Combining polymeric membranes with inorganic woven fabric: Towards the continuous and affordable fabrication of a multifunctional separator for lithium-ion battery

Development of AlN-loaded PET separators from waste water bottle plastics with superior thermal characteristics for next-generation lithium-ion batteries

Preventing short circuit hazard due to lithium (Li) dendrite formation across a separator from the anode of a lithium-ion battery (LIB) throughout operation is important; however, conventional separator materials cannot fulfil the increasing safety standards of next-generation LIBs. Thus, developing separator materials with high Li dendrite suppression ability in order to prevent short circuit is of paramount importance for realising next-generation LIBs. In this study, aluminum nitride-loaded polyethylene terephthalate (PET/AlN) composites with micro-/nanoarchitecture were synthesized using PET that was recycled from commercial waste bottles via an electrospinning strategy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) suggested that AlN nanoparticles were encapsulated in PET micro-/nanoarchitecture fibres. Thermogravimetric analysis indicated that the AlN content in the composite materials was about 4-5 wt%. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy confirmed the PET polymer structure of PET/AlN composites. The PET/AlN 4 wt% separator exhibited a porosity of 69.23%, according to the n-butanol uptake test, and a high electrolyte uptake of 521.69%. Most importantly, electrochemical results revealed that when evaluated at a current density of 0.5C, PET/AlN 4 wt% composites could deliver a reversible specific capacity of 238.2 mA h g-1 after 100 cycles. When C-rate capability tests were conducted at high charge-discharge densities of 0.2, 0.5, 1, 2, and 4C, the PET/AlN 4 wt% composite manifested average specific capacities of about 225.3, 218.4, 191.0, 127.5, and 28.1 mA h g-1, respectively. The excellent electrochemical performance of the PET/AlN 4 wt% composite could probably be attributed to the combined benefits of AlN nanoparticles and the micro-/nanoarchitecture. These unique features of PET/AlN were advantageous for effective Li ion transport in repeated charge-discharge cycles and strong hydrothermal stability, thereby resulting in safety, high capacity and excellent C-rate performance. Overall, this study demonstrated the excellent electrochemical performance of PET/AlN composites as stable separator materials for advanced LIBs.

Clay-Originated Two-Dimensional Holey Silica Separator for Dendrite-Free Lithium Metal Anode

Lithium metal anode is the ultimate choice to obtain next-generation high-energy-density lithium batteries, while the dendritic lithium growth owing to the unstable lithium anode/electrolyte interface largely limits its practical application. Separator is an important component in batteries and separator engineering is believed to be a tractable and effective way to address the above issue. Separators can play the role of ion redistributors to guide the transport of lithium ions and regulate the uniform electrodeposition of Li. The electrolyte wettability, thermal shrinkage resistance, and mechanical strength are of importance for separators. Here, clay-originated two-dimensional (2D) holey amorphous silica nanosheets (ASN) to develop a low-cost and eco-friendly inorganic separator is directly adopted. The ASN-based separator has higher porosity, better electrolyte wettability, much higher thermal resistance, larger lithium transference number, and ionic conductivity compared with commercial separator. The large amounts of holes and rich surface oxygen groups on the ASN guide the uniform distribution of lithium-ion flux. Consequently, the Li//Li cell with this separator shows stable lithium plating/stripping, and the corresponding Li//LiFePO4 , Li//LiCoO2, and Li//NCM523 full cells also show high capacity, excellent rate performance, and outstanding cycling stability, which is much superior to that using the commercial separator.

Composite Membrane Containing Titania Nanofibers for Battery Separators Used in Lithium-Ion Batteries

In order to improve the electrochemical performance of lithium-ion batteries, a new kind of composite membrane made using inorganic nanofibers has been developed via electrospinning and the solvent-nonsolvent exchange process. The resultant membranes present free-standing and flexible properties and have a continuous network structure of inorganic nanofibers within polymer coatings. Results show that polymer-coated inorganic nanofiber membranes have better wettability and thermal stability than those of a commercial membrane separator. The presence of inorganic nanofibers in the polymer matrix enhances the electrochemical properties of battery separators. This results in lower interfacial resistance and higher ionic conductivity, leading to the good discharge capacity and cycling performance of battery cells assembled using polymer-coated inorganic nanofiber membranes. This provides a promising solution via which to improve conventional battery separators for the high performance of lithium-ion batteries.

Effect of Cross-Linking and Surface Treatment on the Functional Properties of Electrospun Polybenzimidazole Separators for Lithium Metal Batteries

In this work, electrospun PBI separators with a highly porous structure and nanofiber diameter of about 90-150 nm are prepared using a multi-nozzle under controlled conditions for lithium metal batteries. Cross-linking with α, α-dibromo-p-xylene and surface treatment using 4-(chloromethyl) benzoic acid successfully improve the electrochemical as well as mechanical properties of the separators. The resulting separator is endowed with high thermal stability and excellent wettability (1080 to 1150%) with commercial liquid electrolyte than PE and PP (Celgard 2400) separators. Besides, attractive cycling stability and rate capability in LiFePO₄/Li cells are attained with the modified separators. Prominently, CROSSLINK PBI exhibits a stable Coulombic efficiency of more than 99% over 100 charge-discharge cycles at 0.5 C, which is superior to the value of cells using commercial PE and PP (Celgard 2400) separators. The half cells assembled using the CROSSLINK PBI separator can deliver a discharge capacity of 150.3 mAh g^-1 at 0.2 C after 50 cycles corresponding to 88.4% of the theoretical value of LiFePO₄ (170 mAh g^-1). This work offers a worthwhile method to produce thermally stable separators with noteworthy electrochemical performances which opens new possibilities to improve the safe operation of batteries.

Stable Sodium-Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment

Sodium (Na) is the most appealing alternative to lithium as an anode material for cost-effective, high-energy-density energy-storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large-scale practical implementation of Na-metal batteries (SMBs) in commonly used and low-cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well-ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion-redistributors to self-orientate/homogenize the flux of Na-ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long-term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm^-2 , ≥700 h at 5 mA cm^-2 ) of symmetric cells are achieved in additive-free carbonate electrolytes. Moreover, the corresponding sodium-organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low-cost, and safe-credible SMBs, which could be readily extended to other alkali-metal batteries.

Enhanced air filtration performances by coating aramid nanofibres on a melt-blown nonwoven

Nanofibre membranes with a small diameter and a large specific surface area are widely used in the filtration field due to their small pore size and high porosity. To date, aramid nanofibres (ANFs) have received extensive research interest because of their high stiffness and excellent temperature resistance. However, the preparation of ANFs usually takes a long time, which greatly hampers the practical application of these fibres. Herein, we report the preparation of ANFs by a modified deprotonation method at elevated temperature. Owing to the increase of temperature, the preparation cycle of ANFs was shortened to 8 hours. The resulting ANF dispersion was further coated on a polypropylene melt-blown nonwoven to form a composite nonwoven filter. With the submicron porous structure, the filtration efficiency, pressure drop and quality factor of the filter were 95.61%, 38.22 Pa and 0.082 Pa^-1, respectively. Compared to the pristine nonwoven, the filtration, mechanical, and heat insulation properties of the composite filter were also significantly improved. This work may offer a simple and efficient way for enhancing the air filtration performances of current filters.

Analysis of Thermal-Mechanical Properties of Silicon Dioxide/Polyvinylidene Fluoride Reinforced Non-Woven Fabric (Polypropylene) Composites

In this paper, solution casting method is used to prepare the PP (polypropylene) non-woven fabric based composite film filled with silicon dioxide/polyvinylidene fluoride (SiO₂/PVDF). The mechanical and thermodynamic properties of PP/SiO₂/PVDF composites were studied by a uniaxial tensile test under different temperature and combustion experiment. It is found that the stress of PP/SiO₂/PVDF composite film with 4 wt % SiO₂ is the maximum value, reaching 18.314 MPa, 244.42% higher than that of pure PP non-woven. Meanwhile, the thermal–mechanical coupling tests indicate that with the increase of temperature, the ultimate stress and strain of the composite decrease. At the same time, the thermal shrinkage property of the composite during the heating process is studied. The modified composite has good thermal stability under 180 °C. Scanning electron microscope (SEM), X-ray diffraction (XRD) and thermogravimetric (TG) were used to characterize the pore shape, distribution and crystal phase change of the composite. The modified PP/SiO₂/PVDF composite film structure shows high strength and good thermal stability, and can better meet the requirements of strength and thermal performance of lithium-ion battery during the charging and discharging process.

Enhancement of the electrochemical performance of lithium-ion batteries by SiO2@poly(2-acrylamido-2-methylpropanesulfonic acid) nanosphere addition into a polypropylene membrane

Employing electrostatic self-assembly and free radical polymerization, the surface of SiO₂ nanospheres was coated with poly(2-acrylamido-2-methylpropanesulfonic acid) (SiO₂@PAMPS) bearing strong electron withdrawing sulfonic and amide groups, enhancing the dissociation ability of the lithium salt of the liquid electrolyte and absorbing anions via hydrogen bonds. After SiO₂@PAMPS nanospheres were introduced into the polypropylene (PP) membrane (SiO₂@PAMPS/PP), the electrolyte affinity and electrolyte uptake of the composite separators were significantly improved. The ionic conductivity of SiO₂@PAMPS/PP-18% (where 18% represents the concentration of the solution used for coating) soaked in liquid electrolyte was even 0.728 mS cm^-1 at 30 °C, much higher than that of the pristine PP membrane. The LiFePO₄/Li half-cell with SiO₂@PAMPS/PP-18% had a discharge capacity of 148.10 mA h g^-1 and retained 98.67% of the original capacity even after 120 cycles at 0.5C. Even at a rate of 1.0C, the cell capacity could be maintained above 120 mA h g^-1. Therefore, a coating formula was developed that could considerably improve the cycling ability and high rate charge-discharge performance of lithium ion batteries.