Jiaheng Lei

Advanced Separators for Lithium‐Ion and Lithium–Sulfur Batteries: A Review of Recent Progress

Li-ion and Li-S batteries find enormous applications in different fields, such as electric vehicles and portable electronics. A separator is an indispensable part of the battery design, which functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of the separators directly influence the performance of the batteries. Traditional polyolefin separators showed low thermal stability, poor wettability toward the electrolyte, and inadequate barrier properties to polysulfides. To improve the performance and durability of Li-ion and Li-S batteries, development of advanced separators is required. In this review, we summarize recent progress on the fabrication and application of novel separators, including the functionalized polyolefin separator, polymeric separator, and ceramic separator, for Li-ion and Li-S batteries. The characteristics, advantages, and limitations of these separators are discussed. A brief outlook for the future directions of the research in the separators is also provided.

Synthesis of ordered meso/macroporous H3PW12O40/SiO2 and its catalytic performance in oxidative desulfurization

Hierarchically ordered meso/macroporous phosphotungstic acid/SiO2 (HPW/SiO2) catalysts have been synthesized via the dual-templating method and used as a catalyst for oxidative desulfurization. The as-synthesized catalysts possess ordered macropores and well-ordered hexagonal mesopores within the walls of the macroporous cages. The HPW active species are finely dispersed in the silica matrix and retain its Keggin structure. Meso/macroporous HPW/SiO2 catalysts show superior catalytic performance with obvious improvement of the desulfurization rate compared to mesoporous HPW/SiO2 and macroporous HPW/SiO2. The high performance of the catalyst should be attributed to the structural characteristics of the meso/macropores. Furthermore, the catalyst was recovered and reused for seven runs with only a slight decrease in the catalytic performance.

Self-assembled meso/macroporous phosphotungstic acid/TiO2 as an efficient catalyst for oxidative desulfurization of fuels

Hierarchically meso/macroporous phosphotungstic acid/TiO2 (HPW/TiO2) have been successfully synthesized by evaporation induced self-assembly method with polystyrene microspheres and block copolymer P123 as templates. The as-synthesized meso/macroporous HPW/TiO2 catalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, nitrogen adsorption–desorption isotherms, Fourier transform infrared spectra and diffuse reflectance UV–Vis spectra. The results indicate that the catalysts possess disordered macropores and highly ordered mesopores, with Keggin type HPW embedded in the porous framework. The meso/macroporous catalysts exhibit excellent catalytic activity in oxidative desulfurization (ODS) of fuels. The catalytic performance of the meso/macroporous catalyst is markedly enhanced compared with that of pure mesoporous analogue under the same conditions. The high performance of the meso/macroporous catalyst should be attributed to the structural characteristics of meso/macopores, which improve the mass transfer and increase the accessible surface area of the catalyst. Moreover, the catalyst shows good recyclability, which makes it a promising catalyst in ODS process.

Effect of crosslink structure of bridge polycarboxylate superplasticizers on dispersion ability

Bridge polycarboxylate superplasticizers(PCs) with crosslink structure were synthesized by using polyethyleneglycol di-acrylate(PEGdA), replacing partial polyethyleneglycol mono-acrylate (PEGmA) as crosslinking agent. Structures of bridge PCs were analyzed by gel permeation chromatography, and dispersion ability was evaluated by cement paste dispersity variation on time and rheology test. The experimental results showed that, molecular weight(MW) of bridge PCs increased with increase of PEGdA proportion, and MW distribution curve changed from Gaussian to flat like, which meant notable increase of highly crosslinked copolymer. Bridge PCs led to decreased initial cement paste dispersity and better dispersity retention due to slow releasing. Further research showed that, PEGdA proportion had slight effect on polymerization degree of backbone, MW distribution of backbone deviated from Gaussian distribution and shoulder peaks appeared on distribution curve when PEGdA increased.

Synthesis and properties of methacrylate-based and allylether-based polycarboxylate superplasticizer in cementitious system

Methacrylate-based as well as allylether-based polycarboxylate superplasticizers (PCs) were prepared and evaluated in this paper. The architectures of PCs were characterized by Fourier transform infrared spectroscopy and Nuclear magnetic resonance as well as Gel permeation chromatography. For evaluation the performance of PCs, the adsorption behavior, zeta potential, and their relation to the fluidity of cement paste have been investigated, respectively. Additionally, retardation of PCs was tested by a heat calorimeter. The results showed that allyether-based PCs have a better slump retention ability, particularly their fluidity loss is smaller than that of the methacrylate-based PCs. Both types of PCs can delay the initial hydration of cement, which can be attributed to their different molecular structures and can be elucidated based on the results of the adsorption behavior and zeta potential of the cement particles. This investigation will provide useful information for choosing or designing the proper PCs to produce workable concrete.

Preparation of Polymethylacrylic Acid Standard Samples for GPC Applications via a Precipitation Fractionation-Separated Step Hydrolysis Method

A series of polymethylacrylic acid (PMAA) standard samples were prepared from fractionated PMMA samples followed by a two-step hydrolysis. The six PMMA standard samples with narrow molecular weight distributions were produced by free radical polymerization and fractionated with toluene-petroleum ether. Their average molecular weights ranged from 3.1 × 103 to 4.3 × 104, dispersion coefficients were less than 1.5, and their gel permeation chromatography (GPC) peak shapes were symmetrical. The PMMA standard samples were dissolved in dioxane, and then hydrolyzed in a saturated NaOH-methanol solution for 24 h, the methanol then evaporated, and after that the PMMA samples were hydrolyzed in a 2 mol ·L −1 NaOH aqueous solution for 24 h. The 1H-NMR results showed that the two-step hydrolysis degree was higher than 98.70%. The PMAA standard samples were obtained after acidifying the hydrolysates, namely polymethacrylic acid sodium salt, and their molecular weights were constant during the separation process. The acid–base titration results showed the purities of the PMAA samples were greater than 98.6%, and their molecular weight distributions were symmetrical and narrow. The molecular weights of the PMAA were determined by the stoichiometric relationship of the hydrolysis reaction. Compared with viscosimetry, the results of both methods were basically the same, and their errors were less than 10%.

Curing Characterization of the Bis-salicylaldehyde-triethylenetetramine Nickel (II)/Epoxy System

The curing reaction of epoxy resin and bis-salicylaldehyde-triethylenetetramine nickel (II) (Ni(sal)2trien) was investigated using differential scanning calorimetry (DSC), UV-vis spectrometer and FT-IR. DSC measurement showed two distinct exothermic peaks on the curing curves, indicating that the reaction consisted of two reactive species. The first peak at low temperature corresponded to the amine-epoxy reaction with the activation energy of 46.85 kJ · mol−1 and the second peak corresponded to the hydroxyl-epoxy reaction with the activation energy of 74.23 kJ · mol−1. As the concentration of Ni(sal)2trien increased, the amine–epoxy reaction was favored, and the temperature of the hydroxyl-epoxy reaction decreased at the same time.

Preparation of polycarboxylate-based superplasticizer and its effects on zeta potential and rheological property of cement paste

A series of polycarboxylate-based superplasticizers (PCs) with different structures were synthesized and the effects of chemical structure on zeta potential and rheological property of cement paste were studied. Residual monomers in each sample of PCs were quantitatively determined. The property of the polymers in cement was tested by micro-electrophoresis apparatus and R/S rheometer. Results showed that the zeta potential and its rheological properties are related with the side-chain length and density of PCs. The PCs having shorter side chain and lower side chain density exhibit higher anionic charge density, thus resulting in higher zeta potential. The effect of side chain density on zeta potential is more notable compared with that of side-chain length, and thus affecting the initial shear yield stress and apparent viscosity of the cement paste. In addition, although increasing the side chain length will result in reduction of the anionic charge density, the steric hindrance effect is obvious, which can effectively improve the dispersion of the cement particles, and reduce the viscosity and shear yield stress of slurry.

Three-dimensionally Ordered Macroporous Phosphotungstic Acid/SiO2 for Efficient Catalytic Oxidative Desulfurization

Three-dimensionally ordered (3DOM) macroporous phosphotungstic acid/SiO2 (HPW/SiO2) materials were prepared by using colloidal crystal as templates and applied for oxidative desulfurization (ODS) of the model fuel oil. The obtained HPW/SiO2 materials were characterized through scanning electron microscopy, powder X-ray diffraction, N2 sorption, and Fourier transform infrared spectroscopy. The results indicated that 3DOM HPW/SiO2 possessed hierarchical pore architectures which contained ordered macropores and disordered mesopores, with the Keggin type HPW embedded in the framework of pore structure. The removal rate of dibenzothiophene (DBT) could reach 100% under the optimum conditions, moreover. The performance was only slightly decreased for the regenerated catalyst after 7 cycles.

Synthesis of a novel polycarboxylate superplasticizer with carboxyl group as side chain terminal group to enhance its clay tolerance

The dispersion ability of polycarboxylate superplasticizer (PCE) in fresh concrete was much impeded by clay impurities. To improve the dispersion of PCE in the clay-contained concrete, a novel PCE with carboxyl as a specific branched chain terminal group was synthesized, using modified polyether as the raw material which was prepared through esterification between hexahydrophthalic anhydride (HHPA) and isobutenyl polyoxyethylene ether (IPEG) with hydroxy as the terminal group. The esterification product and PCE molecular structure were characterized by infrared spectroscopy and 1HNMR resonance. The results confirmed that the product molecular structure was a comb-type copolymer with long-chain terminal carboxyl group and PEO attached directly to the backbone chain. The as-synthesized PCEs had favorable dispersibility in cement than conventional PCE in the presence of montmorillonite (Mmt) clay. This can be attributed to the introduction of electronegative carboxyl to PCE long-chain terminal group, which reduces the adsorption of PCE on Mmt, and thus improves the tolerance of PCE to the Mmt.