High Thermal Shrinkage Research Articles

Thermostable and nonflammable polyimide/zirconia compound separator for lithium-ion batteries with superior electrochemical and safe properties

Separators are applied to segregate cathode and anode, and provide ion transport channels in lithium-ion batteries (LIBs). Nevertheless, present commercial polyolefin separators represent high thermal shrinkage and inferior electrolyte wettability, seriously limiting wider development of LIBs. In this work, we prepared zirconia (ZrO2) nanolayer encapsulated polyimide (PI) nanofiber compound separator through in-situ polar adsorption and hydrolysis strategy. The obtained PI/ZrO2 compound separator has superior thermal stability, electrolyte wettability and flame retardance in comparison with polypropylene (PP) separator. The shrinkage ratio of prepared PI/ZrO2 compound separator is 0 even at 300 °C, while the PP separator significantly shrank at 160 °C. Furthermore, the ionic conductivity of PI/ZrO2 separator reaches up to 1.32 mS cm−1, far higher than 0.34 mS cm−1 of PP separator. Besides, the coin batteries of LiNi0.8Co0.1Mn0.1O2 (NCM811)/electrolyte-separator/lithium (Li) assembled with PI/ZrO2 compound separator exhibit enhanced rate performance, high discharge capacity retention rate of 88.3% after 100 cycles at 1C and excellent battery safety performance even at 140 °C. Thus, combined with its advantages, such as preparation, thermostability, electrolyte wettability, electrochemical property and safety, the PI/ZrO2 compound separator exhibits promising prospect in the application of commercial LIBs.

High-performance polyethylene separators for lithium-ion batteries modified by phenolic resin

In lithium-ion batteries, separator serves to isolate the positive and negative electrodes, as well as provide a free shuttle for Li-ion transport inside the battery. Commercial polyolefin separator has relatively higher thermal shrinkage and lower electrolyte wettability, which limits the application of batteries in extreme conditions. In this work, we prepared phenolic resin (AF) modified polyethylene (PE) composite separators by the process of immersion in situ reaction. The obtained PE@AF composite separator has lower thermal shrinkage and higher electrolyte wettability than pure PE separator. The shrinkage of our prepared PE@AF separator is only 6% when stored at 145 °C for 30 min, greatly smaller than the pure PE separator (more than 77%). Moreover, the ion conductivity of PE@AF composite separator increases from 0.206 mS cm−1 for the pure one to 0.604 mS cm−1. Apart from this, the Li/electrolyte-soaked PE@AF separator/LiFePO4 battery exhibits a higher coulombic efficiency (96.7%) and discharge capacity retention rate (86.0%) after 450 cycles than the pure one (67.4% and 72.7%, respectively). Our results indicate that the AF coating plays a vital part in improving the thermal stability and electrochemical property of polyolefin separators.

Self-assembled nano-silica-embedded polyethylene separator with outstanding physicochemical and thermal properties for advanced sodium ion batteries

Sodium ion batteries (NIBs) provide significant advantages for large-scale energy conversion and storage devices. NIBs are extensively investigated because of the global abundance of Na resources. The Na ion is similar to the Li ion; however, the conventional poly(ethylene) (PE) separator used in Li ion batteries is unsuitable for NIBs because of its extremely poor wettability by the Na+ electrolyte and its high thermal shrinkage. These properties can cause severe safety issues at elevated temperatures, as well as poor ionic conductivities. Therefore, the PE separator needs modification for use in high-performance NIBs. Here, we propose a unique nano-SiO2 impregnation method that preserves the thickness of the separator to ensure a high volumetric energy density. Silica matrices are incorporated into the PE separator through a simple chemical modification that includes embedding the hydroxyl group by benzoyl peroxide treatment, followed by Si–O condensation to introduce 3-(trimethyloxysilyl)propyl methacrylate auxiliaries. These steps allow the introduction of multiple Si–O functional groups onto the PE backbone through chemical reactions with tetraorthosilicate. The proposed separator exhibits high wettability and ionic conductivity while maintaining the initial separator thickness. The nano-SiO2-impregnated PE has significantly improved thermal stability and high dimensional stability even at an elevated temperature of 140℃. Na full-cell systems, consisting of Na0.9Li0.05Ni0.25Fe0.25Mn0.5O2 and hard carbon electrodes, exhibit considerably increased cycle lives and rate capabilities when fabricated with this nano-SiO2-impregnated PE separator.

Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature

Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for geopolymers has been reported in literature at a microscale. However, their performance at macroscale has not yet been systematically explored and the underlying mechanisms remain unexplained. In current study, effect of variation in Si/Al molar ratio on the meso- and macro-scale thermal stability of metakaolin geopolymers has been comprehensively investigated to discover the underlying mechanisms governing the performance. Results show that all the geopolymer samples experienced reduction in compressive strengths after exposure to high temperature up to 900°C. Although, the geopolymer mixes exhibited good chemical stability at microscale, they possessed poor volume stability at mesoscale with very high thermal shrinkage. It was observed that thermal shrinkage induced crack formation dominates the residual strength for geopolymer mixes with Si/Al molar ratio ≤ 1.50, while densification of matrix is the governing factor of the residual strength for geopolymer mixes with Si/Al molar ratio > 1.50. Re-crystallization of nepheline at high temperature adversely affect the strength by inducing expansion and cracking of the geopolymer matrix. Geopolymer sample with Si/Al ratio 1.75 retained highest strength (6MPa) because viscous sintering of geopolymer mixes with high Si/Al ratio at temperature beyond 600°C enables localized healing of micro-cracks and densification of matrix which favored compressive strength gain after exposure to 900°C. At an even higher Si/Al of 2.0, foaming of unreacted silica upon heating can lead to expansion and cracking of the sample which reduce the strength. It was observed that due to high degree of cracking damage and low residual strength retention, it is essential to improve the macro-scale stability of metakaolin geopolymers for structural fire resistance applications.

Toward High-Performance Poly(l-lactide) Fibers via Tailoring Crystallization with the Aid of Fibrillar Nucleating Agent

As a sustainable alternative to conventional petrochemical-based polymers, biobased and biodegradable poly(l-lactide) (PLLA) exhibits tremendous application potential in the textile industry due to its attractive elastic recovery, moisture regain, and flammability. However, the commercial adoption of PLLA textile fibers still faces some hurdles mainly associated with their poor heat resistance (i.e., high thermal shrinkage or low dimensional stability) because the low crystallization rate makes PLLA difficult to crystallize during melt spinning. Herein, we report a simple but robust strategy to address this hurdle via simultaneously manipulating crystallinity and lamellae orientation with the aid of a highly active nucleating agent (NA) that can be completely dissolved in PLLA melt and reorganize into fine fibrils upon cooling. By taking full advantage of strong elongational flow field involved in the melt spinning, the NA fibrils with high nucleation efficiency on PLLA crystallization tend to align along...

Polyethylene terephthalate/poly (vinylidene fluoride) composite separator for Li-ion battery

Electrospun nanofiber membranes have been proved to enhance performances of Li-ion batteries, but their poor mechanical strength hinders their industrial application. This paper combines meltblown polyethylene terephthalate (PET) nonwoven and electrospun poly (vinylidene fluoride) (PVDF) membrane together to improve the mechanical property via hot-pressing, wherein a dried 3 wt% PVDF solution coating on PET nonwoven is used as a binder. The hot-pressing temperature is optimized to be 145 °C and the composite PET/PVDF separator exhibits an excellent mechanical property, whose transverse and longitudinal tensile strength could reach 13.70 and 34.85 MPa respectively. Compared with a commercial PP separator, the hot-pressed PET/PVDF membrane separator shows better wettability, higher thermal shrinkage and improved electrochemical performance as well.

Polyethylene terephthalate/poly(vinylidene fluoride) composite separator for Li-ion battery

Electrospun nanofiber membranes have been proved to enhance the performance of a Li-ion battery (LIB), but their poor mechanical strength hinders their industrial application. This paper combines a meltblown polyethylene terephthalate (PET) nonwoven and a electrospun poly(vinylidene fluoride) (PVDF) membrane together to improve the mechanical property via hot-pressing, wherein a dried 3 wt% PVDF solution coating on PET nonwoven is used as a binder. The experiment results indicate that the hot-pressing PET/PVDF separator exhibits an excellent mechanical property, whose transverse and longitudinal tensile strength could reach 13.70 MPa and 34.85 MPa respectively. Compared with a commercial PP separator, the hot-pressing PET/PVDF membrane separator shows better wettability, higher thermal shrinkage and excellent discharge capacity as well.

Mechanical Analysis for ITER Lower CC Feeder

ITER correction coils (CCs) feeder is the important component of ITER feeder systems to supply the cryogens and electrical power for CCs. They should withstand the huge electromagnetic (EM) force and high thermal shrinkage. Considering the EM and thermal loads, mechanical analysis is performed to qualify the structural strength of the lower CC feeder. Results show that containment duct and cryopipe can meet the static criteria but busbar jacket cannot meet. It is proposed that more supports should be added at the corners for the busbar. Basically, the lower CC feeder design is valid and feasible.

Residual strength properties of sodium silicate alkali activated slag paste exposed to elevated temperatures

The residual compressive strength behavior of alkali activated slag paste (AASP) after temperature exposures up to 1,200°C was investigated. Strength loss of approximately 60% occurred between 100 and 200°C and a further strength loss in the order of 30% at 800°C. Total loss of strength occurred at 1,200°C. Thermogravimetric studies (TGA/DTG) verified AASP contained no Ca(OH)2 which governs the chemical mechanism of strength loss for ordinary Portland cement (OPC) and blended slag cement pastes. However, the TGA results showed that AASP had a higher water loss than the other binders between 100 and 200°C and higher thermal shrinkage as indicated by the dilatometry studies. The high thermal shrinkage led to a differential thermal shrinkage gradient within the AASP and induced micro stresses and cracking which was more prominent for larger samples. Differential thermal shrinkage caused by the higher thermal shrinkage of the AAS material was concluded as the mechanism which gives lower residual strength in AASP compared to OPCP.

Thermal stability of connective tissue from porcine muscles

Connective tissue of three porcine muscles ( M. infraspinatus, IS; M. longissimus dorsi, LD; M. semimembranosus, SM) from 27 animals [populations A ( n = 13, reared in Ireland) and B ( n = 14, reared in Finland)] was studied by measuring the collagen content, collagen solubility and thermal shrinkage temperature of the connective tissue. Colour and pH were also determined. Collagen solubility was highest in IS ( p < 0.05) and lowest in SM ( p < 0.05) although no difference between LD and SM was found in population B. The onset and peak temperatures of thermal shrinkage ( T o and T p) were highest in IS ( p < 0.05). The lowest T o and T p were found in SM from population B whereas no differences were seen between LD and SM muscles in population A. It was concluded that the thermal stability of the connective tissue in the three porcine muscles differ. IS, as a dark muscle has high thermal shrinkage temperatures and high collagen solubilities in comparison to the lighter LD and SM muscles which have lower thermal shrinkage temperatures and collagen solubilities. Collagen contents were highest in IS and lowest in LD.

Physical and chemical modification of polyester fibres and filaments to improve the consumer properties of the finished articles

Different types of polyester fibres and filaments with valuable consumer properties are obtained by physical modification of PET. The fibres from chemically modified PET have high dyeability with disperse and cationic dyes, high thermal shrinkage, and low pilling in comparison to standard polyester. A polyester fibre with low combustibility (OI > 27) was made by incorporating fireproofing compounds in polycondensation of PET.

Characteristics of residual stress generated by MoSi2 plasma thermal spraying

Summary This paper describes an investigation of plasma thermal spraying of MoSi2 offering a high melting point together with excellent high-temperature oxidation resistance. MoSi2 powder was deposited by low-pressure plasma thermal spraying on the surfaces of blasted SS400 substrate specimens precoated with 50%Ni-50%Cr. The residual stress generated in the specimens was then determined. Compressive stress is generated in the MoSi2 sprayed deposit. Tensile stress is generated in the 50%Ni-50%Cr sprayed deposit except at the SS400 substrate surface. A series of experiments was conducted to clarify the validity of the residual stress distribution obtained. These results suggest the following: 1. When only blasting treatment is performed, compressive stress is generated from the upper surface to 0.3 mm inside. Minor tensile stress is also generated inside. 2. When 50%Ni-50%Cr is deposited after blasting treatment, the residual stress is tensile in the 50%Ni-50%Cr layer and compressive on the substrate upper surface. Tensile stress is found inside. This is due to the fact that the substrate restrains the contraction of the sprayed deposit with a high thermal shrinkage. The validity of this result is also supported by the fact that the compressive stress near the substrate upper surface is greater than when only blasting treatment is performed. 3. When MoSi2 is deposited after blasting treatment, compressive stress is generated in the MoSi2 layer. This is due to the fact that, despite the MoSi2 layer having a higher temperature than the substrate, the linear thermal expansion coefficient of MoSi2 is much smaller than that of the substrate, so that the MoSi2 layer restrains the contraction of the substrate. 4. During estimation of the residual stress in materials deposited by plasma thermal spraying, it is important to ensure that the modulus of elasticity of the sprayed deposit is measured separately for each set of thermal spraying conditions.