UHMWPE Battery Separator Casting for High Strength and Pore Control
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Solution Overview
Problem
Current methods for producing polyolefin microporous membranes using ultrahigh molecular weight polyethylene (UHMWPE) face challenges in achieving high quality, including low gelling, molecular weight degradation, and reduced separator strength for lithium ion batteries, such as tensile and puncture strength.
Innovation Solution
A method involving a mixed slurry of liquid plasticizer and UHMWPE is used for extrusion and casting, with specific conditions based on X-ray diffraction to control crystallinity and pore formation, resulting in a separator with a cross-sectional crystal orientation of 0.85 or greater, specific surface area of 1×10−2 nm2 to 5×10−2 nm2, and equivalent mean pore size of 50 nm to 150 nm, enhancing mechanical strength and compression resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultrahigh molecular weight polyethylene (UHMWPE) is used to produce polyolefin microporous membranes, then separator strength including tensile strength and puncture strength is improved, but manufacturing difficulty increases due to casting challenges and gelling issues
Solution Approach 1:
The patent introduces a lubricant as an intermediary substance to facilitate the casting of UHMWPE. The lubricant forms a slurry with the polymer powder, enabling smooth extrusion and casting without direct contact between the high-friction UHMWPE and the equipment surfaces, thereby resolving the manufacturing difficulty while maintaining the use of high molecular weight polymer for strength
Solution Approach 2:
The patent changes the physical state and processing parameters by converting UHMWPE powder into a slurry mixture with lubricant. This parameter change allows the material to be processed at lower temperatures and with reduced shear stress, preventing gelling and molecular weight degradation while enabling successful casting
2Stability of the object's composition
If melt kneading is used to process polyolefin resin, then homogeneous mixing is achieved, but molecular weight degradation occurs due to high shear stress and heat
Solution Approach 1:
The patent replaces the conventional melt kneading mechanical process with a slurry-based mixing approach. Instead of using high-shear mechanical kneading that degrades molecular weight, the method uses lubricant-mediated slurry formation followed by gentle drying, achieving homogeneous mixing without excessive mechanical stress or heat generation
Solution Approach 2:
The lubricant acts as a mediator that enables homogeneous distribution of polymer particles without requiring high-shear mechanical mixing. The lubricant coats and separates individual polymer particles, allowing uniform dispersion to be achieved through gentle mixing processes that preserve molecular weight
3Strength
If high crystallinity is achieved in the separator, then mechanical strength and compression resistance are improved, but pore formation becomes more difficult
Solution Approach 1:
The patent performs preliminary pore formation by extracting lubricant from the cast membrane before the crystallization process. This preliminary action creates the porous structure first, and then the subsequent heat treatment promotes crystallinity within the already-formed pores, allowing both high crystallinity and good pore structure to coexist without conflict
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 approach results in a high-quality separator with improved tensile strength, puncture resistance, and compression resistance, addressing the limitations of existing technologies by maintaining membrane integrity during battery operation and extending battery lifespan.
Implementation Method 1
a method involving a mixed slurry of liquid plasticizer and UHMWPE is used for extrusion and casting, with specific conditions based on X-ray diffraction to control crystallinity
Implementation Method 2
specific conditions based on X-ray diffraction to control crystallinity
Data Source
AI summary
A separator for an electricity storage device has a cross-sectional crystal orientation of 0.85 or greater, and/or a method for producing the separator for an electricity storage device comprises a step of using a continuous mixer under conditions with a temperature of 20° C. to 70° C., a shear rate of 100 to 400,000 seconds−1 and a residence time of 1.0 seconds to 60 seconds, for mixing of polyethylene-containing polyolefin powder with a plasticizer to produce a mixed slurry, a step of extruding the mixed slurry and cooling it to solidification to process it into a cast sheet, and a step of biaxially stretching the cast sheet to an area increase factor of 20 to 200.