Microlayer Battery Separators for Strength and Shutdown Balance
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Solution Overview
Problem
Existing battery separator membranes lack optimal balance of strength and performance properties, particularly in lithium ion rechargeable batteries, with issues related to splitting, tensile strength, and dielectric breakdown.
Innovation Solution
Development of multi-layered microporous membranes created through co-extrusion and lamination of polyethylene and polypropylene layers, with each layer being micrometer or nanometer thick, forming constructions like [PE/PE/PE]/PP/[PE/PE/PE] to enhance mechanical strength, porosity, and reduced splitting tendency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional single-layer or simple multi-layer membranes are used, then manufacturing is simpler, but mechanical strength and resistance to splitting are insufficient
Solution Approach 1:
The membrane is divided into multiple thin layers (microlayers) of different polymers, each contributing specific mechanical properties. The segmented multi-layer structure distributes stress across layers, preventing catastrophic failure and improving overall mechanical strength while maintaining manufacturability through sequential lamination of pre-formed layers.
Solution Approach 2:
The invention uses composite materials by combining different polymers (e.g., polyethylene and polypropylene) in a multi-layer configuration. Each polymer contributes distinct mechanical characteristics, and their combination creates a composite membrane with superior strength-to-weight ratio and enhanced resistance to splitting compared to single-layer membranes.
2Quantity of substance
If membrane thickness is reduced to improve battery energy density, then battery capacity increases, but dielectric breakdown strength decreases
Solution Approach 1:
The multi-layer composite structure maintains dielectric breakdown strength at reduced thickness by distributing the electrical stress across multiple layers with different dielectric properties. The alternating polymer layers create a composite dielectric barrier that prevents breakdown at lower overall thickness than single-layer membranes would require.
Solution Approach 2:
Instead of reducing thickness in one dimension, the invention uses multiple thin layers stacked in the thickness direction, effectively using the layering dimension to maintain dielectric performance. The multi-layer architecture provides cumulative dielectric strength equivalent to thicker single-layer membranes while enabling thinner overall construction.
3Quantity of substance
If membrane thickness is reduced to improve battery energy density, then battery capacity increases, but mechanical strength decreases
Solution Approach 1:
The membrane is segmented into multiple thin layers, each contributing to the overall mechanical strength. This segmentation allows the total thickness to be reduced while maintaining strength, as each layer bears a portion of the mechanical load and the layered structure prevents crack propagation that would occur in thin single-layer membranes.
Solution Approach 2:
The composite multi-layer structure provides enhanced mechanical strength at reduced thickness by combining polymers with complementary mechanical properties. The different polymer layers work together to distribute mechanical stresses, preventing failure modes that would occur in thinner single-layer membranes.
4Productivity
If porosity is increased to improve ion transport, then battery performance improves, but mechanical strength decreases
Solution Approach 1:
The multi-layer composite structure balances porosity and strength by having layers with different pore structures. Some layers are designed with higher porosity to facilitate ion transport, while alternating layers provide mechanical support with lower porosity. This composite approach allows high overall ion transport efficiency while maintaining adequate mechanical strength through the supporting layers.
Data Source
AI summary
In accordance with at least selected embodiments, a battery separator or separator membrane comprises one or more co-extruded multi-microlayer membranes optionally laminated or adhered to another polymer membrane. The separators described herein may provide improved strength, for example, improved puncture strength, particularly at a certain thickness, and may exhibit improved shutdown and/or a reduced propensity to split.