Polyethylene Microporous Membrane Planarity Control
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Solution Overview
Problem
Polyolefin microporous membranes used as battery separators often suffer from waviness during production, leading to poor planarity and defects in coating layers, which compromises their performance and safety.
Innovation Solution
A polyethylene microporous membrane with improved planarity is produced through a process involving heat-dissolving polyethylene in a solvent, extruding, cooling, stretching, solvent removal, and heat-relaxing, resulting in a membrane with Gurley air permeability of 1 to 1,000 sec/100 mL/25 µm and porosity of 15 to 85%, allowing for uniform coating and enhanced safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyolefin microporous membrane is used as battery separator, then good permeability and strength are achieved, but waviness occurs during production leading to poor planarity
Solution Approach 1:
The patent applies parameter changes by controlling the molecular weight of polyethylene (5×10^5 to 5×10^6) and adjusting processing parameters during membrane formation to minimize waviness while maintaining permeability and strength. This resolves the contradiction by optimizing physical parameters to achieve both reliability and manufacturing precision.
Solution Approach 2:
The patent uses composite material structure by combining polyethylene with specific molecular weight characteristics and incorporating it into a microporous membrane structure. This composite approach enables the membrane to simultaneously achieve good mechanical strength, permeability, and planarity, resolving the technical contradiction between reliability and manufacturing precision.
2Reliability
If coating layer is formed on microporous membrane, then shutdown function and heat resistance are improved, but coating defects occur due to poor planarity
Solution Approach 1:
The patent applies preliminary action by ensuring high planarity of the microporous membrane substrate before the coating process. By pre-controlling the membrane formation to minimize waviness, the subsequent coating operation can proceed uniformly without defects, thus achieving both improved reliability through coating and manufacturing precision in coating uniformity.
3Area of stationary object
If large microporous membrane is produced for big batteries, then battery size requirements are met, but thickness irregularities and planarity issues increase
Solution Approach 1:
The patent applies parameter changes by optimizing the polyethylene molecular weight range (5×10^5 to 5×10^6) and controlling processing parameters during large-area membrane production. This enables the manufacture of large-sized membranes while maintaining uniform thickness and good planarity, resolving the contradiction between membrane area and manufacturing precision.
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 membrane exhibits excellent permeability, planarity, and absorbency, reducing the likelihood of coating defects and improving the safety and functionality of batteries as separators.
Implementation Method 1
cooling, stretching, solvent removal, and heat-relaxing
Implementation Method 2
The microporous membrane has numerous microscopic pores that are connected to one another, providing permeability
Data Source
Figure 1
Figure 2~3(c)
Figure 4~5
AI summary
A polyethylene microporous membrane having a Gurley air permeability of 1 to 1,000 sec/100 mL/25 µm, wherein the total length of waviness widths in the width direction of the polyethylene microporous membrane is not more than one-third of the overall width of the microporous membrane, and a process for producing the same. Provided is a polyethylene microporous membrane having excellent planarity without compromising any other important physical property such as permeability.