Calendered Multilayer Battery Separators for Thin Strong Membranes
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Solution Overview
Problem
Current lithium ion battery separators face challenges in achieving thinner, stronger, and more uniform membranes with enhanced performance, particularly in reducing thickness to less than 10 μm for improved energy density and coating adhesion, while maintaining mechanical strength and thermal shutdown functions.
Innovation Solution
A manufacturing process involving machine direction stretching, transverse direction stretching, and subsequent calendering of multilayer polyolefin membranes, specifically polypropylene and polyethylene layers, to reduce thickness, increase tensile strength, and enhance coating adhesion, with the option of biaxial stretching and calendering to achieve a thickness of less than 10 μm and improve surface tension for better coating performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the membrane thickness is reduced to less than 10 μm to improve energy density, then the mechanical strength and structural integrity deteriorate
Solution Approach 1:
The patent employs a multilayer composite structure consisting of a polyethylene layer and a polypropylene layer. The polyethylene layer provides thermal shutdown functionality, while the polypropylene layer contributes mechanical strength and dimensional stability. This composite architecture enables the membrane to achieve thickness below 10 μm while maintaining adequate mechanical properties through the synergistic combination of different polymer materials with complementary characteristics.
Solution Approach 2:
The patent applies different materials and structures to different layers of the membrane to optimize local functions. The polyethylene layer is specifically designed for thermal shutdown at lower temperatures, while the polypropylene layer provides structural support and higher temperature stability. This local differentiation of material properties allows the thin membrane to simultaneously achieve both reduced thickness and maintained mechanical strength through specialized zone design.
2Volume of moving object
If the membrane thickness is reduced to less than 10 μm to improve energy density, then the coating adhesion and surface uniformity deteriorate
Solution Approach 1:
The multilayer composite structure with polyethylene and polypropylene layers provides differentiated surface properties that enhance coating adhesion. The specific layer configuration creates optimal surface characteristics for coating application, ensuring uniform coating distribution and strong adhesion even at reduced thickness below 10 μm.
Solution Approach 2:
The patent utilizes calendering processing to modify physical parameters of the membrane, including surface smoothness, thickness uniformity, and density. By controlling calendering temperature, pressure, and roller speed, the process optimizes surface properties for coating adhesion while maintaining the thin profile required for high energy density applications.
3Strength
If biaxial stretching and calendering are applied to reduce thickness and improve strength, then the process complexity and manufacturing difficulty increase
Solution Approach 1:
The patent combines multiple processing operations into an integrated sequence: extrusion of the multilayer structure, machine direction stretching, transverse direction stretching, and calendering are performed in continuous succession. This merged process flow achieves the desired thin profile and enhanced mechanical properties through cumulative deformation and densification, while maintaining operational efficiency by eliminating separate processing stages.
Solution Approach 2:
The patent systematically adjusts processing parameters throughout the manufacturing sequence to achieve the desired membrane properties. Extrusion temperature, stretching ratios, calendering temperature and pressure are carefully controlled and optimized to produce the target thickness below 10 μm with improved tensile strength and uniformity, managing process complexity through parameter optimization rather than process simplification.
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 process produces membranes with improved mechanical strength, uniformity, and coating adhesion, allowing for higher energy density and rate capability in lithium ion batteries, while maintaining thermal shutdown functionality and reducing the complexity and cost associated with wet process manufacturing.
Implementation Method 1
a subsequent calendering step as a possibly preferred means to reduce the thickness of such a stretched membrane, for example, a multilayer porous membrane, in a controlled manner
Implementation Method 2
calendering step as a possibly preferred means to reduce the thickness
Implementation Method 3
machine direction stretching followed by transverse direction stretching
Data Source
AI summary
Novel or improved microporous single or multilayer battery separator membranes, separators, batteries including such membranes or separators, methods of making such membranes, separators, and/or batteries, and/or methods of using such membranes, separators and/or batteries are provided. In accordance with at least certain embodiments, a multilayer dry process polyethylene/polypropylene/polyethylene microporous separator which is manufactured using the inventive process which includes machine direction stretching followed by transverse direction stretching and a subsequent calendering step as a means to reduce the thickness of the multilayer microporous membrane, to reduce the percent porosity of the multilayer microporous membrane in a controlled manner and/or to improve transverse direction tensile strength. In a very particular embodiment, the inventive process produces a thin multilayer microporous membrane that is easily coated with polymeric-ceramic coatings, has excellent mechanical strength properties due to its polypropylene layer or layers and a thermal shutdown function due to its polyethylene layer or layers. The ratio of the thickness of the polypropylene and polyethylene layers in the inventive multilayer microporous membrane can be tailored to balance mechanical strength and thermal shutdown properties.