Aromatic Polyimide Nanoweb Separator for Li-Ion Self-Discharge
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Solution Overview
Problem
Commercially available Li-ion battery separators face limitations in energy density, power density, safety, and thermal stability, with existing high-performance polymers like polyolefin-based microporous films not adequately addressing the need for high electrochemical stability, low self-discharge, and mechanical strength.
Innovation Solution
A porous separator comprising a nanoweb of fully aromatic polyimide nanofibers with a degree of imidization greater than 0.51, fabricated through electrospinning and imidization, is inserted between the cathode and anode to reduce self-discharge and variability in lithium-ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If polyethylene and/or polypropylene microporous membranes are used as battery separators, then good electrochemical stability is achieved, but thermal stability deteriorates as the membranes shrink at 120°C
Solution Approach 1:
The patent changes the material parameters by using fully aromatic polyimide instead of polyethylene/polypropylene, and specifically controls the degree of imidization to be greater than 0.51. This parameter change enables the separator to maintain dimensional stability at high temperatures (above 120°C) while preserving electrochemical stability, directly resolving the thermal shrinkage problem
Solution Approach 2:
The patent creates a composite structure by forming a nanoweb with specific nanofiber morphology from fully aromatic polyimide. The combination of the aromatic polyimide chemistry with the nanoweb physical structure achieves both high-temperature thermal stability and good electrochemical performance, resolving the contradiction between thermal and electrochemical stability
2Strength
If polyolefin based microporous films are used as separators, then good mechanical strength is achieved, but electrochemical stability and self-discharge performance deteriorate at high temperatures
Solution Approach 1:
The patent changes the polymer chemistry from polyolefin to fully aromatic polyimide with controlled imidization degree >0.51. This chemical parameter change provides both the mechanical strength needed for separator integrity and the electrochemical stability required for low self-discharge, even at elevated temperatures where polyolefins fail
Solution Approach 2:
The patent creates local quality differences through the nanoweb structure with specific nanofiber morphology. The nanoscale fiber structure provides mechanical strength through high surface area and inter-fiber bonding, while the fully aromatic polyimide chemistry provides electrochemical stability, achieving both requirements simultaneously
3Quantity of substance
If non-woven separators are used, then porosity and ion transport are improved, but mechanical strength deteriorates
Solution Approach 1:
The patent transitions from conventional microporous membrane structure to a three-dimensional nanoweb structure. This dimensional change allows the separator to achieve high porosity through the nanoscale fiber network while maintaining mechanical strength through the extensive surface area and inter-fiber bonding of the nanoweb architecture
Solution Approach 2:
The patent uses a thin nanoweb structure with flexible nanofibers that can conform to electrode surfaces while maintaining structural integrity. The nanoscale fiber diameter provides high porosity for ion transport, while the collective network of nanofibers maintains mechanical strength through distributed stress bearing
4Reliability
If separator materials are optimized for high electrochemical stability, then self-discharge is reduced, but thermal stability and mechanical strength deteriorate
Solution Approach 1:
The patent changes the material composition to fully aromatic polyimide with controlled imidization degree >0.51. This specific chemical parameter change achieves the optimal balance where the material exhibits low self-discharge (high electrochemical stability) while simultaneously maintaining thermal stability and mechanical strength at elevated temperatures
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 reduces self-discharge rate and variability in lithium-ion batteries by enhancing electrochemical stability, mechanical strength, and thermal stability, improving overall battery performance.
Implementation Method 1
The porous separator comprises a nanoweb that comprises a plurality of nanofibers wherein the nanofibers consist essentially of a fully aromatic polyimide... effectively reduces self-discharge rate and variability in lithium-ion batteries by enhancing electrochemical stability
Data Source
AI summary
A method for reducing the self discharge rate and the variability in the self discharge rate of an electrochemical cell wherein a porous separator is inserted between a cathode and an anode of the cell and the porous separator contains a nanoweb that comprises a plurality of nanofibers that may contain a fully aromatic polyimide and the fully aromatic polyimide has a degree of imidization of greater than 0.51 where degree of imidization is the ratio of the height of the imide C—N absorbance at 1375 cm−1 to the C—H absorbance at 1500 cm−1.