Recent Advances in Electrospun Sustainable Composites for Biomedical, Environmental, Energy, and Packaging Applications.

Electrospinning has gained constant enthusiasm and wide interest as a novel sustainable material processing technique due to its ease of operation and wide adaptability for fabricating eco-friendly fibers on a nanoscale. In addition, the device working parameters, spinning solution properties, and the environmental factors can have a significant effect on the fibers\u27 morphology during electrospinning. This review summarizes the newly developed principles and influence factors for electrospinning technology in the past five years, including these factors\u27 interactions with the electrospinning mechanism as well as its most recent applications of electrospun natural or sustainable composite materials in biology, environmental protection, energy, and food packaging materials

Poly(methyl methacrylate) reinforced poly(vinylidene fluoride) composites electrospun nanofibrous polymer electrolytes as potential separator for lithium ion batteries

Fabrication of nanofibrous polymer electrolyte membranes of poly(vinylidene fluoride) (PVdF) and poly(methyl methacrylate) (PMMA) in different proportion (PVdF:PMMA = 100:0, 80:20 and 50:50) by electrospinning is reported to investigate the influence of PMMA on lithium ion battery performance of PVdF membrane as separator. As-fabricated polymer electrospun nanofibrous membranes were characterized by SEM, FTIR, XRD, TGA and DSC for morphology, structure, crystallinity and thermal stability. PVdF–PMMA (50:50) polymer electrolyte membrane showed ionic conductivity 0.15 S/cm and electrolyte uptake 290% at room temperature. After 50 cycles, the discharge capacity 140 mAh/g of Li/PE/LiFePO4 cells with PVdF–PMMA (50:50) as polymer electrolyte (PE) membrane was found to be retained around 93.3%. The electrolyte uptake, ionic conductivity, and discharge capacity retention were improved by optimizing the proportion of PMMA in PVdF. Nanofibrous PVdF–PMMA (50:50) polymer electrolyte membrane was found to be a potential separator for lithium ion batteries

Functional applications of electrospun nanofibers

With the rapid development of nanoscience and nanotechnology over the last two decades, great progress has been made not only in preparation and characterization of nanomaterials, but also in their functional applications. As an important one-dimensional nanomaterial, nanofibers have extremely high specific surface area because of their small diameters, and nanofiber membranes are highly porous with excellent pore interconnectivity. These unique characteristics plus the functionalities from the polymers themselves impart nanofibers with many desirable properties for advanced applications

Electrospun MXene/polyimide nanofiber composite separator for enhancing thermal stability and ion transport of lithium-ion batteries

Safety of lithium-ion batteries (LIBs) has garnered significant attention. As an essential component of batteries, the separator plays a crucial role in separating the positive and negative electrodes, preventing short circuits, and allowing ion transport. Therefore, it is necessary to develop a high-performance separator that is both thermally stable and capable of rapid Li+ transport. Polyimide (PI) is a material with high thermal stability, but low electrolyte wettability and high interfacial resistance of PI restrict its application in high-performance LIBs batteries. MXene possesses excellent mechanical properties and good electrolyte affinity. PI/MXene nanofiber composite separator. Combines the high thermal stability of PI with the superior electrolyte wettability of MXene. It exhibits a high tensile strength of 19.6 MPa, low bulk resistance (2.5 Ω), and low interfacial resistance (174 Ω), as well as a low electrolyte contact angle of 29°, while retaining the high-temperature resistance and flame retardancy of PI. Batteries assembled with this composite separator demonstrated a specific capacity of 111.0 mAh g−1 and a capacity retention rate of 66% at 2C. In long-term cycling tests of LiFePO₄ half-cells at 1C, after 200 charge-discharge cycles, the PI/MXene battery showed a discharge specific capacity of 126.7 mAh g−1 and a capacity retention rate of 91%. Additionally, the battery operated normally at 120°C. The composite separator, by integrating the high thermal stability of PI with the excellent electrolyte wettability and conductivity of MXene, demonstrates significant advantages in enhancing battery safety and cycling performance. Through this composite structure can provide a more reliable and safe solution for high-performance LIBs

Polypyrrole-based Nanofibrous Membrane Separator for Lithium-ion Battery

A battery separator is one of the key components of a Lithium-ion battery (LIB). It serves as an insulator between the electrodes to prevent the internal short circuit. More importantly, the battery separator retains liquid electrolyte within its porous structure, allowing the migration of lithium ions during battery cycling. The fast-growing demand for high-performance LIBs in various applications requires the development of superior separators. Electrospun nanofibrous separator receives considerable attention among all the progresses of battery separator research. Generally, electrospun nanofibrous separator offers appealing features including large pore size (typically above 500 nm), high porosity (typically above 70%) and interconnected porous structure. This improves ions transportation efficiency and battery cycling performance. However, most studies are focused on electrochemical inert material as battery separator, which is incapable of contributing any battery capacity to the LIB cells. This thesis study develops a redox-active separator based on electrospun polypyrrole (PPy) composite nanofibers to enhance battery capacity. The proposed separator is fabricated by in-situ polymerization of PPy onto electrospun polyacrylonitrile (PAN) nanofibers followed by subsequent electrospinning to form a bilayer membrane. This thesis starts with understanding the separator’s effects on the battery performances to provide insights and guidance to the separator design. A two-dimensional electrochemical-thermal coupled model is developed for a 38120-type LiFePO4 LIB. The model results show that separator thickness strongly impacts battery energy density. In addition, the mass transfer resistance of the separator increases with decreasing separator porosity, which results in increased electrolyte concentration gradient. However, the correlation between separator porosity and electrolyte concentration gradient indicates that a separator porosity of 80% or greater contributes little to the resistance to mass transfer. After that, a detailed study of the kinetics on the in-situ polymerization of PPy with electrospun fibrous membrane as the template is carried out to better understand the mechanisms behind the fabrication of the proposed separator. The in-situ polymerizations of PPy are produced on electrospun fibrous PAN templates at temperatures ranging from 273 to 285 K. The experimental results show that the overall reaction rate of the in-situ polymerization process in the presence of electrospun fibrous template is faster than that without template. Further investigation confirms that the increase in the overall reaction rate results from the enhanced reactions between oxidized pyrrole oligomers and neutral pyrrole monomers Then, the proposed separator with expected properties is fabricated and characterized. The produced separator exhibits a bi-layer structure, including a layer of PAN@PPy core-shell structured fibers and another layer of PAN fibers. The porosity and electrolyte uptake of the redox-active separator (79.3±7.1% and 294.6±31.5%) are much higher than that of a commercial PP separator (41% and 81.5±17.4%). In addition, the redox-active separator is thermally stable up to 250 ℃ and capable of maintaining its dimensions at 160 ℃. Moreover, the redox-active separator exhibits superb mechanical properties than the electrospun PAN separator dose. Finally, the separators are assembled into separate LIB cells for performance evaluation. The battery cell containing redox-active separator exhibits the highest discharge capacity of 158.7-227.0 mAh∙g-1 at different current rates of 2-0.2 C. The enhanced battery capacity stems from the redox-activity of the PPy polymer contained in the redox-active separator. In addition, the battery cell with redox-active separator achieves the highest gravimetric energy density of 103.0 mAh∙g-1, which is 56.1% higher than that with the commercial PP separator. These results suggest a promising strategy to enhance the capacity of LIBs by merely modifying the conventional separators into nanofibrous redox-active separators

Recent Progress in Biopolymer-Based Hydrogel Materials for Biomedical Applications.

Hydrogels from biopolymers are readily synthesized, can possess various characteristics for different applications, and have been widely used in biomedicine to help with patient treatments and outcomes. Polysaccharides, polypeptides, and nucleic acids can be produced into hydrogels, each for unique purposes depending on their qualities. Examples of polypeptide hydrogels include collagen, gelatin, and elastin, and polysaccharide hydrogels include alginate, cellulose, and glycosaminoglycan. Many different theories have been formulated to research hydrogels, which include Flory-Rehner theory, Rubber Elasticity Theory, and the calculation of porosity and pore size. All these theories take into consideration enthalpy, entropy, and other thermodynamic variables so that the structure and pore sizes of hydrogels can be formulated. Hydrogels can be fabricated in a straightforward process using a homogeneous mixture of different chemicals, depending on the intended purpose of the gel. Different types of hydrogels exist which include pH-sensitive gels, thermogels, electro-sensitive gels, and light-sensitive gels and each has its unique biomedical applications including structural capabilities, regenerative repair, or drug delivery. Major biopolymer-based hydrogels used for cell delivery include encapsulated skeletal muscle cells, osteochondral muscle cells, and stem cells being delivered to desired locations for tissue regeneration. Some examples of hydrogels used for drug and biomolecule delivery include insulin encapsulated hydrogels and hydrogels that encompass cancer drugs for desired controlled release. This review summarizes these newly developed biopolymer-based hydrogel materials that have been mainly made since 2015 and have shown to work and present more avenues for advanced medical applications

A facile blow spinning technique for green cellulose acetate/polystyrene composite separator for flexible energy storage devices

projects LA/P/0037/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. This work was also supported by ERC-CoG-2014. The authors would also like to thank João Lopes for his contribution with the home-made mechanical abrasion setup. Publisher Copyright: © 2023 The Author(s)The search of sustainable gadgets, such as the portable electronics and wearables, have sparked the need for more sustainable and environment friendly constituent elements (e.g., electrode materials, separators, and green electrolytes) and low-cost scalable fabrication techniques. Herein, a facile and scalable blow spinning technique is proposed for the synthesis of a cellulose-based separator for flexible energy storage devices. A cellulose acetate and polystyrene (CA:PS) based composite separator is synthesized for the first time for flexible supercapacitors by exploiting the blow spinning technique. Different combinations of CA:PS were synthesized, and electrochemical performances of the devices were evaluated. A sweat simulation solution is used as green electrolyte for the development of symmetrical carbon yarn-based supercapacitors. The influence on the device performances of pristine carbon yarn, activated carbon yarns and PEDOT functionalized carbon yarns, electrodes were compared. Specific capacitances of 2.8 Fg−1 and 33 Fg−1 were obtained for pristine carbon and PEDOT functionalized carbon fibers respectively. The fabricated devices exploiting the composite separator exhibited good washing stability up to 30 cycles and capacitance retention of 95% up to 1000 charge/discharge cycles.publishersversionpublishe

Enhancing Mechanical Strength of Electrospun Nanofibers by Thermal Crosslinking and Coaxial Electrospinning

Electrospinning of nonwoven nanofibrous mats has received significant attention in recent years due to the high versatility and porosity of electrospun mats. Specifically, considerable interest has developed in using electrospun nanofiber mats as breathable dressing layers, separator layers in lithium-ion batteries, etc. For example, the high porosity and high pore interconnectivity of nanofiber mats allows them to exhibit superior electrochemical characteristics and high overall battery performance. However, electrospun mats generally suffer from poor mechanical strength, creating the risk of a short circuit if a rip or tear were to appear. Many methods exist to improve the mechanical strength of electrospun nanofiber mats. Composite structures, such as multilayer or coaxial mats, can be used to improve the average mechanical strength of the fibers, while post-treatments can be used to improve the inter-fiber bonding to increase mechanical strength. However, many of these techniques impact the complexity and scalability of electrospinning or impact physical properties such as porosity. Alternatively, thermal crosslinking of fibers by heat treatment has emerged as a simple, scalable method of significantly improving mechanical strength, but typically results in considerable shrinkage. In this work, coaxial electrospinning is combined with thermal treatment to produce a novel method of improving the mechanical strength of nanofiber mats, without incurring significant dimensional shrinkage. Coaxial PAN/PVDF-HFP mats showed no significant shrinkage when tested at temperatures up to 240 ºC for 20 minutes, compared to the homogenous PVDF-HFP mats, which displayed a shrinkage of 94% when treated at 190 ºC for 20 minutes. When treated at 178 ºC for up to 30 minutes, the coaxial fibers consistently showed changes in thickness of less than 10% and no significant change in area. More importantly, the reductions in thickness and volume experienced by the coaxial mats were much more uniform across the varied treatment times when compared to those of the homogenous PVDF-HFP samples. The as-spun coaxial fibers showed a decrease in porosity compared to homogenous PVDF-HFP (95% to 79%) but remained much more porous than the commercial PP separator (41%). In addition, no significant change in average porosity in the coaxial samples occurred following treatment at 178 ºC for 20 minutes. Coaxial samples heat treated at 178 ºC for 5 minutes demonstrated a mechanical strength of 7.72 MPa, a 22% increase when compared to the as-spun coaxial fibers, and a 54% increase compared to the as-spun homogenous PVDF-HFP. Elongation at break decreased from 17.8% to 5.3% following the 5-minute heat treatment, showing a significant reduction compared to the elongation at break for as-spun PVDF-HFP (79.7%), and PVDF-HFP treated at 178 ºC for 5 minutes (40.6%). Therefore, the proposed technique of combining heat treatment with coaxial morphologies demonstrates significant potential for improving mechanical strength without dimensional shrinkage

Flexible, Heat-Resistant, and Flame-Retardant Glass Fiber Nonwoven/Glass Platelet Composite Separator for Lithium-Ion Batteries

A new type of high-temperature stable and self-supporting composite separator for lithium-ion batteries was developed consisting of custom-made ultrathin micrometer-sized glass platelets embedded in a glass fiber nonwoven together with a water-based sodium alginate binder. The physical and electrochemical properties were investigated and compared to commercial polymer-based separators. Full-cell configuration cycling tests at different current rates were performed using graphite and lithium iron phosphate as electrode materials. The glass separator was high-temperature tested and showed a stability up to at least 600 °C without significant shrinking. Furthermore, it showed an exceptional wettability for non-aqueous electrolytes. The electrochemical performance was excellent compared to commercially available polymer-based separators. The results clearly show that glass platelets integrated into a glass fiber nonwoven performs remarkably well as a separator material in lithium-ion batteries and show high-temperature stability