Polyimide Nanofiber Membrane Research Articles

Electrospun fine-diameter polyimide nanofiber membranes via metal wire-based needle-free technique for high-efficiency PM0.3 filtration at high-temperature

Polyimide (PI) nanofiber materials have garnered attention in the field of high-temperature filtration due to their exceptional thermal stability. Enhancing their filtration efficiency for fine particulate matter (PM2.5–0.3) and exploring their performance limits under high-temperature conditions are crucial for high-temperature filtration applications. In this study, a metal wire-based needle-free electrospinning technique was employed to electrospin polyimide (PI) material, successfully fabricating nanofiber membranes with an average fiber diameter of 122 nm within just 10 min at an elevated electrospinning voltage of 80 kV (electric field:333.33 kV/m). The Fine-diameter PI nanofiber membrane achieved a filtration efficiency of 99.99 % for PM0.3 and operated at a low resistance of 189.18 Pa. After continuous treatment at a high temperature of 390 °C for one hour, the Fine-diameter PI nanofiber membrane still maintained a filtration efficiency of 99.96 % for PM0.3 and was capable of completely filtering PM2.5. This demonstrates the excellent stability and reliability of the Fine-diameter PI nanofiber membrane under extreme temperature conditions. Additionally, the membrane exhibited outstanding hydrophobic properties, with a static contact angle of 130 ± 3°, aiding in maintaining its filtration performance in humid environments. The Fine-diameter PI nanofiber membrane developed in this study offers a novel fabrication strategy for PM filtration in high-temperature environments and provides new insights into its limit performance.

Cross-Linking Synergistic Effects to Enhance the Comprehensive Properties of Electrospun Polyimide Nanofiber Membranes for Advanced Lithium-Ion Batteries

Cross-Linking Synergistic Effects to Enhance the Comprehensive Properties of Electrospun Polyimide Nanofiber Membranes for Advanced Lithium-Ion Batteries

In-situ reinforced polyimide nanofiber membranes for highly efficient and safe lithium-ion batteries

Highly robust nanofibrous separators can effectively promote the battery's electrochemical performance and security. Here, we present a synergistically reinforced polyimide (PI) nanofiber membrane by tuning the regularity of PI chains while employing an in-situ PI reinforcement. The regularity of nanofibers and ordered region of PI chains is improved after hot stretching, thus enhancing the mechanical strength of PI nanofibers membrane. After synergistic PI-armor reinforcement, the reinforced PI nanofiber membrane with excellent thermotolerance and flame resistance exhibits a remarkable mechanical strength of 120.9 MPa, making them among the most robust PI nanofiber separators reported to date. Density functional theory calculations verify that the electron-rich sites of imide group in PI main chain can facilitate the desolvation of lithium-ion (Li+) and adsorb Li+ near imide groups of PI. Hence, the reinforced PI nanofiber separator with abundant 3D uniform nano-pore structure displays high ion conductivity (1.10 mS cm−1) and Li+ transfer number (0.58). Besides, Li symmetrical battery using the reinforced PI nanofiber membrane exhibits only a tiny voltage polarization during 300 h at 1.0 mA cm−2. These exceptional merits offer excellent specific capability (128.1 mA h g−1 at 5 C) to reinforced PI nanofiber membrane-based LIBs, along with 100-cycle battery stability at 1 C without significant capacity decay.

PI nanofiber membranes with pH-responsive wettability fabricated through solution blow spinning for efficient on-demand oil-water separation

Nanofiber membranes (NFMs) are widely used in oil-water separation area due to their unique structure and properties. However, achieving efficient and on-demand separation of oil-water mixtures using NFMs remains a challenge. Herein, we prepared polyimide nanofiber membranes (PI-NFMs) with fluffy structures through solution blow spinning (SBS), and the average diameter of the PI nanofibers was 506.1 ± 75.6 nm. The PI-NFMs exhibited excellent pH responsiveness, demonstrating the ability to swiftly convert their wetting properties between highly hydrophobic and superhydrophilic through a simple acid-alkali treatment. Additionally, the conversion between oil removing model and water removing model according to the type of oil-water mixture was realized. The performance of the membranes in separating oil and water was evaluated using five different densities of oil-water mixtures. Only driven by gravity, the membrane exhibits good separation efficiency and extremely high permeate fluxes with the water and oil fluxes to 37,641.84 and 71,083.16 L·m−2·h−1, respectively, which also shows decent reusability. This work presents a promising solution for the intelligent, efficient, and controllable treatment of industrial oil effluents and oil spills.

Flexible and MOF-808 uniformly assembled polyimide nanofiber membranes with excellent mechanical properties for rapid degradation of chemical warfare agents

Breathable and soft protective clothing with self-disinfection function is crucial for the practical application of protecting the human body from being killed by corrosive agents. Recent wars and terrorist attacks have motivated researchers to focus on efficient digestion materials as chemical warfare agents (CWAs). Zirconium-based metal–organic frameworks (Zr-MOFs) have been proven to efficiently digest CWAs. However, their powder form limits their application in personal protection. Uniformly and firmly anchoring Zr-MOFs onto fiber materials to form flexible protection fabrics remains a challenge. In this study, a polyimide nanofiber composite membrane loaded with MOF-808 with a cross-linked structure is prepared by combining electrospinning, thermal crosslinking, and the in-situ growth of pre-soaked Zr4+ seeds. The composite film shows excellent softness and mechanical properties with mechanical strength exceeds 20 MPa. Meanwhile, the uniform anchoring of the Zr-MOF on the fibers yields a high specific surface area (453 m2/g) of the composite membrane. In addition, the composite membrane can digest the mustard gas simulant, 2-chloroethyl ethyl sulfide, at a digestion efficiency of 90.9%. This simple and efficient solution provides a new method for the development of breathable, flexible, self-sterilizing materials, which are expected to be applied as protective materials against chemical warfare agents, for human body protection, and in other fields.

Fluorine-containing polyimide nanofiber membranes for durable and anti-aging daytime radiative cooling

Personal daytime radiative cooling (PDRC) materials have high sunlight reflection and high selective emissivity to outer space in the main atmospheric window, demonstrating huge potential in energy-saving for sustainable development. Recently, polymer-based membranes for radiative cooling have been widely reported, due to their easy processing, low cost, and unique optical performance. However, the desired high sunlight reflectance of PDRC materials is easily dampened by environmental aging, high temperature, and ultraviolet (UV) irradiation, resulting in reduced cooling performance for most polymers, adverse to large-scale practical applications. In this work, we demonstrate a novel polyimide nanofiber (PINF) membrane with a fluorine-containing structure via typical electrospinning technology. The resultant PINF membrane exhibits high sunlight reflectance, UV resistance, and excellent thermal stability, rendering anti-aging daytime radiative cooling. The sunlight reflectance of PINF membranes could maintain constant in the aging test for continuous 720 h under outdoor solar irradiation, exhibiting durable and long-term personal daytime radiative cooling performance.

Flexible three-axis tactile sensor based on double-layer electrospun polyimide nanofiber membrane

Flexible three-axis tactile sensor based on double-layer electrospun polyimide nanofiber membrane

In situ aluminide armored polyimide nanofiber separators with ultrahigh strength and high wettability for advanced lithium-ion batteries

Polyimide (PI) has been widely used in aerospace, electronic information, novel energy, and other industries due to its excellent high- and low-temperature, radiation, and chemical corrosion resistance. However, the use of electrospun PI separators in lithium-ion batteries (LIBs) is limited due to their poor electrolyte wettability and insufficient mechanical strength. Inorganic materials such as aluminide have typically been used in the coating composition of PI separators. To investigate the effects of different aluminide components, in this work, PI materials were prepared by the complexation–hydrolysis method and used as separators for LIBs. The physicochemical and electrochemical properties of the different nanofiber membranes were studied by adjusting the calcination temperature. The results showed that the sample with the highest tensile strength was 107.6 MPa, which is close to the commercial polyolefin separator. When the calcination temperature increased to 300 °C and then exceeded 400 °C, the aluminide shell initially transformed into thin boehmite and then into γ-Al2O3 phases. The mechanical properties of the nanofiber membranes were enhanced, and the wettability and electrochemical characteristics also improved to some extent. Furthermore, the nanofiber structure was destroyed at 500 °C and could not meet the long-term battery cycles. Therefore, when the calcination temperature was controlled between 300 °C and 400 °C, the aluminide-armored PI nanofiber membranes exhibited better comprehensive performance and were suitable for use as separators in LIBs, which was of great significance for improving the safety and stability of LIBs, especially power batteries.

Core–Shell Structured Polyimide@γ-Al2O3 Nanofiber Separators for Lithium-Ion Batteries

Owing to its excellent thermal stability, polyimide (PI) is regarded as one of the most promising alternatives among separators for high-safety lithium-ion batteries (LIBs). Unfortunately, the wettability of the PI separator to electrolytes is still undesirable. The complexation–hydrolyzation method was used to develop a composite membrane with a core–shell structure that anchors γ-Al2O3 nanoparticles on PI nanofiber (PI@γ-Al2O3) as an LIB separator. The effects of surface treatment on the physicochemical and electrochemical properties of PI composite membranes are studied in detail, using the pristine PI nanofiber membrane as a reference. The results show that the PI@γ-Al2O3 nanofiber membrane exhibits better physicochemical properties and electrochemical performances. Specifically, the wettability property of the PI@γ-Al2O3 nanofiber membrane is improved with an almost zero contact angle, which significantly meets the requirements of high-performance LIBs. Furthermore, the electrochemical performance of the PI@γ-Al2O3 nanofiber membrane also shows excellent comprehensive properties with the ionic conductivity improving from 0.81 to 1.74 mS cm–1. Besides, the PI@γ-Al2O3 nanofiber membrane maintains a long charge–discharge process with a capacity retention rate of 98% at 0.5 C after 100 cycles. Consequently, the aforementioned excellent performances illustrate that core–shell PI@γ-Al2O3 nanofiber membranes have a promising future for the safety and stability of LIBs.

Biomimetic Core-Shell-Structured Nanofiber Membranes for Rapid and Portable Water Purification.

Rapid and portable water purification (RPWP) technologies, helping travelers survive in the wild, have attracted increasing interest due to increasing activities, such as exploration, field hiking, and excursion. Field water is usually pathogenic because of various soluble and insoluble contaminants. In this study, fish-gill-like biomimetic core-shell-structured nanofiber membranes are designed and synthesized by an in situ oxidation polymerization coating process. A polyimide nanofiber membrane and a polypyrrole (PPy) coating layer are employed as a core and shell, respectively. The biomimetic membranes exhibit dual-functional capacities: a rapid removal of insoluble contaminants owing to the highly porous network and broad-spectrum adsorption of soluble contaminants enabled by the PPy shell. Model studies confirm the excellent ability of the membranes to purify Cr(VI)-contaminated water to drinkable water with a safe capacity of ∼1415 L m-2. Actual application tests show that the membrane can efficiently remove coliform and suspended solids in a muddy water sample taken from a river in Suzhou, China. This study provides a promising route for the design of a single-layer membrane with dual functions for highly efficient RPWP.

A Novel Triple Crosslinking Strategy on Carbon Nanofiber Membranes as Flexible Electrodes for Lithium-Ion Batteries.

In order to solve the problem of low electrical conductivity of carbon nanofiber membranes, a novel triple crosslinking strategy, including pre-rolling, solvent and chemical imidization crosslinking, was proposed to prepare carbon nanofiber membranes with a chemical crosslinking structure (CNMs-CC) derived from electrospinning polyimide nanofiber membranes. The physical-chemical characteristics of CNMs-CC as freestanding anodes for lithium-ion batteries were investigated in detail, along with carbon nanofiber membranes without a crosslinking structure (CNMs) and carbon nanofiber membranes with a physical crosslinking structure (CNMs-PC) as references. Further investigation demonstrates that CNMs-CC exhibits excellent rate performance and long cycle stability, compared with CNMs and CNMs-PC. At 50 mA g−1, CNMs-CC delivers a reversible specific capacity of 495 mAh g−1. In particular, the specific capacity of CNMs-CC is still as high as 290.87 mAh g−1 and maintains 201.38 mAh g−1 after 1000 cycles at a high current density of 1 A g−1. The excellent electrochemical performance of the CNMs-CC is attributed to the unique crosslinking structure derived from the novel triple crosslinking strategy, which imparts fast electron transfer and ion diffusion kinetics, as well as a stable structure that withstands repeated impacts of ions during charging and discharging process. Therefore, CNMs-CC shows great potential to be the freestanding electrodes applied in the field of flexible lithium-ion batteries and supercapacitors owing to the optimized structure strategy and improved properties.

High‐Performance Polyimide Nanofiber Membrane for Progressive and Safe Lithium‐Ion Batteries Guarded by a Zirconia Armor Layer

Superior separator: A flexible zirconia nanoshell@polyimide (ZrO2@PI) composite separator with a core-shell structure is prepared via an in situ absorption complexation and hydrolysis strategy for high-performance and safe lithium-ion batteries. This separator combines the advantages of the PI nanofiber and the ceramic ZrO2, exhibiting excellent flame retardance, wettability, and thermal stability, far better than commercial Celgard-2400 separator. Batteries assembled with this ZrO2@PI composite separator display a higher rate capability and capacity retention rate.

Ultra-robust polyimide nanofiber separators with shutdown function for advanced lithium-ion batteries

Safety issues have significantly impeded the development of modern lithium-ion batteries (LIBs), and fabricating advanced separators has been considered as a feasible solution to improve the security of LIBs. Here, we present an advanced polyimide (PI) nanofiber membrane (referred to as PIE) with ultrahigh strength and the shutdown function by optimizing precursor viscosity and nanofibers microstructure. Increasing chain length of the PI backbone and in -situ bonding technique can markedly promote mechanical properties of PI nanofiber separator (strength of pristine PI nonwoven >60 MPa, strength of modified PI nonwoven >90 MPa), which is a new record so far among current PI nanofiber membranes. The present PIE separator displayed superior wettability, heat-resistant, and ion conductivity compared to the commercial Celgard separator. Importantly, the excellent flame resistance and high-temperature shutdown function of PIE separators ensure the security of LIBs. Based on our rational separator design, the PIE separators possessed higher LIB capability (111.3 mAh g −1 at 10 C) than the Celgard separator (90.8 mAh g −1 at 10 C). Moreover, the PIE separator-based LIBs can run stably at 1 C and 5 C for 100 cycles. The present work demonstrated the likelihood of replacing the commercial polyolefin separator with the advanced PI nanofiber membranes. • Advanced PIE separators are prepared by increasing chain length of PI backbone and using in -situ bonding technique. • The strength of as-fabricated PI separators present a highest record so far (pristine PI nonwoven >60 MPa, modified PI nonwoven >90 MPa). • The excellent thermostability, flame resistance, and shutdown function can ensure the safety of LIBs. • PIE separators exhibit superior LIB capability and cycling stability.

Controllable Coaxial Coating of Boehmite on the Surface of Polyimide Nanofiber Membrane and Its Application as a Separator for Lithium‐Ion Batteries

With the continuous development of lithium‐ion batteries (LIBs), the electrochemical performance and safety of LIBs have become increasingly challenged recently. Therefore, research on high‐performance LIB separators has gradually attracted widespread attention. As an important component of lithium batteries, the diaphragm plays an important role in battery safety. Improving battery separator performance is an important way to improve batteries’ safety and electrochemical performance. Herein, to prepare a new type of LIB separator, a preparation strategy in which polyimide (PI) nanofibers can be coaxially encapsulated by the inorganic boehmite (AlOOH) ceramics through an adsorption and complexation process is developed. This strategy involves immersing partially imidized PI nanofiber membranes into anhydrous aluminum chloride ethanol solution and dilute ammonia, where the adsorption−complexation and hydrolysis processes are completed. During the hydrolysis process, the PI nanofibers are evenly coated with AlOOH. The amount of AlOOH can be controlled easily by adjusting the concentration of the anhydrous aluminum chloride ethanol solution. After being encapsulated with AlOOH, the separator exhibits better mechanical properties, wettability, thermal stability, cycling durability, and a high capacity, along with faster ion transport speed. All excellent features prove that the PI@AlOOH composite nanofiber membrane is an advanced high‐performance LIB separator.

ZIF-8/PI Nanofibrous Membranes With High-Temperature Resistance for Highly Efficient PM0.3 Air Filtration and Oil-Water Separation.

Air and water pollution poses a serious threat to public health and the ecological environment worldwide. Particulate matter (PM) is the major air pollutant, and its primary sources are processes that require high temperatures, such as fossil fuel combustion and vehicle exhaust. PM0.3 can penetrate and seriously harm the bronchi of the lungs, but it is difficult to remove PM0.3 due to its small size. Therefore, PM0.3 air filters that are highly efficient and resistant to high temperatures must be developed. Polyimide (PI) is an excellent polymer with a high temperature resistance and a good mechanical property. Air filters made from PI nanofibers have a high PM removal efficiency and a low air flow resistance. Herein, zeolitic imidazolate framework-8 (ZIF-8) was used to modify PI nanofibers to fabricate air filters with a high specific surface area and filtration efficiency. Compared with traditional PI membranes, the ZIF-8/PI multifunction nanofiber membranes achieved super-high filtration efficiency for ultrafine particles (PM0.3, 100%), and the pressure drop was only 63 Pa. The filtration mechanism of performance improvement caused by the introduction of ZIF-8/PI nanofiber membrane is explored. Moreover, the ZIF-8/PI nanofiber membranes exhibited excellent thermal stability (300 C) and efficient water–oil separation ability (99.85%).

Enhanced thermal insulation properties of PI nanofiber membranes achieved by doping with SiO2 nanoparticles

At present, energy consumption is a worldwide topic and it is an urgent requirement for the development of energy-saving materials. Thermal insulation materials with a low thermal conductivity show a significant potential to reduce energy waste. In this study, polyimide (PI) and silica/polyimide (SiO2/PI) nanofiber membranes (NFMs) with low thermal conductivity were prepared by electrospinning. The effect of different content of SiO2 nanoparticles (SiO2 NPs) on the thermal insulation properties of PI NFMs and the thermal insulation mechanism were studied. SiO2/PI NFMs has the lowest thermal conductivity of 0.033 W/(m·K) when the content of SiO2 NPs was 2 wt%. The experimental results reveal that when the addition of SiO2 NPs was low, the dominant factor of the increasing thermal insulation is the interfacial thermal contact resistance between the SiO2 NPs and PI nanofibers. Moreover, the SiO2 NPs can improve the thermal stability and hydrophobic of SiO2/PI NFMs. This study indicates the SiO2/PI NFMs has the potential applications in thermal insulation.

Electrospun Poly[poly(2,5-benzophenone)]bibenzopyrrolone/polyimide nanofiber membrane for high-temperature and strong-alkali supercapacitor

The separator is an important component for energy storage devices. At present, the membranes for supercapacitors are rare, especially the ones that work with an alkaline electrolyte. Herein, a type of flexible and highly porous polymer hybrid nanofiber membrane was prepared via a facile electrospinning process and served as a separator for supercapacitor’s work with strong alkaline electrolyte. As obtained, poly[poly(2,5-benzophenone)]bibenzopyrrolone/polyimide (PBPY/PI) membrane showed good thermal stability, high mechanical strength, large electrolyte uptake (452%), and fast ion conductivity (0.68 mS/cm). Moreover, PBPY/PI membrane exhibited excellent alkali resistance. The supercapacitor assembled with PBPY/PI membrane showed much better performance than those assembled with a commercial polypropylene membrane and electrospun polyimide nanofiber membrane and was found without capacitance loss after charge/discharge at 30 A/g for 10,000 cycles at 80 °C. The PBPY/PI membrane is a good candidate with temperature resistance and alkali resistance for high-performance supercapacitors.

Enhanced the mechanical strength of polyimide (PI) nanofiber separator via PAALi binder for lithium ion battery

Polyimide (PI) nanofiber membrane prepared by electrospinning technique exhibits poor mechanical strength for the slippage of fibers, which limits it applied into lithium ion battery (LIB). In this study, we are devoted to promoting the macro mechanical strength of PI nanofiber membrane by inhibiting the slippage among the fibers. Lithium polyacrylate (PAALi) is a kind of excellent binder, and it contributes to increasing the adhesion effect between the fibers. As a result, the PI nanofiber membrane treated by PAALi solution shows the mechanical strength of 16.1 MPa, higher than 5.0 MPa of pristine PI membrane. The introduction of this binder makes the originally loose and disordered PI nanofibers cross-link with each other and prevents from the slip between the fibers. Surprisingly, the PAALi binder has no effect on the thermal stability and electrochemical performance of PI nanofiber separator. Furthermore, these LiCoO2/Li cells using the modified PI nanofiber separators exhibit better cycling stability and superior rate performance compared with the cells containing pristine PI separators. It demonstrates that the use of PAALi binder is a promising method to improve the mechanical strength of nanofiber membrane, which gets it applied in the high-power LIB.

Effect of the heat treatment temperature on mechanical and electrochemical properties of polyimide separator for lithium ion batteries

In order to solve the shortcomings of the current traditional commercial polyolefin microporous membranes with worse thermostability at high temperature, polyimide (PI) nanofiber membranes prepared by electrospinning are promising separators for lithium ion batteries that operate at high temperatures. This preparation includes the forming process of poly(amic acid) (PAA) fibers membrane and thermal-imidization process. In this study, we design the experiment of thermal-imidization for PAA fibers to improve the mechanical strength and the electrochemical performance of the obtained PI nanofiber membrane. It is found that the degradation phenomenon and the crosslinking function occur after the imidization during the heat treatment. The mechanical strength of PI nanofiber membrane gets improved with new crosslinking system after being heat-treated at 350 °C. LiCoO2/Li cells based on such PI nanofiber membranes exhibit excellent cycle performance (300 cycles) and rate performance (even at high rates of 6 C), better than those employing polyolefin microporous membranes. During the heat treatment of polyamic acid, a thermal imidization process will occur. At the same time, different heat treatment temperatures will lead to differences in the degree of imidization and the structure of the fiber membrane material. It is important to understand the thermal imidization process. The effect of thermal imidization temperature on the performance of the electrospun polyimide lithium ion battery separator is studied. The experimental results show that although the degree of imidization is decreased by the heat treatment at 350 °C, it has better cycle performance (300 circles) and rate performance (even at high rates of 6 C).

A flexible capacitive pressure sensor based on an electrospun polyimide nanofiber membrane

A flexible capacitive pressure sensor based on electrospun polyimide (PI) nanofiber membrane as a dielectric layer has been proposed to improve its performance including sensitivity, detection limit and response speed due to its loose structures. An electrospun PI nanofiber membrane, a commercial PI tape and a PDMS membrane as dielectric layer had been tested and diverse thicknesses of PI nanofiber membranes were explored to optimize the dielectric layer. The sensor with such a dielectric layer exhibited high sensitivity (2.204 kPa−1 at 3.5–4.1 Pa), wide scale range (0–1.388 MPa), low detection limit (3.5 Pa) and good cyclic stability (>10,000 cycles). A typical 4 × 4 sensor array could not only accurately sense corresponding force, but also identify the slide of force by monitoring dynamic capacitive changes of elements.