Composite Separator Binder Design for Low Thermal Shrinkage
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Solution Overview
Problem
The existing composite separators for lithium-ion batteries face challenges in maintaining thermal stability and preventing thermal runaway due to high thermal shrinkage rates at elevated temperatures, which can lead to electrode contact and safety concerns.
Innovation Solution
A composite separator is developed with a porous polyolefin substrate coated with an inorganic coating layer containing a specific binder resin composition. The binder resin composition includes an acrylonitrile-acrylamide-acrylate copolymer with a glass transition temperature less than 0 °C and an amide-containing polymer with a glass transition temperature between 150 °C and 200 °C, along with inorganic particles. This configuration enhances the adhesion and high-temperature resistance of the interface while maintaining flexibility and rigidity to resist thermal shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the ceramic coating layer is increased to enhance shrinkage resistance, then the thermal shrinkage resistance is improved, but the overall thickness of the separator increases which affects battery energy density
Solution Approach 1:
The patent changes the chemical composition parameters of the binder resin to achieve optimal performance. Specifically, it uses a binder resin containing carboxylic acid groups with a content of 0.5 to 5.0 mmol/g, which creates strong chemical bonding between the ceramic particles and substrate. This parameter optimization allows the ceramic layer to maintain high shrinkage resistance at reduced thickness, resolving the contradiction between thermal stability and separator thickness.
2Ease of manufacture
If conventional binder resins are used to make ceramic particles adhere onto the polyolefin substrate, then the ceramic coating can be formed, but the strength of the binder resin decreases at high temperatures causing structural damage and thermal decomposition
Solution Approach 1:
The patent changes the chemical structure parameters of the binder resin by selecting polymers with specific glass transition temperatures (Tg). It uses a first polymer with 80 ≤ Tg ≤ 120°C and a second polymer with 140 ≤ Tg ≤ 200°C, ensuring the binder maintains structural integrity at high temperatures while still enabling effective ceramic particle adhesion during manufacturing.
Solution Approach 2:
The patent employs a composite binder resin system combining two different polymers with complementary properties. The first polymer (lower Tg) provides flexibility and adhesion, while the second polymer (higher Tg) provides high-temperature stability. This composite approach allows the binder to simultaneously achieve ease of manufacture and high-temperature reliability.
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 composite separator achieves a thermal shrinkage ratio of not more than 2% at 150°C, effectively preventing electrode contact and thermal runaway. The enhanced adhesion between the substrate and the inorganic coating layer ensures high peeling strength, further improving safety and performance.
Implementation Method 1
The binder resin composition comprises an acrylonitrile-acrylamide-acrylate copolymer with a glass transition temperature (Tg) less than 0 °C and an amide-containing polymer with a glass transition temperature between 150 °C and 200 °C
Implementation Method 2
an acrylonitrile-acrylamide-acrylate copolymer with a glass transition temperature (Tg) less than 0 °C
Implementation Method 3
an amide-containing polymer with a glass transition temperature between 150 °C and 200 °C
Implementation Method 4
the strength of the resin binders is prone to decrease at high temperatures, and may even cause structural damage and thermal decomposition, which will significantly reduce the shrinkage resistance of the composite separator
Data Source
AI summary
A composite separator and a method for manufacturing thereof are disclosed. The composite separator comprises a porous polyolefin substrate and an inorganic coating layer, wherein the inorganic coating layer comprises a plurality of inorganic particles and a binder resin composition and coated on at least one surface of the porous polyolefin substrate, wherein the binder resin composition comprises an acrylonitrile-acrylamide-acrylate copolymer with a glass transition temperature (Tg) less than 0 °C and an amide-containing polymer with a glass transition temperature between 150 °C and 200 °C. The composite separator has good high temperature resistance.