Three-Layer Separator Thermal Expansion Puncture Strength
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries require separators with increased puncture strength to prevent internal short circuits caused by conductive contaminants, while also achieving reduced thickness and higher porosity for enhanced capacity and power.
Innovation Solution
A separator with a three-layer structure consisting of an A-layer, a B-layer, and a C-layer, where the average thermal expansion coefficient of the A-layer and C-layer is 100 ppm/K or more less than that of the B-layer, providing increased puncture strength by generating compressive stress and preventing cracks from contaminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If separator thickness is reduced to achieve high capacity, then battery capacity increases, but separator strength decreases leading to potential internal short circuits
Solution Approach 1:
The separator is divided into multiple functional layers: a base layer (polypropylene or polyethylene) providing structural support and puncture strength, and a porous coating layer providing ionic permeability. This segmentation allows each layer to optimize for its specific function while maintaining overall separator strength even at reduced thickness.
Solution Approach 2:
The separator uses composite material structure combining different polymers (polypropylene base layer with polyethylene coating, or vice versa) to achieve both mechanical strength and ionic conductivity. The composite structure enables the thin separator to maintain high puncture strength while providing sufficient porosity for ion transport.
2Quantity of substance
If porosity is increased to achieve high capacity, then ionic permeability improves, but structural integrity and puncture strength decrease
Solution Approach 1:
Different regions of the separator have different properties: the base layer has high mechanical strength with moderate porosity, while the porous coating layer has high porosity for ionic permeability but relies on the base layer for structural support. This local differentiation allows the separator to achieve high overall porosity without compromising puncture strength.
Solution Approach 2:
The separator structure separates the functions of mechanical support and ionic transport into distinct layers, allowing the porous coating layer to achieve high porosity (50-80%) for excellent ionic permeability while the base layer maintains structural integrity and puncture strength.
3Ease of manufacture
If a single-layer separator structure is used to simplify manufacturing, then manufacturing complexity decreases, but it is difficult to achieve both high strength and high porosity simultaneously
Solution Approach 1:
The invention combines multiple functional requirements into a integrated two-layer structure where the base layer and porous coating layer work together. This merging of functions (structural support + ionic transport) into a single composite component achieves both high strength and high porosity simultaneously, while the lamination process remains relatively simple and compatible with existing manufacturing methods.
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 three-layer separator structure ensures high puncture strength, allowing for reduced thickness and increased porosity, effectively inhibiting contaminant penetration and preventing internal short circuits in nonaqueous electrolyte secondary batteries.
Implementation Method 1
The average thermal expansion coefficient of the A-layer at a temperature of 0° C. to 50° C. is 100 ppm/K or more less than the average thermal expansion coefficient of the B-layer at a temperature of 0° C. to 50° C. The average thermal expansion coefficient of the C-layer at a temperature of 0° C. to 50° C. is 100 ppm/K or more less than the average thermal expansion coefficient of the B-layer at a temperature of 0° C. to 50° C.
Data Source
AI summary
A nonaqueous electrolyte secondary battery includes an electrode assembly including a positive electrode, a negative electrode, and a separator and a nonaqueous electrolyte. The separator includes a porous resin sheet having at least a three-layer structure consisting of an A-layer, a B-layer, and a C-layer stacked in that order. The average thermal expansion coefficient of each of the A-layer and the C-layer at a temperature of 0° C. to 50° C. is 100 ppm/K or more less than the average thermal expansion coefficient of the B-layer at a temperature of 0° C. to 50° C.