Polyimide Nanoweb Separator for Thermal Stability
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Solution Overview
Problem
Lithium-ion batteries face challenges with mechanical integrity, solvent absorption, and thermal stability due to the limitations of current separator materials, which can lead to short circuits and explosions, and require additional safety measures like fuses and temperature sensors.
Innovation Solution
A multi-layer article with a porous separator comprising a nanoweb of fully aromatic polyimide nanofibers, which is fabricated by electroblowing or electrospinning and imidized at a selected temperature, followed by further heat treatment to enhance strength and reduce solvent uptake, providing improved mechanical and electrochemical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microporous polypropylene is used as separator, then manufacturing is simple and cost-effective, but thermal stability is limited (shrinkage at 120°C)
Solution Approach 1:
The patent changes the material parameter from polypropylene to polyimide, which fundamentally alters the thermal properties. Polyimide nanofibers maintain dimensional stability at temperatures above 120°C, eliminating the shrinkage problem while preserving the microporous structure needed for ion transport.
Solution Approach 2:
The patent creates a composite structure using nanoscale polyimide fibers with controlled porosity. The nanofiber morphology provides both thermal stability and the necessary pore structure for battery operation, combining properties that were previously mutually exclusive.
2Quantity of substance
If non-woven separators are used, then porosity is high for ion transport, but mechanical strength is inadequate
Solution Approach 1:
The patent transitions from conventional micrometer-scale fibers to nanoscale fibers (1-100 nm diameter). This dimensional change increases the surface area-to-volume ratio, allowing the nanofibers to form a mechanically robust network while maintaining high porosity for ion transport.
Solution Approach 2:
The patent employs a controlled porous structure formed by the nanofiber network. The porosity is optimized to allow lithium ion transport while the nanoscale fiber architecture provides mechanical reinforcement, solving the strength-porosity trade-off.
3Strength
If polyethylene microporous films are used, then mechanical strength is sufficient, but thermal suitability is poor at high temperatures
Solution Approach 1:
The patent changes the chemical composition from polyethylene to polyimide, which fundamentally alters the thermal behavior. Polyimide's aromatic structure provides exceptional thermal stability, allowing the separator to maintain both strength and dimensional integrity at high temperatures where polyethylene would deform.
4Productivity
If separator undergoes mechanical stress during winding and use, then tight winding is achieved, but manufacturing defects and device failure occur
Solution Approach 1:
The patent uses a flexible thin film structure made of nanofibers that can withstand mechanical stress during winding. The nanofiber network's flexibility and韧性 allow the separator to be tightly wound without creating defects, while maintaining structural integrity during battery operation.
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 nanoweb separator exhibits high strength, low solvent absorption, and enhanced thermal stability, reducing the risk of short circuits and explosions, and maintaining performance in lithium-ion batteries, thereby improving safety and durability.
Implementation Method 1
a method of fabricating a nanoweb by assembling nanofibers to form a nanoweb wherein the nanofibers comprise a polyamic acid; imidizing the polyamic acid nanofibers at a selected temperature to provide a nanoweb comprising polyimide nanofibers
Implementation Method 2
the manufactured device can be subject to shaking and impact stresses during use
Implementation Method 3
subjecting the nanoweb to a temperature at least 50° C. higher than the selected temperature for a period of time in the range of about 5 seconds to about 20 minutes
Data Source
AI summary
This invention provides a multi-layer article comprising a first electrode material, a second electrode material, and a porous separator disposed between and in contact with the first and the second electrode materials, wherein the porous separator comprises a nanoweb consisting essentially of a plurality of nanofibers of a fully aromatic polyimide. Also provided is a method for preparing the multi-layer article, and an electrochemical cell employing the same. A multi-layer article comprising a polyimide nanoweb with enhanced properties is also provided.