Interpenetrating Polymer Battery Separator for High-Temperature Stability
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Solution Overview
Problem
Existing lithium-ion battery separators exhibit poor dimensional stability at high temperatures, leading to deformation and potential short circuits, and have inadequate ion permeability and adhesion with electrode materials, which affects battery efficiency and safety.
Innovation Solution
A multilayer microporous separator with an interpenetrating network structure is developed, comprising a PVDF layer and a PE-PVDF porous substrate, where the PE-PVDF substrate is prepared by melt extrusion and laminated with a PVDF sheet, enhancing thermal stability and adhesion through biaxial orientation and thermoforming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pure polyethylene separator with single aperture structure is used, then the manufacturing process is simple, but the ion permeability is insufficient and safety cannot be achieved by preventing electrode material passage
Solution Approach 1:
The separator is divided into three functional layers: a PVDF substrate layer providing mechanical strength and thermal stability, a PE microporous layer with 20-50 nm pores for ion permeability and safety shutdown function, and an interpenetrating network layer with 50-100 nm pores for enhanced adhesion. This segmentation allows each layer to specialize in one function, resolving the contradiction between safety performance and structural complexity.
Solution Approach 2:
The invention employs porous structures at multiple scales: the PVDF substrate provides finger-like macropores, the PE layer provides micropores (20-50 nm), and the interpenetrating network provides mesopores (50-100 nm). This multi-scale porosity system simultaneously achieves high ion permeability through the smaller pores while maintaining mechanical integrity through the larger pores, resolving the contradiction between ion permeability and structural strength.
2Temperature
If polyethylene and polypropylene are used as separator materials, then the processing is easy, but the dimensional stability at high temperature is poor causing separator deformation
Solution Approach 1:
The invention changes the material composition parameters by incorporating PVDF (polyvinylidene fluoride) as the substrate material instead of traditional polyethylene or polypropylene. PVDF has a higher melting point and better dimensional stability at elevated temperatures. The processing difficulty is managed by optimizing the extrusion temperature (150-160°C) and using a twin-screw extruder for thorough mixing, thus resolving the contradiction between thermal stability and ease of manufacture.
Solution Approach 2:
The separator uses a composite structure combining PVDF as the base material with PE (polyethylene) layers. This composite material system leverages the high-temperature stability of PVDF while incorporating the beneficial shutdown function of PE. The composite approach resolves the contradiction by combining materials with complementary properties, achieving both thermal stability and manufacturability.
3Strength
If a single-layer separator structure is used, then the manufacturing cost is low, but the adhesion between electrode material and separator is low causing electrode separation
Solution Approach 1:
The invention applies local quality by creating an interpenetrating network layer at the interface between the PVDF substrate and PE layer. This specific region has a pore size of 50-100 nm, which is larger than the PE layer pores but smaller than the PVDF macropores. This localized structural modification at the interface provides enhanced adhesion strength without requiring complete restructuring of the entire separator, thus resolving the contradiction between adhesion strength and structural complexity.
Solution Approach 2:
The invention adds a new dimensional aspect to the separator structure by creating an interpenetrating network that spans across the interface between layers. This interpenetrating structure creates a three-dimensional interconnected pore system that mechanically interlocks the PVDF substrate and PE layer, significantly enhancing interfacial adhesion. This dimensional approach resolves the contradiction by adding structural complexity only where needed at the interface rather than throughout the entire separator.
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 interpenetrating network structure improves thermal stability, ion transport efficiency, and safety by preventing electrode material passage, while PVDF acts as an adhesive, enhancing battery stability and preventing internal short circuits.
Implementation Method 1
the PE-PVDF porous substrate is suitable for being prepared by melt extrusion of a PE-PVDF mixture
Implementation Method 2
the PVDF layer is derived from a PVDF precursor and prepared by thermally induced phase transformation
Implementation Method 3
An interpenetrating network structure with a pore size of 50-100 nm is distributed on an interface between the PVDF finger-like pore layer and the PE microporous layer
Implementation Method 4
PVDF acts as an adhesive, enhancing the adhesion between an electrode and the multilayer microporous separator
Implementation Method 5
carrying out a biaxial orientation
Implementation Method 6
performing a thermoforming to obtain the multilayer microporous separator
Data Source
AI summary
A polymer battery separator with an interpenetrating network structure and a preparation method thereof are disclosed. A multilayer microporous separator includes a PVDF layer, and a PE-PVDF porous substrate located on a surface of the PVDF layer. Finger-like through holes with a pore size of 100-150 nm are distributed in the PVDF finger-like pore layer. An interpenetrating network structure with a pore size of 50-100 nm is distributed on an interface between the PVDF finger-like pore layer and the PE microporous layer. Micropores with a pore size of 20-50 nm are distributed in the PE microporous layer. The surface of the PVDF layer is covered with the PE-PVDF porous substrate, so that the multilayer microporous separator forms an interpenetrating network structure, which has improved thermal stability and high-temperature resistance.