Microporous Battery Separator Composition for Defect-Resistant Extrusion
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Solution Overview
Problem
Microporous membranes used in power storage devices, such as lithium-ion batteries, face issues with defects during material mixing and extrusion steps, leading to reduced cycle characteristics and increased aggregation or gelling, which affects the performance and longevity of the batteries.
Innovation Solution
A method for producing a separator with a microporous membrane composed of polyethylene and polypropylene, where the crystallite sizes of PE are between 15 nm to 40 nm and PP are between 10 nm to 50 nm, optimized by controlling the molecular weight and crystallinity, and using a specific weight ratio to enhance ion permeability and mechanical strength, thereby reducing defects and improving cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polyolefin microporous membranes are used as separators, then manufacturing process is simple, but defects occur during mixing and extrusion leading to reduced cycle characteristics
Solution Approach 1:
The patent changes the molecular weight parameter of the polyolefin resin to 500,000 or greater (ultrahigh molecular weight), which fundamentally alters the material properties. This parameter change enables the resin to maintain high strength and reduced defects during extrusion while improving cycle characteristics through better adhesion to electrodes and resistance to compression during battery operation.
Solution Approach 2:
The patent creates a composite structure by combining ultrahigh molecular weight polyolefin resin with specific additives including inorganic particles (such as alumina, silica) and organic compounds. This composite approach improves manufacturing precision by reducing defects while enhancing reliability through better mechanical properties and cycle characteristics.
2Stability of the object's composition
If separator films undergo repetitive compressive force and release, then volume recovery is needed, but pore diameter structure is destroyed or irreversibly compressed
Solution Approach 1:
The patent changes the molecular weight parameter to ultrahigh levels (500,000+), which provides the polymer chains with sufficient entanglement and strength to withstand repetitive compression. This enables the separator to recover its original pore structure after compression cycles, maintaining both volume recovery and pore diameter integrity throughout battery operation.
Solution Approach 2:
The patent incorporates inorganic particles and specific additives beforehand to reinforce the microporous structure. These additives act as structural support elements that prevent irreversible compression of the pore diameter while maintaining volume recovery capability during charge-discharge cycles.
3Strength
If high strength and high specific surface area are achieved, then manufacturing complexity increases
Solution Approach 1:
The patent achieves high strength by changing the fundamental molecular weight parameter to ultrahigh levels (500,000+). This single parameter change provides inherent strength without requiring complex manufacturing processes, as the ultrahigh molecular weight resin naturally forms a stronger, more defect-resistant structure during standard extrusion.
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 method results in a separator with reduced defects and improved cycle characteristics, allowing for better volume recovery and adhesion to negative electrodes, which enhances the performance and longevity of power storage devices by preventing void formation and excessive solid electrolyte interface growth.
Implementation Method 1
extracting the liquid plasticizer from the stretched sheet to form a microporous membrane
Data Source
AI summary
Provided is a method for producing a separator for a power storage device, the method including: a step for extruding powdered polyethylene, pelletized polypropylene, and a plasticizer into a sheet form using an extruder to form a molded body; and a step for making the molded body porous by a wet method.