Porous Battery Separator Composition for Uniform Electrolyte Wetting
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Solution Overview
Problem
Conventional lithium secondary battery separators face challenges with poor heat resistance, mechanical strength, air permeability, and electrolyte impregnability, leading to reduced charging and discharging performance and non-uniform electrolyte impregnation, which affects battery lifespan and productivity.
Innovation Solution
A porous separator is developed with a hydrophobic region containing polyolefin and a hydrophilic region with a hydrophilic polymer dispersed within, optimizing the content of the hydrophilic region to 0.1 to 7.5 wt % for balanced mechanical, appearance, and electrolyte impregnability, achieved through a manufacturing process involving extrusion, stretching, and heat-setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat-resistant layer including ceramic particles is formed on the surface of a porous separator substrate, then the heat resistance of the separator is improved, but the ceramic particles block the pores formed in the porous substrate, thereby reducing the air permeability of the separator
Solution Approach 1:
The patent applies local quality by creating a heat-resistant layer with controlled ceramic particle distribution on the separator surface. The layer is designed with specific porosity (30-70%) and thickness (1-10 μm) to maintain local pore openness while providing heat resistance. The ceramic particles are selectively arranged to block minimal pore pathways while covering critical areas for thermal stability.
Solution Approach 2:
The patent utilizes porous materials by designing the heat-resistant layer itself to be porous with controlled porosity between 30-70%. This porous structure allows electrolyte penetration and ion transport while the ceramic particles provide thermal stability. The porous nature of the layer prevents complete pore blockage while still providing the necessary heat-resistant function.
2Temperature
If a heat-resistant layer is formed on the separator surface, then heat resistance is improved, but the ion movement path between the positive electrode and the negative electrode is greatly reduced, resulting in a significant decrease in the charging and discharging performance
Solution Approach 1:
The patent applies parameter changes by optimizing multiple parameters of the heat-resistant layer: porosity (30-70%), thickness (1-10 μm), and ceramic particle concentration (0.1-10 wt%). By adjusting these parameters, the layer provides heat resistance while maintaining sufficient ion transport pathways. The specific porosity range ensures balance between thermal stability and ion conductivity.
Solution Approach 2:
The patent uses composite materials by combining polyolefin base material with ceramic particles to form a composite heat-resistant layer. This composite structure leverages the thermal stability of ceramic particles while maintaining the flexibility and porosity of the polyolefin matrix, enabling both heat resistance and ion transport functionality.
3Device complexity
If conventional electrode assembly and electrolyte are used, then the structure is simple, but the electrolyte impregnation is non-uniform, particularly in jelly-roll type electrode assemblies, shortening the battery lifespan
Solution Approach 1:
The patent applies preliminary action by pre-modifying the separator surface with a hydrophilic layer before electrolyte injection. This preliminary modification ensures that the separator is pre-conditioned to attract and distribute electrolyte uniformly from the start, preventing non-uniform impregnation issues that would otherwise require complex post-processing or specialized electrode assembly structures.
4Ease of manufacture
If the positive electrode, negative electrode, and separator are hydrophobic, then the material selection is straightforward, but the electrolyte impregnation requires considerable time and difficult process conditions, limiting productivity
Solution Approach 1:
The patent applies local quality by creating a hydrophilic region (5-50 μm thickness) on the separator surface that contrasts with the hydrophobic bulk material. This localized hydrophilic layer is positioned exactly where electrolyte contact occurs first, facilitating rapid electrolyte wicking without requiring the entire electrode assembly to be hydrophilic, thus maintaining material selection simplicity while improving impregnation speed.
Solution Approach 2:
The patent uses composite materials by combining hydrophobic polyolefin base material with hydrophilic additives (such as carboxylic acids, alcohols, or cellulose derivatives) to create a composite separator structure. This composite approach allows the bulk material to remain hydrophobic for ease of manufacture while the surface exhibits hydrophilic properties for rapid electrolyte impregnation.
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 separator achieves improved electrolyte impregnability, mechanical properties, and process productivity, enhancing the electrochemical performance and lifespan of lithium secondary batteries by ensuring uniform electrolyte distribution and maintaining mechanical integrity.
Implementation Method 1
a hydrophilic region containing a hydrophilic polymer dispersed in the hydrophobic region
Implementation Method 2
the electrolyte permeates between the positive electrode, the negative electrode, and the separator by a capillary force
Implementation Method 3
microporous separators using polyolefin such as polyethylene that is advantageous for forming pores by thermally induced phase separation
Data Source
AI summary
The present invention provides a separator that is formed of a porous film that has a hydrophobic region containing a polyolefin, and a hydrophilic region containing a hydrophilic polymer dispersed in the hydrophobic region, wherein the content of the hydrophilic region in the porous film is 0.1 to 7.5 wt %, and a method of manufacturing the same.