Battery Separator Stiffness Control for Heat Shrinkage Resistance
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Solution Overview
Problem
Commercial secondary battery separators made of polyolefin exhibit poor heat resistance, significant thermal shrinkage, and are prone to abnormalities like curling, warping, and stretching during production, leading to increased safety risks and reduced reliability.
Innovation Solution
A separator design comprising a first and second base film with a binding layer, where the stiffness in the transverse and machine directions is controlled within specific ranges (1.0-8.0 mN×cm and 1.2-7.0 mN×cm respectively) to maintain regular morphology, reduce short circuits, and enhance mechanical strength and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyolefin is used as separator material, then chemical stability and electrochemical performance are improved, but heat resistance deteriorates and thermal shrinkage increases
Solution Approach 1:
The patent employs a composite structure consisting of a heat-resistant base layer (made from high-temperature resistant polymers like polyimide or polyetheretherketone) and a polyolefin microporous film layer. This composite design allows the separator to maintain the electrochemical performance benefits of polyolefin while the heat-resistant base layer prevents thermal shrinkage and degradation at elevated temperatures, thus resolving the contradiction between electrochemical performance and heat resistance.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the separator by controlling the glass transition temperature (Tg) and melting temperature (Tm) of the base film material to be higher than those of the polyolefin layer. By adjusting these thermal parameters, the separator maintains structural integrity at high temperatures while preserving the electrochemical properties of the polyolefin microporous film, thereby resolving the heat resistance issue without sacrificing electrochemical performance.
2Productivity
If separator stiffness is increased to reduce abnormalities, then production yield is improved, but flexibility deteriorates
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure where different regions of the separator have different mechanical properties. The heat-resistant base layer provides high stiffness and dimensional stability to prevent abnormalities during production, while the polyolefin microporous film layer maintains flexibility and porosity for ion transport. This spatial differentiation of mechanical properties allows the separator to be both stiff enough for high production yield and flexible enough for proper battery operation.
3Reliability
If separator thickness is increased to prevent short circuits, then safety is improved, but energy density deteriorates
Solution Approach 1:
The patent segments the separator into functionally distinct layers: a heat-resistant base layer for dimensional stability and short circuit prevention, and a thin polyolefin microporous film layer for ion transport. This segmentation allows each layer to be optimized for its specific function, achieving adequate safety through the structured multi-layer design rather than simply increasing overall thickness, thus preserving energy density while preventing short circuits.
Data Source
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AI summary
This application provides a separator, a secondary battery, and an electric apparatus. The separator includes a first base film, a second base film, and a binding layer. The binding layer is disposed between the first base film and the second base film. A stiffness of the separator in a transverse direction is denoted as T0, and a stiffness of the separator in a machine direction is denoted as M0, where T0 is 1.0-8.0 mN×cm, and M0 is 1.2-7.0 mN×cm.