Thin Polyethylene Separator Structure for High Breakdown Voltage
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Solution Overview
Problem
Existing separators for electrochemical devices, particularly lithium-ion batteries, face challenges in achieving high breakdown voltage and preventing short-circuit generation due to limitations in mechanical strength, permeability, and thickness, which affect battery safety and energy density.
Innovation Solution
A separator with a porous substrate made of polyethylene, having a weight average molecular weight of 300,000 to 1,000,000, and a thickness of 5 μm to 20 μm, with a porosity of 45% or less and compressibility of 15% or less, optionally including polypropylene up to 5 wt%, and a heat-resistant layer with inorganic particles, to enhance mechanical strength and voltage resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the separator thickness is reduced to increase energy density, then the energy density is improved, but the mechanical strength and voltage resistance deteriorate
Solution Approach 1:
The separator uses a composite structure consisting of a polyethylene microporous membrane as the base layer and a polypropylene microporous membrane as the heat-resistant layer. This composite structure allows the thin separator to maintain both mechanical strength and voltage resistance while achieving reduced thickness for higher energy density.
2Productivity
If the porosity is increased to improve permeability, then the permeability is improved, but the mechanical strength and insulation property deteriorate
Solution Approach 1:
The patent optimizes the porosity parameter to be 30% or less, balancing permeability requirements with mechanical strength and insulation properties. The controlled porosity ensures adequate ion transport while maintaining structural integrity and electrical insulation.
3Reliability
If polypropylene is used to improve thermal shrinking resistance, then the thermal shrinking resistance is improved, but the shutdown temperature becomes too high and permeability decreases
Solution Approach 1:
The separator is divided into functional segments: a polyethylene layer providing shutdown function at lower temperatures (melting point 100-140°C) and a polypropylene layer providing thermal shrinking resistance at higher temperatures. This segmentation allows each material to perform its optimal function without compromising overall performance.
4Quantity of substance
If a thin film structure is used to increase energy density, then the energy density is improved, but the insulation property and mechanical strength deteriorate
Solution Approach 1:
The thin film separator combines polyethylene and polypropylene in a composite structure, where the polypropylene component provides enhanced insulation properties and mechanical strength, enabling the separator to be thin while maintaining adequate insulation performance.
Data Source
AI summary
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. 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. It is possible to further improve the compressibility, maximum compressibility and permanent strain characteristics depending on the types of inorganic particles.