Polyimide Nonwoven Separator Adhesion for Thermal Stability
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Solution Overview
Problem
Current lithium-ion battery separators face challenges in combining high temperature stability, low shrinkage, and shutdown capabilities, with microporous polyolefin membranes providing good structural and barrier properties but limited safety performance, while nonwoven materials offer stability but poor shutdown capabilities.
Innovation Solution
A hybrid separator structure combining a polyimide nonwoven layer with a microporous polyolefin membrane, bonded using an adhesive-based process to ensure good adhesion without excessive permeability or resistance increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If microporous polyolefin membranes are used as separators, then good structural and barrier properties are achieved, but high temperature stability and shrinkage resistance are limited
Solution Approach 1:
The patent employs a composite separator structure consisting of a microporous polyolefin membrane layer bonded to a heat-resistant nonwoven layer. This composite design allows the polyolefin layer to provide excellent barrier properties and shutdown capabilities, while the heat-resistant nonwoven layer contributes high temperature stability and shrinkage resistance, thereby resolving the contradiction between barrier performance and thermal stability.
2Temperature
If nonwoven materials are used for high temperature stability, then low shrinkage and stability are achieved, but shutdown capabilities are poor
Solution Approach 1:
The composite separator structure combines a heat-resistant nonwoven layer with a microporous polyolefin membrane layer. The nonwoven layer provides the necessary high temperature stability and low shrinkage, while the polyolefin layer maintains excellent shutdown capabilities through its melting behavior at specific temperatures. This composite approach allows both requirements to be satisfied simultaneously.
3Strength
If adhesive bonding is used to combine layers, then good adhesion is achieved, but permeability reduction and resistance increase occur
Solution Approach 1:
The adhesive bonding is applied selectively and locally between the microporous polyolefin membrane layer and the heat-resistant nonwoven layer, rather than uniformly across the entire separator structure. This localized bonding approach ensures sufficient adhesion strength to maintain structural integrity while minimizing the total amount of adhesive material present, thereby reducing the impact on permeability and resistance characteristics.
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 hybrid separator structure achieves enhanced barrier properties, shutdown capabilities, and high temperature stability, improving the safety and performance of lithium-ion batteries while maintaining acceptable permeability and resistance levels.
Implementation Method 1
an adhesive binder layer located between the porous film and the fibrous layer, said binder layer comprising an adhesive
Data Source
AI summary
A heat-resistant separator contains a porous film, a polymeric fibrous layer adhesively bonded to the surface of the porous film, and an adhesive binder layer located between the porous film and the fibrous layer and covering at least a portion of the surface of the porous film. The fibrous layer contains fibers manufactured of a polyimide wherein the fibers of a form of polyimide comprise fibers with a majority of fibers having diameters in the range of 1-3000 nm. In one of the embodiment the binder layer contains sodium carboxymethylcellulose, and the amount of adhesive present between the porous film and the fibrous web in the final product is within the range of 0.30 grams per square meter of covered surface of porous film to 0.90 grams per square meter of covered surface of porous film.