Separator Heat Resistant Insulation Layers Prevent Edge Curling
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Solution Overview
Problem
Conventional separators for flat laminated type non-aqueous electrolyte secondary batteries, such as those used in electric vehicles, are prone to edge curling during manufacturing, leading to defects and reduced yield rates due to thermal contraction mismatch between the resin porous substrate and heat-resistant insulation layers.
Innovation Solution
A separator with heat-resistant insulation layers formed on both surfaces of a resin porous substrate, where the thicknesses of these layers are optimized to ensure a parameter X greater than or equal to 0.15, balancing contraction stress and preventing curling, while maintaining ion permeability and rate property.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat resistant porous layers are stacked on surfaces of a microporous film to suppress thermal contraction, then thermal safety is improved, but edge curling occurs during battery manufacture
Solution Approach 1:
The invention changes the physical-chemical parameters of the heat resistant layer by controlling the glass transition temperature (Tg) of the binder to be 80°C or higher, and adjusting the weight ratio of heat resistant particles to binder within 95:5 to 5:95. These parameter changes modify the thermal behavior of the layer to match the substrate's contraction characteristics, preventing edge curling while maintaining thermal safety.
Solution Approach 2:
The invention addresses the thermal contraction mismatch by selecting heat resistant particles with specific thermal expansion characteristics and a binder with high glass transition temperature. This combination ensures that the heat resistant layer expands and contracts at rates compatible with the microporous film substrate during temperature changes, eliminating the stress that causes edge curling.
2Reliability
If heat resistant insulation layers are formed on both surfaces of the separator, then thermal contraction is suppressed, but manufacturing complexity increases
Solution Approach 1:
The invention uses porous heat resistant particles with specific surface areas (5 m²/g to 20 m²/g) and pore volumes (0.01 mL/g to 0.1 mL/g) that allow the formation of insulation layers with controlled porosity. This porous structure enables the layers to be formed with appropriate mechanical properties and thermal characteristics while maintaining a relatively simple single-layer configuration on each surface.
Solution Approach 2:
The invention creates a composite heat resistant layer combining inorganic or organic heat resistant particles with a specifically selected binder material. This composite structure provides both the thermal resistance function and the mechanical adhesion to the substrate, achieving thermal contraction suppression without requiring complex multi-layer or multi-component systems.
3Stability of the object's composition
If the thickness of heat resistant insulation layers is increased to prevent curling, then edge stability is improved, but ion permeability decreases
Solution Approach 1:
The invention utilizes the porous structure of the heat resistant particles and the controlled porosity of the insulation layer (40% to 70%) to maintain ion permeability even at increased thicknesses. The porous network allows ion transport through the layer while the overall thickness provides sufficient mechanical stability to prevent edge curling during manufacturing.
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 solution effectively prevents edge curling and enhances manufacturing reliability, improving yield rates and maintaining high output performance for large-size flat laminated type batteries.
Implementation Method 1
such a polyolefin microporous film has a risk of thermal contraction because of an increase in temperature inside the battery
Implementation Method 2
a polyolefin microporous film having a thickness approximately in the range from 20 μm to 30 μm is widely used as a separator
Data Source
Figure 1
Figure 2(a)~3
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AI summary
A separator (1) having heat resistant insulation layers for an electric device includes a resin porous substrate (2), and heat resistant insulation layers (3) formed on both surfaces of the resin porous substrate (2) and containing heat resistant particles having a melting point or a thermal softening point of 150°C or higher. A parameter X represented by the following mathematical formula 1 is greater than or equal to 0.15: X=Aʹ+AʹʹC×Aʹ/Aʹʹ2 where A' and A" represent thicknesses (µm) of the respective heat resistant insulation layers (3) formed on both surfaces of the resin porous substrate (2) while fulfilling a condition of A' ≥ A", and C represents the entire thickness (gm) of the separator (1) having heat resistant insulation layers.