Microporous Polyolefin Film via Liquid-Liquid Phase Separation
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Solution Overview
Problem
Current methods for preparing microporous polyolefin films, particularly for secondary battery applications, face limitations in controlling pore size and achieving high output and long life characteristics due to the constraints of solid-liquid phase separation methods, which restrict their suitability for advanced battery technologies.
Innovation Solution
A method involving the use of a novel diluent with higher Total Hansen solubility parameters than polyolefin, allowing for liquid-liquid phase separation, where the composition of polyolefin and diluent is processed under controlled temperature and retention time conditions to form a microporous film with adjustable pore size, achieved through extrusion and subsequent stretching, drying, and heat-setting processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solid-liquid phase separation method is used, then the film structure is formed by polymer crystallization, but the pore size and shape cannot be controlled variously
Solution Approach 1:
The patent changes the phase separation mechanism from solid-liquid to liquid-liquid phase separation, allowing control of pore size and shape through temperature parameters. By using a diluent with appropriate solubility parameters, the system achieves liquid-liquid phase separation above the polymer crystallization temperature, enabling versatile structural control that was not possible with crystallization-based methods.
Solution Approach 2:
The patent utilizes liquid-liquid phase separation instead of solid-liquid phase separation. The polymer and diluent form a single phase at high temperature, then separate into liquid phases upon cooling above the crystallization temperature, creating controllable porous structures. This phase transition approach enables precise control over pore characteristics.
2Manufacturing precision
If liquid-liquid phase separation method is used, then the pore size can be controlled, but a diluent with suitable liquid-liquid phase separation temperature must be found
Solution Approach 1:
The patent systematically evaluates diluents based on their solubility parameters (Hansen parameters) to identify those that exhibit liquid-liquid phase separation with polyolefin at processing temperatures. By establishing clear parameter criteria, the selection process becomes more systematic and manageable, reducing the complexity of finding suitable diluents.
Solution Approach 2:
The patent introduces the concept of using diluents with specific solubility parameter relationships as intermediaries to achieve controlled phase separation. The diluent acts as a mediator that enables liquid-liquid phase separation at desired temperatures, facilitating pore size control without requiring complex processing conditions.
3Reliability
If polyolefin is crystallized through cooling, then phase separation occurs as diluent is removed, but the separated phase size is very small and structure cannot be controlled
Solution Approach 1:
The patent replaces crystallization-based solid-liquid phase separation with temperature-induced liquid-liquid phase separation. By cooling the polymer-diluent mixture above the crystallization temperature, the system separates into liquid phases with different compositions, creating larger and more controllable pore structures compared to crystallization-based methods.
Solution Approach 2:
The patent changes the controlling parameter from crystallization temperature to liquid-liquid phase separation temperature. This parameter change allows the separated phase size and structure to be controlled through temperature and composition adjustments, rather than being constrained by crystal growth mechanisms.
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
This approach enables the production of microporous polyolefin films with controlled pore sizes, enhancing their suitability as high-performance battery separators by allowing for larger pore sizes and improved physical properties, thus meeting the demands of advanced secondary batteries.
Implementation Method 1
a step of extruding the melt while conducting liquid-liquid phase separation by passing through a section having a temperature below the liquid-liquid phase separation temperature
Implementation Method 2
a step of injecting a composition comprising polyolefin 30 to 60 wt % and a diluent 40 to 70 wt % into an extruding machine, and melting and kneading thereof to prepare a single phase melt
Implementation Method 3
extruding the melt while conducting liquid-liquid phase separation by passing through a section having a temperature below the liquid-liquid phase separation temperature
Data Source
AI summary
The present invention discloses a method for preparing a microporous polyolefin film comprising: a step of injecting a composition comprising polyolefin 30 to 60 wt % and a diluent, which can make liquid-liquid phase separation with the polyolefin thermodynamically 40 to 70 wt %, into an extruding machine, and melting and kneading thereof to prepare a single phase melt; and a step of extruding the melt while conducting liquid-liquid phase separation by passing through a section having the temperature below the liquid-liquid phase separation temperature and forming thereof in the form of a sheet, and a microporous polyolefin film prepared according to the method.