Dual-Coated Battery Separator for Breakdown Voltage and Deformation
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Solution Overview
Problem
Existing separators for electrochemical devices, such as lithium secondary batteries, face challenges with low dielectric breakdown voltage, susceptibility to deformation under heat or pressure, and reduced mechanical strength, which compromise battery safety and performance.
Innovation Solution
A separator for electrochemical devices is designed with a porous polymer substrate and two porous coating layers, one with inorganic particles of Mohs hardness 4.5 or less and the other with inorganic particles of Mohs hardness 7 or more, to enhance mechanical strength and resistance to external foreign materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the separator is decreased to increase energy density, then the energy density is improved, but the dielectric breakdown voltage is reduced causing degradation of battery safety
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer combined with inorganic particles (alumina, silica, boehmite) and binder polymers. This composite structure provides both the thin-film characteristics needed for high energy density and the enhanced mechanical strength and dielectric properties required for safety. The inorganic particles reinforce the polymer matrix, preventing deformation while maintaining electrical insulation even at reduced thicknesses.
Solution Approach 2:
The separator employs local quality enhancement by concentrating inorganic particles and binder polymers in specific regions or layers. The coating layers applied to the base layer create zones of enhanced mechanical strength and dielectric properties where they are most needed, allowing the overall separator to be thinner while maintaining safety performance in critical areas.
2Ease of manufacture
If heat and pressure are applied during lamination to assemble the battery, then the assembly is completed, but the dielectric breakdown voltage is reduced causing deformation of the separator
Solution Approach 1:
The separator is pre-reinforced with inorganic particles and binder polymers before the lamination process. This beforehand strengthening creates a cushioning effect that protects the separator from deformation during subsequent heat and pressure application in the lamination process, maintaining its dielectric breakdown voltage and structural integrity throughout manufacturing.
3Device complexity
If a single porous coating layer is used to simplify the structure, then the device complexity is reduced, but the mechanical strength and resistance to deformation are insufficient
Solution Approach 1:
The coating structure is segmented into multiple functional layers: a base polyolefin layer providing porosity and ion transport, and additional coating layers containing inorganic particles and binders providing mechanical reinforcement. This segmentation allows each layer to perform its specific function optimally while working together to achieve overall structural strength and deformation resistance.
Data Source
Figure 1~3
AI summary
The present disclosure relates to a separator and an electrochemical device including the same. The separator includes a porous polymer substrate, a first porous coating layer and a second porous coating layer, wherein a first inorganic particles contained in the first porous coating layer has a lower hardness as compared to a second inorganic particles contained in the second porous coating layer. Since the separator is provided with at least two porous coating layers including inorganic particles having a different hardness, it is possible to increase the dielectric breakdown voltage, and thus to provide a battery with improved safety. It is also possible to reduce deformation of the separator caused by heat or pressure.