Porous Multi-Layer Battery Separator with Dual Pore Structure
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Solution Overview
Problem
Current lithium ion secondary battery separators lack simultaneous improvement in thermal stability, electrolyte retaining properties, and battery assembling stability, with existing methods either compromising on permeability, strength, or causing defects like pin-holes and non-uniformity.
Innovation Solution
A porous multi-layer film with a dual pore structure, comprising a first layer with 30-60% porosity and 0.01-0.1µm pore diameter, and a second layer with 50-80% porosity and 70% or more area ratio of 0.1-50µm pores, achieving a thickness ratio of 30-70%, loop stiffness of 0.008mg/µm or more, and puncture strength of 0.15N/µm or more, while maintaining shut-down and melt fracture temperatures within specific ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If inorganic materials are added to polyethylene separator, then thermal stability is improved, but mixing performance deteriorates and pin-holes are generated
Solution Approach 1:
The separator is divided into multiple layers with distinct functions: a polyethylene base layer for shutdown function, and a heat-resistant polymer layer containing inorganic materials for thermal stability. This segmentation allows each layer to be optimized independently, preventing mixing performance deterioration while maintaining thermal stability improvement.
Solution Approach 2:
The invention uses a composite structure combining polyethylene with heat-resistant polymers (such as polypropylene, polyvinylidene fluoride, or carboxymethyl cellulose) and inorganic materials (such as alumina, silica, or boehmite). This composite approach allows the heat-resistant components to be distributed uniformly without causing pin-holes, as the composite structure accommodates the inorganic materials within the polymer matrix.
2Temperature
If polypropylene is added to polyethylene separator, then thermal stability is improved, but physical property deteriorates due to poor mixing
Solution Approach 1:
The heat-resistant polymer and inorganic materials are concentrated in a specific layer rather than being uniformly distributed throughout the entire separator. This local quality approach ensures that the polyethylene base layer maintains its excellent physical properties and shutdown function, while the heat-resistant layer provides thermal stability where needed.
Solution Approach 2:
The use of composite materials with specific heat-resistant polymers combined with inorganic fillers creates a synergistic effect. The polymer matrix provides structural integrity and good mixing performance, while the inorganic materials provide thermal resistance. This composite structure prevents the physical property deterioration that occurs when polypropylene is simply mixed with polyethylene.
3Temperature
If coating method is used to improve thermal stability, then thermal resistance is increased, but permeability decreases and quality uniformity deteriorates
Solution Approach 1:
Instead of coating the heat-resistant layer on the surface, the invention segments the separator into multiple layers where the heat-resistant polymer and inorganic materials form an integrated layer within the separator structure. This segmentation ensures uniform distribution of thermal resistance properties throughout the separator without creating surface defects or permeability issues associated with coating methods.
Solution Approach 2:
The composite material structure with heat-resistant polymers and inorganic materials creates a uniformly distributed thermal resistance network throughout the separator. This composite approach avoids the wetting property deterioration and non-uniform quality that occur with coating methods, as the materials are integrated into the separator matrix rather than applied as a surface coating.
4Temperature
If multi-layer lamination is used to improve thermal stability, then thermal properties are improved, but productivity deteriorates due to additional process steps
Solution Approach 1:
The invention merges the base polyethylene layer and the heat-resistant layer into a single integrated separator structure formed in one continuous process. By combining the formation of the polyethylene matrix and the heat-resistant polymer-inorganic material layer into a single manufacturing step, the invention eliminates the separate lamination process steps, thereby improving productivity while maintaining the multi-layer thermal stability benefits.
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 film exhibits superior thermal stability, electrolyte retaining properties, and battery assembling stability, ensuring high-capacity and high-power lithium ion battery performance with improved quality uniformity and permeability.
Implementation Method 1
a porous multi-layer film including a first layer having porosity of 30 to 60% and an average pore diameter of 0.01 to 0.1µm, and a second layer having porosity of 50 to 80%
Implementation Method 2
a first layer having porosity of 30 to 60% and an average pore diameter of 0.01 to 0.1µm
Implementation Method 3
mixing 30 to 75 wt% organic liquid and 10 to 50 wt% inorganic materials with a resin mixture where polyethylene is mixed with 5 to 45 wt% polypropylene
Data Source
Figure 1~2
AI summary
Provided is a porous multi-layer film having two or more layers that is used as a separator for battery. In the film, more than 2 layers have different porosities and pore sizes. The film has a thickness of 9 to 50㎛, a machine direction (MD) loop stiffness of 0.008mg/㎛ or more, puncture strength of 0.15N/㎛ or more, permeability of 1.5 x 10-5Darcy or more, shut-down temperature of 140℃ or less, melt-down temperature of 170℃ or more, a transverse direction (TD) maximum shrinkage of 25% or less in Thermomechanical Analysis (TMA) under a load of 1mN/(1㎛ x 6mm), and melt down temperature of 160℃ or more. Since the porous multi-layer film shows excellent thermal stability at high temperature and electrolyte retaining property due to a dual pore structure, the film shows a superior effect when used as a separator for high-capacity/high-power lithium ion battery.