Polylactam-Ceramic Separator Membranes With Reduced Heat Shrinkage
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Solution Overview
Problem
Current lithium ion battery separators face challenges with thermal stability, chemical stability, and dimensional integrity, particularly at high temperatures, which can lead to safety issues such as short circuits due to thermal shrinkage.
Innovation Solution
A polylactam ceramic coating is applied to a microporous polyolefin separator membrane using an aqueous medium, combining a polylactam polymeric binder with inorganic particles, which provides excellent thermal and chemical stability, improved adhesion, and reduced thermal shrinkage, enhancing the safety and performance of lithium ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an aromatic-polyamide (aramid) porous membrane is used to provide heat resistance, then thermal stability is improved, but the coating requires non-aqueous solvents like NMP and involves complex phase separation processes
Solution Approach 1:
The patent changes the solvent parameter from non-aqueous (NMP) to aqueous medium, and changes the polymer chemistry from aramid to polylactam-ceramic composite. This allows the coating to be applied through simpler dip-coating or spray-coating methods without requiring complex phase separation processes, while maintaining heat resistance through the ceramic component.
Solution Approach 2:
The patent uses a composite material system combining polylactam polymer with ceramic particles. The polylactam provides adhesion and film formation in aqueous medium, while the ceramic particles provide thermal stability and heat resistance. This composite approach allows simplified processing while achieving the desired thermal performance.
2Strength
If (meth)acrylic polymeric binder with ceramic particles is used, then adhesion between ceramic particles and binder is improved, but the binder is prone to chain scission in electrolytes reducing chemical stability
Solution Approach 1:
The patent changes the polymer chemistry from (meth)acrylic to polylactam. Polylactam polymers contain amide bonds that form strong hydrogen bonding networks, providing excellent adhesion to ceramic particles without the chain scission problem. The polylactam structure is chemically stable in lithium ion battery electrolytes, maintaining both adhesion and chemical stability simultaneously.
3Ease of manufacture
If polyethylene wax powder and surface treated ceramic particles are added to prepare stable emulsified coating slurry, then ease of manufacture is improved, but thermal shrinkage reduction is insufficient at high temperatures
Solution Approach 1:
The patent uses a composite of polylactam polymer with inorganic ceramic particles (such as alumina, silica, or boehmite). The ceramic particles provide high temperature stability and resist thermal shrinkage at temperatures above 150°C, while the polylactam matrix ensures slurry stability and adhesion. This composite system achieves both manufacturing ease and high temperature performance.
4Reliability
If coating is applied to improve dimensional integrity and reduce thermal shrinkage, then safety is improved, but the coating process becomes more complex
Solution Approach 1:
The patent changes the solvent system to aqueous medium and uses polylactam polymer that forms stable coatings through simple dip-coating or spray-coating processes. The coating can be applied in one or two layers without requiring complex multi-step processes, achieving good dimensional integrity and thermal shrinkage resistance while keeping the device complexity low.
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 polylactam ceramic coating significantly reduces thermal shrinkage and maintains dimensional integrity at high temperatures, improving the safety and performance of lithium ion batteries, especially in high-energy applications like electric vehicles.
Implementation Method 1
excellent adhesion to microporous base substrate, membrane, and/or electrode, improved binding properties to ceramic particles
Implementation Method 2
improved, optimized, novel, or excellent resistance to thermal shrinkage, dimensional integrity
Data Source
AI summary
The present invention is preferably directed to a polylactam ceramic coating for a microporous battery separator for a lithium ion secondary battery and a method of making this formulation and application of this formulation to make a coated microporous battery separator. The preferred inventive coating has excellent thermal and chemical stability, excellent adhesion to microporous base substrate, membrane, and/or electrode, improved binding properties to ceramic particles and/or has improved or excellent resistance to thermal shrinkage, dimensional integrity, and/or oxidation stability when used in a rechargeable lithium ion battery.