Polyimide Blend Nanofibers for Battery Separators
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Solution Overview
Problem
Current lithium ion battery separators, such as polyethylene and polypropylene, fail to ensure integrity at high temperatures and are prone to thermal runaway due to shrinkage, limiting their safety and application in high-capacity and high-power applications like automobile power.
Innovation Solution
Development of high-temperature-resistant and high-porosity polyimide blend nanofibers created through electrostatic spinning and high-temperature imidization of a bicomponent polyimide precursor, combining a non-meltable and meltable polyimide precursor to achieve enhanced mechanical strength, porosity, and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional separators like polyethylene or polypropylene are used, then the battery can be manufactured with standard materials and processes, but the separator fails to maintain integrity at high temperatures and is prone to thermal runaway due to shrinkage
Solution Approach 1:
The patent changes the material parameters by using polyimide instead of conventional polyethylene or polypropylene separators. Polyimide has inherently higher thermal stability with decomposition temperature above 500°C, preventing the thermal runaway that occurs with conventional materials at elevated temperatures.
Solution Approach 2:
The patent employs a bicomponent polyimide blend system combining two different polyimide precursors (one meltable at 300-400°C and one non-meltable at high temperature). This composite approach allows the material to exhibit both good processing characteristics and exceptional high-temperature resistance, resolving the contradiction between manufacturability and thermal stability.
2Reliability
If high-temperature-resistant materials are used to prevent thermal runaway, then safety is improved, but mechanical strength and porosity may be compromised
Solution Approach 1:
The bicomponent polyimide blend combines a meltable precursor (providing good mechanical strength and processability) with a non-meltable high-temperature-resistant precursor. The synergistic effect of this composite material system achieves both high mechanical strength (10-50 MPa) and exceptional high-temperature resistance without compromising either property.
Solution Approach 2:
The patent creates different functional zones within the separator structure through the bicomponent blend. The meltable component provides structural integrity and mechanical strength in the bulk, while the non-meltable component ensures high-temperature stability and prevents shrinkage at critical locations during thermal events.
3Reliability
If high-temperature-resistant materials are used, then thermal stability is improved, but porosity may be reduced leading to overhigh internal resistance
Solution Approach 1:
The bicomponent polyimide blend system maintains high porosity (above 75%) while achieving exceptional thermal stability. The combination of meltable and non-meltable precursors creates a porous network structure that allows efficient ion transport, preventing high internal resistance while ensuring high-temperature resistance.
Solution Approach 2:
The patent specifically designs the separator as a porous nanofiber membrane with porosity above 75%. This porous structure is achieved through the electrostatic spinning process and is maintained in the final polyimide blend product, ensuring low internal resistance and good electrolyte penetration while the polyimide composition provides thermal stability.
4Area of stationary object
If electrostatic spinning is used to create nanofibers, then porosity and surface area are improved, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The patent optimizes the electrostatic spinning parameters including voltage (15-30 kV), distance (100-300 mm), and receiving drum speed (50-200 rpm) to achieve consistent nanofiber production with controlled porosity above 75% and fiber diameters of 50-1000 nm. The bicomponent precursor formulation is specifically designed to work with these spinning parameters.
Solution Approach 2:
The patent performs preliminary blending of the two polyimide precursors in the solution state before electrostatic spinning. This pre-mixing ensures homogeneous distribution of both components in the spinning solution, which simplifies the subsequent spinning process and ensures consistent material properties in the final product without requiring complex post-processing.
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 resulting polyimide blend nanofibers exhibit excellent resistance to high temperatures, thermal shrinkage, and chemical corrosion, with characteristics like fiber diameters of 50-1000 nm, decomposition temperatures above 500°C, and mechanical strengths of 10-50 MPa, making them suitable for safe battery and supercapacitor separators in high-capacity and high-power applications.
Implementation Method 1
the polyimide blend nanofibre is manufactured by subjecting a precursor of two polyimides to high-voltage electrostatic spinning
Implementation Method 2
a high-temperature imidization treatment, and the polyimide blend precursor is converted into a bicomponent polyimide blend by high temperature imidization
Data Source
AI summary
A polyimide blend nanofiber and its use in battery separator are disclosed. The polyimide blend nanofiber is made of two kinds of polyimide precursors by high pressure electrostatic spinning and then high temperature imidization processing, wherein one of the polyimide precursor does not melt under high temperature, and the other is meltable at a temperature of 300-400° C. The polyimide blend nanofiber of present invention has high temperature-resistance, high chemical stability, high porosity, good mechanical strength and good permeability, and can be applied as battery separator.