Microporous Polyolefin Membrane Separator Thickness Control
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Solution Overview
Problem
Lithium ion battery separators face challenges with heat resistance, electrode adhesion, and permeability, particularly when the porous layer thickness varies significantly along the length of the membrane, leading to increased production costs and reduced battery capacity due to thickness variations and winding issues.
Innovation Solution
A polyolefin microporous membrane with a controlled F25 value variation range of 1 MPa or less, combined with a porous layer composed of fluorine resins, acrylic resins, or polyvinyl alcohol resins, applied using a roll coating method to achieve uniform thickness and improved battery separator performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous layer is provided on a polyolefin microporous membrane to improve heat resistance and adhesion, then battery safety and electrode adhesion are enhanced, but production costs increase and thickness variations cause winding defects
Solution Approach 1:
The patent controls the F25 value (tensile strength at 25% elongation) of the polyolefin microporous membrane within a specific range (0.01 to 0.05 N/μm) to achieve optimal balance between heat resistance, adhesion, and manufacturability. This parameter optimization allows the porous layer to be applied effectively without excessive thickness variation, thereby maintaining battery safety while controlling production costs.
2Reliability
If the porous layer thickness is increased to improve adhesion and heat resistance, then battery safety is enhanced, but thickness variations lead to winding defects and reduced battery capacity
Solution Approach 1:
The patent specifies that the porous layer thickness should be controlled within 3 to 20 μm with a thickness variation of less than 5 μm along the membrane length. This precise thickness control ensures uniform adhesion and heat resistance while preventing winding defects that would occur with excessive thickness variation.
Solution Approach 2:
The patent applies the porous layer to the polyolefin microporous membrane before battery assembly, ensuring uniform adhesion properties are established in advance. This preliminary action prevents adhesion issues during battery operation and avoids winding defects that would compromise battery capacity.
3Productivity
If the polyolefin microporous membrane is stretched to create micropores for ion permeability, then ion transport is enabled, but membrane rupture may occur at high temperatures due to shrinkage
Solution Approach 1:
The patent creates a composite structure by applying a porous layer (containing inorganic particles and binder) onto the polyolefin microporous membrane. The inorganic particles in the porous layer maintain structural stability at high temperatures, preventing membrane rupture while the micropores in the underlying polyolefin membrane continue to provide ion permeability for battery operation.
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 solution ensures a uniform porous layer thickness, enhancing the battery separator's heat resistance, adhesion, and permeability, while reducing production costs and improving battery capacity by maintaining consistent thickness and reducing winding defects.
Implementation Method 1
applied using a roll coating method to achieve uniform thickness
Implementation Method 2
The thus obtained coating solution is then dried
Data Source
AI summary
A polyolefin microporous membrane has a variation range of F25 value in a longitudinal direction of 1 MPa or less; a thickness of 3 μm or more and less than 7 μm; and a length of 1,000 m or more (wherein the F25 value is a value obtained by measuring a load value applied to a test specimen when the test specimen is stretched by 25% using a tensile tester; and dividing the load value by a value of a cross-sectional area of a test specimen).