Composite Battery Separator for Thin-Film Breakdown Resistance
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Solution Overview
Problem
Existing separators for electrochemical devices, particularly lithium ion batteries, face challenges in achieving a balance between thin film thickness for increased energy density, mechanical strength, and insulation properties while minimizing the risk of short-circuit generation and ensuring high breakdown voltage.
Innovation Solution
A separator comprising a porous polymer substrate with a heat-resistant layer containing inorganic particles and a binder resin, which provides excellent compressibility, permanent strain, and improved physical strength, reducing the likelihood of short-circuits and enhancing voltage resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the separator thickness is reduced to increase energy density, then the energy density is improved, but the mechanical strength and insulation properties deteriorate
Solution Approach 1:
The patent employs a composite structure consisting of a polyethylene microporous membrane combined with a heat-resistant layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder resin. This composite design allows the separator to maintain thin dimensions for high energy density while the heat-resistant layer provides enhanced mechanical strength, thermal stability, and insulation properties, preventing short-circuits even at reduced thickness
2Temperature
If a polypropylene microporous membrane is used to achieve high shutdown temperature, then the shutdown temperature is improved, but the permeability and penetration strength deteriorate
Solution Approach 1:
The patent divides the separator into two functional segments: a polyethylene microporous membrane base layer providing good permeability and ion transport, and a separate heat-resistant layer containing inorganic particles providing high-temperature stability. This segmentation allows each layer to optimize its specific function without compromising the other, achieving both high shutdown temperature and good permeability
Solution Approach 2:
The heat-resistant layer is applied locally on the polyethylene microporous membrane, creating a layered structure where the polyethylene layer maintains permeability and the heat-resistant layer provides thermal stability. This local quality differentiation allows the separator to exhibit both high shutdown temperature and good penetration strength simultaneously
3Use of energy by moving object
If the separator is made thinner to increase energy density, then the energy density is improved, but the breakdown voltage and short-circuit resistance deteriorate
Solution Approach 1:
The composite structure with inorganic particles in the heat-resistant layer provides enhanced electrical insulation and breakdown voltage resistance even at thin dimensions, preventing short-circuits while maintaining high energy density
Data Source
Figure 1
AI summary
Provided is a separator for an electrochemical device. The separator includes a porous substrate made of a porous polymer film having an excellent compressibility and permanent strain, wherein the porous substrate has excellent physical strength and durability and ensures a high breakdown voltage while using a heat resistant layer having a small thickness, and thus shows a low possibility of short-circuit generation. In addition, the separator may further include a heat resistant layer including inorganic particles, on the surface of the porous substrate. Herein, it is possible to further improve the compressibility, maximum compressibility and permanent strain characteristics depending on types of inorganic particles.