Polyethylene Separator Material for Li-Ion Batteries
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Solution Overview
Problem
Polyethylene resins with high molecular weight and narrow molecular weight distribution are needed for separator membranes in batteries to ensure good mechanical properties and processability, but existing high molecular weight polyethylene resins exhibit poor processability due to their high molecular weight.
Innovation Solution
A polyethylene with a melt flow index of 0.4 g/10 min to 0.6 g/10 min, weight average molecular weight of 500,000 g/mol to 700,000 g/mol, and molecular weight distribution of 3 to 5 is prepared using a catalyst that retains at least 50% of its initial reactivity level for over 4 hours, with a Ziegler-Natta catalyst supported on a magnesium compound, and controlled hydrogen input to achieve a small average particle diameter and high crystal relaxation rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyethylene resin with high molecular weight (>1,000,000) is used to achieve high abrasion resistance, high impact resistance, and high chemical resistance, then mechanical strength and durability are improved, but processability deteriorates due to excessively high molecular weight
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight to fall within the range of 500,000 to 700,000 g/mol, which is lower than conventional high molecular weight polyethylene (>1,000,000) but still provides adequate mechanical strength. Additionally, the molecular weight distribution is controlled to be 3 to 5, and melt flow index is adjusted to 0.4 to 0.6 g/10 min, optimizing both mechanical properties and processability for separator membrane fabrication
Solution Approach 2:
The patent employs a composite catalyst system combining Ziegler-Natta catalyst with magnesium support, where the catalyst comprises titanium compound supported on magnesium compound. This composite catalyst structure enables precise control over polymerization kinetics, producing polyethylene with optimized molecular weight and narrow distribution that balances mechanical strength and processability
2Stability of the object's composition
If polyethylene with narrow molecular weight distribution is used to achieve uniform processability and good mechanical properties, then mechanical uniformity is improved, but molecular weight control becomes more difficult
Solution Approach 1:
The patent achieves narrow molecular weight distribution (3 to 5) by controlling polymerization parameters including temperature (0°C to 50°C), pressure (1 to 10 atm), and monomer-to-catalyst ratio. These parameter optimizations enable consistent production of polyethylene with uniform molecular characteristics without requiring overly complex catalyst systems
Solution Approach 2:
The magnesium compound serves as an intermediary support for the titanium catalyst, facilitating controlled polymerization. This intermediary structure provides active sites that promote uniform chain growth, resulting in narrow molecular weight distribution while simplifying the overall catalyst design compared to complex multi-component systems
3Manufacturing precision
If small average particle diameter is achieved to improve uniformity and processability, then processing uniformity is improved, but production efficiency may be reduced
Solution Approach 1:
The patent achieves small average particle diameter (5 to 50 μm) with narrow size distribution by optimizing polymerization parameters including temperature (0°C to 50°C), pressure (1 to 10 atm), and reaction time (1 to 24 hours). These controlled conditions promote uniform nucleation and growth, producing fine particles that enhance processability while maintaining efficient production through continuous polymerization processes
Solution Approach 2:
The patent employs preliminary activation of the Ziegler-Natta catalyst system before main polymerization, where the titanium compound is pre-supported on magnesium compound and activated with organometallic compounds. This preliminary action creates uniform active sites that promote consistent particle formation, achieving small uniform particles without requiring excessively long reaction times or complex multi-stage processes
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 polyethylene exhibits good mechanical properties, uniform processability, and shutdown properties, making it suitable for use in separator membranes, particularly for lithium ion batteries, with optimized molecular weight distribution and particle size.
Implementation Method 1
polymerization in the presence of a catalyst retaining at least about 50% of an initial reactivity level (during the initial 30 minutes) for a period of time exceeding about 4 hours
Implementation Method 2
a titanium compound is supported on a magnesium support
Data Source
AI summary
Disclosed herein is a polyethylene. The polyethylene has a melt flow index of about 0.4 g/10 min to about 0.6 g/10 min, a weight average molecular weight of about 500,000 g/mol to about 700,000 g/mol, and a molecular weight distribution of about 3 to about 5 and is prepared by polymerization in the presence of a catalyst retaining at least about 50% of an initial reactivity level (during initial 30 minutes) for a period of time exceeding about 4 hours.