Calendered Multilayer Battery Separators for Thin Strength Balance
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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
1Quantity of substance
If the membrane thickness is reduced to less than 10 μm to improve energy density, then the energy density increases, but the mechanical strength decreases
Solution Approach 1:
The patent employs a multilayer composite structure consisting of polyethylene layers and polypropylene layers. The polyethylene layers provide thermal shutdown function while the polypropylene layers provide mechanical strength. This composite approach allows the membrane to achieve thickness less than 10 μm while maintaining adequate mechanical strength through the synergistic combination of different materials with complementary properties.
2Strength
If transverse direction stretching and calendering are applied to increase tensile strength, then the transverse direction tensile strength increases, but the process complexity increases
Solution Approach 1:
The multilayer nonporous membrane structure is prepared in advance through extrusion and lamination before the stretching and calendering operations. This preliminary structuring provides a stable base that can withstand the subsequent mechanical processing. The machine direction stretching is performed first to establish the basic pore structure, followed by transverse direction stretching and calendering to fine-tune the properties. This sequential preliminary action simplifies the overall process by preparing the material in optimal stages.
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 thinner, stronger, and more uniform battery separators with improved transverse direction tensile strength, thermal shutdown capabilities, and enhanced coating adhesion, allowing for higher energy density and higher rate capability batteries without the complexities and costs associated with wet process manufacturing.
Implementation Method 1
machine direction stretching, transverse direction stretching
Implementation Method 2
subsequent calendering step... to reduce the thickness of such a stretched membrane, reduce the percent porosity
Implementation Method 3
The calendering process may use heat, pressure and speed to densify a heat sensitive material
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.