Laminated Polyolefin Separator for Li-Ion Battery Capacity
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Solution Overview
Problem
Current polyolefin microporous membranes for lithium ion batteries face challenges in achieving high permeability, mechanical strength, and high-temperature storage characteristics while being thin enough to increase battery capacity per unit volume, with issues of low impregnation with electrolyte, mechanical strength, and uniformity.
Innovation Solution
A laminated polyolefin microporous membrane with a three-layer structure, where the surface layers contain inorganic particles and polypropylene, and the interlayer contains polyethylene, optimized for thickness, gas transmission rate, and mechanical strength, produced through melt kneading, extrusion, and biaxial stretching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the separator is thinned to increase battery capacity per unit volume, then the battery capacity per unit volume increases, but the mechanical strength and impregnation with electrolyte deteriorate
Solution Approach 1:
The patent applies composite materials by combining polyethylene microporous membrane with inorganic particles (such as alumina, silica, or titania) to create a laminated structure. This composite approach allows the separator to maintain mechanical strength and electrolyte impregnation properties even at reduced thickness, thereby increasing battery capacity per unit volume without sacrificing structural integrity.
Solution Approach 2:
The invention applies local quality by creating a laminated structure where the polyethylene layer provides shutdown function and the inorganic particle-containing layer provides mechanical strength and thermal stability. This localized functional differentiation allows each layer to optimize its specific property, enabling thin overall thickness while maintaining necessary mechanical strength and electrolyte impregnation.
2Quantity of substance
If the separator is thinned to increase battery capacity per unit volume, then the battery capacity per unit volume increases, but the impregnation with electrolyte deteriorates
Solution Approach 1:
The composite structure combines polyethylene microporous membrane with inorganic particles creates a laminated separator that maintains excellent electrolyte impregnation properties even at thin thickness. The inorganic particles provide a porous network that facilitates electrolyte penetration and retention, ensuring reliable ionic conduction pathways despite reduced overall separator thickness.
Solution Approach 2:
The invention utilizes porous materials by incorporating inorganic particles with controlled pore structures into the separator. These porous inorganic layers provide extensive surface area and interconnected void spaces that enhance electrolyte impregnation and retention, allowing the thin separator to maintain high ionic conductivity and reliable electrolyte contact.
3Temperature
If filler is contained in the separator to develop high heat resisting temperature, then the heat resistance improves, but the separator cannot be thinned and uniformity deteriorates
Solution Approach 1:
The patent applies composite materials by creating a laminated structure where polyethylene and inorganic particles are combined in specific layers. This composite approach achieves high heat resistance through the inorganic components while the layered architecture prevents agglomeration, ensuring uniform distribution and manufacturing precision. The lamination process allows controlled placement of fillers, maintaining membrane uniformity.
Solution Approach 2:
The invention applies segmentation by dividing the separator into multiple functional layers: a polyethylene layer for shutdown function and an inorganic particle-containing layer for heat resistance. This segmentation prevents filler agglomeration by confining inorganic particles to specific layers, ensuring uniform distribution throughout the separator structure and maintaining manufacturing precision while achieving high heat resistance.
4Quantity of substance
If electrodes are densely packed to increase capacity, then the battery capacity increases, but the impregnation with electrolyte and mechanical strength of separator deteriorate
Solution Approach 1:
The composite laminated structure with inorganic particles provides enhanced mechanical strength and porous network that maintains excellent electrolyte impregnation even under the strong mechanical load of densely packed electrodes. The inorganic layer acts as a rigid support framework that prevents separator collapse and maintains open pore structures for electrolyte penetration, enabling high battery capacity through dense electrode packing without compromising separator performance.
5Quantity of substance
If electrodes are densely packed to increase capacity, then the battery capacity increases, but the mechanical strength of separator deteriorates
Solution Approach 1:
The invention applies composite materials by combining polyethylene with inorganic particles (alumina, silica, or titania) in a laminated structure. The inorganic particles provide rigid mechanical support and high tensile strength to the separator, enabling it to withstand the strong mechanical loads from densely packed electrodes without tearing or deforming, thus maintaining structural integrity while allowing high battery capacity through dense packing.
Solution Approach 2:
The laminated structure applies local quality by concentrating the mechanical strength enhancement in the inorganic particle-containing layer, while the polyethylene layer maintains its shutdown function. This localized reinforcement allows the separator to handle high mechanical loads from dense electrode packing without compromising the overall flexibility and shutdown characteristics of the thin separator structure.
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 membrane exhibits improved permeability, mechanical strength, high impregnation with electrolyte, and enhanced high-temperature storage characteristics, maintaining insulation and safety even at elevated temperatures, thus addressing the limitations of existing separators.
Implementation Method 1
Polyethylene microporous membranes are used as separators for lithium ion batteries because they are high in permeability
Implementation Method 2
they have a function to clog the communicating pores upon melting the polymer at 130-150° C. and to shut-down the current
Implementation Method 3
produced through melt kneading, extrusion, and biaxial stretching
Data Source
AI summary
Disclosed is a polyolefin microporous membrane including a multilayer film having two or more layers. In this polyolefin microporous membrane, at least one surface layer has a thickness of not less than 0.2 μm but not more than 5 μm and contains inorganic particles, while at least one layer contains a polyethylene and has an air permeability of not less than 50 second/100 cc but not more than 1000 second/100 cc and a puncture strength of not less than 3.0 N/20 μm.