Co-Extruded Microlayer Battery Separators for Split Resistance
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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, leading to issues such as splitting and reduced dielectric breakdown strength.
Innovation Solution
The development of novel, multi-layered microporous membranes created through co-extrusion and lamination techniques, featuring multiple layers of polyethylene and polypropylene, which are laminated together to enhance strength and reduce splitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If single-layer or simple multi-layer membranes are used, then manufacturing is simpler, but strength and resistance to splitting are insufficient
Solution Approach 1:
The membrane is divided into multiple distinct layers (typically 3-5 layers) with different polymer compositions and pore structures. Each layer serves specific functions: outer layers provide mechanical strength and split resistance, while inner layers provide porosity and ion transport. This segmentation allows optimization of each layer's properties to achieve overall high strength without excessive complexity.
Solution Approach 2:
The invention uses composite membrane structures combining different polymer materials (e.g., polyolefin, polyester, polyacrylonitrile) in a multi-layer configuration. Each polymer contributes different properties: some provide strength, others provide porosity or chemical stability. The composite structure achieves superior mechanical strength and split resistance that cannot be obtained with single-material membranes.
2Strength
If membrane thickness is increased to improve strength, then mechanical strength improves, but dielectric breakdown strength and ion transport performance deteriorate
Solution Approach 1:
Instead of using a single thick membrane layer, the invention segments the thickness into multiple thin layers (each 1-10 micrometers). The total thickness is maintained or reduced, but the multi-layer architecture provides enhanced mechanical strength through distributed stress across multiple interfaces. Each thin layer maintains adequate porosity for ion transport and dielectric breakdown strength.
Solution Approach 2:
Different layers have different local properties optimized for their specific functions. Outer layers may have higher density and lower porosity for mechanical strength, while inner layers have higher porosity for ion transport. This local optimization allows the membrane to achieve high mechanical strength without compromising dielectric breakdown strength or ion transport, as each region contributes its specialized property.
3Productivity
If membrane porosity is increased to improve ion transport, then ion transport performance improves, but mechanical strength and resistance to splitting deteriorate
Solution Approach 1:
The membrane is segmented into layers with different porosity levels. Inner layers have high porosity (40-60%) to facilitate ion transport, while outer layers have lower porosity (20-40%) to provide mechanical strength and split resistance. This segmentation allows the membrane to achieve high ion transport rates through the porous inner layers while the denser outer layers prevent mechanical failure and splitting.
Solution Approach 2:
Each layer has locally optimized porosity matching its functional requirements. The high-porosity regions are confined to inner transport layers where ion flow is needed, while low-porosity regions are placed in outer structural layers where mechanical strength is needed. This local quality differentiation resolves the contradiction between ion transport performance and mechanical strength.
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.