Composite Porous Separator for Lithium Battery Heat Resistance
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Solution Overview
Problem
Lithium secondary battery separators face challenges in achieving thinness while maintaining heat resistance and mechanical strength, as thin ceramic-coated separators suffer from increased moisture content and curling issues, leading to reduced battery lifespan and capacity.
Innovation Solution
A composite porous separator with a coating layer containing two or more kinds of inorganic particles of different sizes and a polymer binder with a glass transition temperature of 100°C to 200°C, applied to one or both surfaces of a porous substrate, enhancing heat resistance and mechanical strength while minimizing moisture content and curling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the coating layer and porous substrate are made thinner to achieve a thinner separator, then the lifespan of the lithium secondary battery is improved, but the density of inorganic particles in the coating layer is reduced, causing deterioration of heat resistance
Solution Approach 1:
The patent uses a composite coating layer comprising inorganic particles (such as alumina, boehmite, or silica) dispersed in a polymer binder matrix. This composite structure allows the coating to maintain heat resistance through the inorganic particles while achieving thinness through the polymer matrix, resolving the contradiction between thickness reduction and heat resistance maintenance
Solution Approach 2:
The patent optimizes parameters including the weight ratio of inorganic particles to binder (95:5 to 99:1), particle size distribution (0.1-10 μm), and coating thickness (1-20 μm) to achieve the desired balance between thinness and heat resistance. By carefully controlling these parameters, the coating maintains sufficient heat resistance even at thin dimensions
2Strength
If a high-strength porous substrate is selected to suppress deterioration of mechanical properties when using a thin substrate, then mechanical strength is improved, but the shrinking force of the substrate is larger than that of the coating layer, resulting in an increase in the occurrence of curls
Solution Approach 1:
The patent applies different materials and properties to different parts of the separator structure. The porous substrate uses high-strength materials (polyethylene, polypropylene, or their copolymers) for mechanical strength, while the coating layer uses materials with complementary shrinkage characteristics. This local differentiation of material properties allows each layer to perform its primary function without causing curling
Solution Approach 2:
The patent controls the shrinkage forces by selecting substrates with specific shrinkage rates (5-20% at 100°C) and matching them with coating layers having complementary shrinkage characteristics. By optimizing the thickness ratio (coating layer 1-20 μm, substrate 10-50 μm) and shrinkage parameters, the patent achieves mechanical strength without excessive curling
3Reliability
If a ceramic-coated separator is used to provide heat resistance and suppress shrinkage, then heat resistance is improved, but it is difficult to achieve the thinness required to improve battery lifespan
Solution Approach 1:
The patent employs a porous substrate with controlled porosity (30-70%) as the base structure. This porous architecture provides mechanical strength and electrolyte penetration pathways while maintaining thinness. The porous structure allows the separator to achieve the required thin dimensions without sacrificing mechanical integrity
Solution Approach 2:
The patent creates a composite structure where a thin porous substrate (10-50 μm) is combined with an inorganic particle coating layer (1-20 μm). This composite design achieves both thinness (for improved lifespan) and heat resistance (through inorganic particles), resolving the contradiction between these two requirements
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 solution results in a separator with improved heat resistance, reduced heat shrinkage rate, and low moisture content, thereby extending battery lifespan and stability, and enabling the production of high-capacity energy storage devices with enhanced performance.
Implementation Method 1
the binder contains a polymer having a glass transition temperature (Tg) of 100°C to 200°C
Data Source
Figure 1(a)~1(b)
AI summary
The present invention relates to a composite porous separator, a method of manufacturing the same, and an electrochemical device including the same. Provided is a porous substrate that has excellent heat resistance and heat shrinking properties, a small thickness, and high strength even when a thickness of a coating layer containing inorganic particles is small. Provided are a composite porous separator having significantly reduced heat shrinking and curls according to the present invention, and an electrochemical device using the same.