Composite Battery Separator Stiffness for Heat and Shape Stability
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Solution Overview
Problem
Commercial secondary battery separators exhibit poor heat resistance, thermal shrinkage, and are prone to curling, warping, wrinkling, and stretching during production, leading to increased safety risks and reduced reliability due to potential short circuits between the positive and negative electrodes.
Innovation Solution
A separator design comprising a first and second base film with a binding layer, where the stiffness in the transverse direction (T0) is 1.0-8.0 mN×cm and in the machine direction (M0) is 1.2-7.0 mN×cm, enhancing mechanical strength and heat resistance, and controlling separator size to prevent local shrinkage and dendrite penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional separators are used, then production cost is low, but heat resistance is poor and thermal shrinkage occurs
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base film combined with a heat-resistant ceramic coating layer. This composite structure provides both the functional properties of the base film and the thermal stability of the ceramic layer, resolving the contradiction between low cost and heat resistance.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the separator by controlling the crystallinity, melting point, and thermal expansion coefficients of the materials used. These parameter changes enable the separator to maintain dimensional stability at elevated temperatures while retaining cost-effectiveness.
2Ease of manufacture
If conventional separators are used, then manufacturing is simple, but curling, warping, wrinkling, and stretching occur during production
Solution Approach 1:
The patent optimizes manufacturing parameters including stretching ratios, heating temperatures, and cooling rates to control the separator's mechanical properties. By adjusting these parameters, the separator achieves appropriate stiffness and dimensional stability that prevents deformation during production while maintaining ease of manufacture.
Solution Approach 2:
The separator undergoes preliminary heat treatment and mechanical conditioning during manufacturing to pre-establish its dimensional stability. This preliminary action ensures that the separator resists curling, warping, and wrinkling during subsequent production processes without complicating the manufacturing workflow.
3Manufacturing precision
If separator stiffness is increased to prevent deformation, then morphology stability improves, but dendrite penetration resistance decreases
Solution Approach 1:
The patent applies different material properties to different regions and aspects of the separator. The base film provides mechanical stiffness for morphology stability, while the ceramic coating layer provides dendrite penetration resistance. This local differentiation of material functions resolves the contradiction between stiffness and penetration resistance.
Solution Approach 2:
The composite structure allows the base film to provide dimensional stability and the ceramic coating to provide dendrite resistance. This multi-functional composite material simultaneously achieves morphology stability and penetration resistance without requiring increased overall stiffness.
4Temperature
If separator thickness is increased to improve mechanical strength, then heat resistance improves, but production yield decreases due to size control issues
Solution Approach 1:
The patent changes the material composition parameters to achieve high heat resistance in a thin separator structure. By using materials with high melting points and low thermal expansion, the separator achieves superior heat resistance without increasing thickness, thereby maintaining production yield.
Solution Approach 2:
The ceramic-coated composite structure provides enhanced heat resistance with minimal thickness increase. The coating layer contributes thermal stability while adding negligible thickness, allowing the separator to achieve high heat resistance without the size control issues associated with thicker separators.
Data Source
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.