Thin Polyethylene Separator for High Breakdown Voltage Batteries
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Solution Overview
Problem
Current 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 combining polyethylene base resin with polypropylene particles (5-50 wt%). This composite material configuration allows the thin separator (5-20 μm) to achieve both high mechanical strength and high breakdown voltage (75 V or more) while maintaining reduced thickness for improved energy density.
2Strength
If the porosity is reduced to improve mechanical strength, then the mechanical strength is improved, but the permeability deteriorates
Solution Approach 1:
The patent optimizes the porosity parameter to 30-45%, finding the optimal balance point where mechanical strength is sufficiently improved while ion permeability remains adequate for battery operation. This parameter optimization resolves the contradiction between strength and permeability.
3Strength
If the polyethylene molecular weight is increased to improve mechanical strength, then the mechanical strength is improved, but the processing difficulty increases
Solution Approach 1:
The patent specifies a weight average molecular weight range of 300,000 to 1,000,000 for polyethylene, optimizing this parameter to achieve high mechanical strength while maintaining processability. This controlled molecular weight parameter allows strong separator films to be manufactured with reasonable processing difficulty.
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.