UHMWPE Microporous Membrane Blend for Thin Battery Separators
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Solution Overview
Problem
There is a need for microporous membranes with reduced thickness while maintaining or increasing strength, particularly for battery separators in secondary lithium ion batteries.
Innovation Solution
A microporous sheet made from a blend of two ultra high molecular weight polyethylenes with different molecular weights, where the intrinsic viscosity is greater than or equal to 6.3, and the membrane is manufactured using a wet process involving a blend of resin components and processing oil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of the separator is decreased to reduce weight and improve performance, then the strength (puncture strength) deteriorates
Solution Approach 1:
The patent applies composite materials by blending two different UHMW polyethylene resins with distinct molecular weights and viscosity characteristics. The first resin (higher viscosity) provides structural integrity and puncture strength, while the second resin (lower viscosity) enhances processability and membrane formation. This composite approach enables the production of ultra-thin separators (15-30 micrometers) that maintain adequate mechanical strength through synergistic material properties rather than relying on thickness alone.
Solution Approach 2:
The patent utilizes parameter changes by carefully controlling the molecular weight distribution and viscosity ratio of the blended polyethylene resins. By adjusting the blend composition and processing parameters (extrusion temperature, cooling rate, orientation conditions), the patent achieves optimal balance between thinness and strength. The intrinsic viscosity ratio and molecular weight differences are precisely controlled to enable membrane formation at reduced thickness while maintaining puncture resistance through enhanced molecular chain entanglement and crystalline structure.
2Reliability
If the wet process is used to manufacture UHMWPE membranes, then the membrane quality improves, but the process complexity increases due to solvent extraction requirements
Solution Approach 1:
The patent applies parameter changes by optimizing the resin blend composition and processing conditions to enhance membrane quality through controlled phase separation and crystallization during the wet process. By adjusting the molecular weight distribution and viscosity ratio of the blended polyethylene resins, the patent achieves superior membrane uniformity, pore structure, and mechanical properties.
3Ease of manufacture
If a single UHMWPE resin is used, then the manufacturing process is simple, but the membrane performance is limited
Solution Approach 1:
The patent applies composite materials by blending two different UHMW polyethylene resins with distinct molecular weights and viscosity characteristics. The first resin (higher viscosity) provides structural integrity and puncture strength, while the second resin (lower viscosity) enhances processability and membrane formation. This composite approach enables the production of ultra-thin separators (15-30 micrometers) that maintain adequate mechanical strength through synergistic material properties rather than relying on thickness alone.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting membrane has improved puncture strength, porosity, and average pore size, making it suitable for applications requiring enhanced performance and reduced thickness.
Implementation Method 1
The wet process, typically, includes one of the following phase separation mechanisms: (1) liquid-liquid phase separation; or (2) solid-liquid phase separation.
Implementation Method 2
The solid-liquid phase separation, also known as GEL process, refers to polymer crystallization from a melt blend.
Implementation Method 3
The wet process involves mixing of a polyolefin resin with a hydrocarbon liquid or some other low molecular weight substance
Implementation Method 4
heating and melting the mixture, extruding the melt into a sheet
Implementation Method 5
extruding the melt into a sheet
Implementation Method 6
orienting (or stretching) the sheet to form micropores
Data Source
AI summary
A membrane is a microporous sheet made of a blend of a first ultra high molecular weight polyolefin and a second ultra high molecular weight polyolefin. Each polyolefin has a molecular weight, both of those molecular weights are greater than 1 million, and one molecular weight is greater than the other. Additionally, the intrinsic viscosity (IV) of the membrane may be greater than or equal to 6.3.