistant resin into the porous film, and optionally including a heat-resistant layer with a filler.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the degree of penetration of the heat-resistant resin into the porous film is increased, then the heat resistance is improved, but the ion permeability and resistance are predicted to deteriorate
Solution Approach 1:
The invention changes the penetration parameter to a specific range (weight ratio W1/W0 of 0.03 to 0.20) to optimize the balance between heat resistance and ion permeability. This parameter optimization resolves the contradiction by finding the sweet spot where sufficient resin penetration provides heat resistance while maintaining adequate ion transport pathways.
Solution Approach 2:
The invention creates a composite structure combining heat-resistant resin with porous base material (polyolefin or aramid). This composite approach allows the separator to simultaneously exhibit heat resistance from the resin and ion permeability from the porous structure, resolving the contradiction between these two properties.
2Weight of moving object
If the weight per unit area of the separator is reduced, then the battery performance is improved, but the heat resistance becomes insufficient
Solution Approach 1:
The invention optimizes the weight ratio parameter (W1/W0 between 0.03 to 0.20) to achieve maximum heat resistance efficiency per unit weight. By controlling the penetration degree within this specific range, the separator achieves sufficient heat resistance with minimal resin content, thus maintaining low weight per unit area while improving heat resistance.
Solution Approach 2:
The heat-resistant resin is locally distributed within the porous film structure rather than uniformly distributed. This local penetration approach provides heat resistance precisely where needed (at the pore walls and interfaces) while minimizing the overall resin content and maintaining low weight per unit area.
3Reliability
If the degree of penetration of the heat-resistant resin is suppressed, then the shutdown characteristic is maintained, but the heat resistance is insufficient particularly in low weight per unit area regions
Solution Approach 1:
The invention identifies and controls the penetration parameter (weight ratio W1/W0) within the optimal range of 0.03 to 0.20. This parameter control ensures that the resin penetration is sufficient to provide heat resistance but not excessive to compromise shutdown characteristics, resolving the contradiction between these two requirements.
Solution Approach 2:
The invention utilizes the porous structure of the base material to allow controlled resin penetration. The porous architecture enables the resin to penetrate to the extent needed for heat resistance while preserving the pore pathways necessary for shutdown function, thus resolving the contradiction between heat resistance and shutdown characteristic.
Data Source
AI summary
As a nonaqueous electrolyte secondary battery separator which has excellent heat resistance and excellent battery performance, 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 polyolefin porous film, in the mixed layer, a weight ratio (W1/W0) between a weight W1 of the heat-resistant resin and a weight W0 of the porous base material being not less than 0.07.