Covalent Organic Framework-Coated Polyimide Ion-Track-Etched Separator with High Thermal Stability for Developing Lithium-Ion Batteries with Long Lifespans.

Separators play a crucial role in inhibiting thermal runaway in lithium-ion batteries (LIBs). In this study, the doctor blade coating method and heavy-ion track etching technology were used to prepare a polyimide-based covalent organic framework (PI_COF) separator with excellent thermal stability and a long cycle life. Specifically, COF300 was simply coated on the surface of a polyimide-based track-etched membrane (PI_TEM) with straight through holes, which provided a rigid framework and high-temperature stability at 300 °C. These features were conducive to inhibiting thermal runaway, while porous COF300 with large holes increased the wettability of the electrolyte, facilitating lithium-ion migration and suppression of lithium dendrite growth; consequently, LIBs with an excellent cycling performance and a high rate capacity were obtained. The cell with the PI_COF separator delivered a high capacity of 90.0 mA h g-1 after 1000 cycles. The PI_COF separator with high thermal stability exhibited a long cycle life in LIBs. These features are beneficial for improving the safety characteristics of LIBs as well as for accelerating the practical application process of the PI_COF separator.

Schottky barrier reduction on optoelectronic responses in heavy ion irradiated WSe2 memtransistors.

Two-dimensional transition metal dichalcogenide-based memtransistors provide simulation, sensing, and storage capabilities for applications in a remotely operated aerospace environment. Swift heavy ion (SHI) irradiation technology is a common method to simulate the influences of radiation ions on electronic devices in space environments. Here, SHI irradiation technology under different conditions was utilized to produce complex defects in WSe2-based memtransistors. Low-resistance state to low-resistance state (LRS-LRS) switching behaviors under light illumination were achieved and photocurrent responses with different spike trains were observed in SHI-irradiated memtransistors, which facilitated the design of devices with enriched analog functions. Reduction of the Schottky barrier height due to the introduced defects at the metal/WSe2 interface was confirmed to be the major factor responsible for the observed behaviors. 1T phase and concentric circle-type vacancies were also created in the SHI-irradiated 2H-WSe2 channel besides the amorphous structure; these complex defects could seriously affect the transport properties of the devices. We believe that this work serves as a foundation for aerospace radiation applications of all-in-one devices. It also opens a new application field of heavy ion irradiation technology for the development of multiterminal memtransistor-based optoelectronic artificial synapses for neuromorphic computing.

Sheet-Like Stacking SnS2/rGO Heterostructures as Ultrastable Anodes for Lithium-Ion Batteries.

SnS2-based materials have attracted considerable attention in energy storage and conversion owing to their high lithium activity and theoretical capacity. However, the practical application is severely limited by the low coulombic efficiency and short cycle life due to irreversible side reactions, low conductivity, and serious pulverization in the discharge/charge process. In this study, sheet-like stacking SnS2/reduced graphene oxide (rGO) heterostructures were developed using a facile solvothermal method. It was found that the composites between SnS2 nanoplates and rGO nanosheets are closely coupled through van der Waals interactions, providing efficient electron/ion paths to ensure high electrical conductivity and sufficient buffer space to alleviate volume expansion. Therefore, the SnS2/rGO heterostructure anode can obtain a high capacity of 840 mA h g-1 after 120 cycles at a current density of 200 mA g-1 and maintain a capacity of 450 mA h g-1 after 1000 cycles at 1000 mA g-1. In situ X-ray diffraction tests showed that SnS2/rGO undergoes typical initial intercalation, conversion, and subsequent alloying reactions during the first discharge, and most of the reactions are dealloying/alloying in the subsequent cycles. The galvanostatic intermittent titration technique showed that the diffusion of lithium ions in the SnS2/rGO heterostructures is faster in the intercalation and conversion reactions than in the alloying reactions. These observations help to clarify the reaction mechanism and ion diffusion behavior in the SnS2 anode materials, thus providing valuable insights for improving the energy efficiency of lithium-ion batteries.

Sandwich-like SnS2/graphene multilayers for efficient lithium/sodium storage.

2D materials have attracted extensive attention in energy storage and conversion due to their excellent electrochemical performances. Herein, we report utilization of monolayer SnS2 sheets within SnS2/graphene multilayers for efficient lithium and sodium storage. SnS2/graphene multilayers are synthesized through a solution-phase direct assembly method by electrostatic interaction between monolayer SnS2 and PDDA (polydimethyl diallyl ammonium chloride)-graphene nanosheets. It has been shown that the SnS2/graphene multilayer electrode has a large pseudocapacity contribution for enhanced lithium and sodium storage. Typical batteries deliver a stable reversible capacity of ∼160 mA h g-1 at 2 A g-1 after 2000 cycles for lithium and a stable reversible capacity of ∼142 mA h g-1 at 1 A g-1 after 1000 cycles for sodium. The excellent electrochemical performances of SnS2/graphene multilayers are attributed to the synergistic effect between the monolayer SnS2 sheets and the PDDA-graphene nanosheets. The multilayer structure assembled by different monolayer nanosheets is promising for the further development of 2D materials for energy storage and conversion.

Performance comparison of chiral separation materials derived from N-cyclohexylcarbonyl and N-hexanoyl chitosans.

Chitosan bis(phenylcarbamate)-(N-cyclohexylformamide)s and chitosan bis(phenylcarbamate)-(N-hexanamide)s were synthesized as chiral selectors for enantiomeric separation. Since two types of substituents with different structures were, respectively, introduced onto the 2-position and the 3-/6-positions of the glucose skeleton in the chitosans through a "heterogeneous" modification pathway, the enantioseparation performances of the chiral selectors could be improved. Influence of the type and position of the substituents on chiral recognition and enantioseparation abilities was studied in detail, and the structural dependence on enantioseparation performance was particularly demonstrated. It was found that methyl- and chloro-substituted chitosan bis(phenylcarbamate)-(N-hexanamide)s possessed comparable enantioseparation performances, whereas chloro-substituted chitosan bis(phenylcarbamate)-(N-cyclohexylformamide)s exhibited much more powerful chiral recognition and enantioseparation abilities than the methyl-substituted ones. Among all the prepared chiral selectors, those with the combination of the cyclohexyl group at the 2-position of the glucose skeleton in the chitosan derivatives and the chlorophenyl group at the 3-/6-positions seemed to be more preferable for enantiomeric separation. As a result, the chitosan bis(3,4-dichlorophenylcarbamate)-(N-cyclohexylformamide) possessed the best enantioseparation performance. The solvent tolerability of the prepared chiral selectors was also investigated in the present study. Compared with the classical coated-type chiral separation materials derived from cellulose/amylose derivatives, the N-cyclohexylcarbonyl and N-hexanoyl chitosans based chiral stationary phases were observed to possess more favorable solvent tolerability, thus possibly widening their applications for various practical enantioseparations.

Large Rectification Effect of Single Graphene Nanopore Supported by PET Membrane.

Graphene is an ideal candidate for the development of solid state nanopores due to its thickness at the atomic scale and its high chemical and mechanical stabilities. A facile method was adopted to prepare single graphene nanopore supported by PET membrane (G/PET nanopore) within the three steps assisted by the swift heavy ion irradiation and asymmetric etching technology. The inversion of the ion rectification effect was confirmed in G/PET nanopore while comparing with bare PET nanopore in KCl electrolyte solution. By modifying the wall charge state of PET conical nanopore with hydrochloric acid from negative to positive, the ion rectification effect of G/PET nanopore was found to be greatly enhanced and the large rectification ratio up to 190 was obtained during this work. Moreover, the high ionic flux and high ion separation efficiency was also observed in the G/PET nanopore system. By comparing the "on" and "off" state conductance of G/PET nanopore while immersed in the solution with pH value lower than the isoelectric point of the etched PET (IEP, pH = 3.8), the voltage dependence of the off conductance was established and it was confirmed that the large rectification effect was strongly dependent on the particularly low off conductance at higher applied voltage.

N-Acylated chitosan bis(arylcarbamate)s: A class of promising chiral separation materials with powerful enantioseparation capability and high eluents tolerability.

In order to comprehensively understand the influence of coordination of the substituent at 2-position with those at 3- and 6-positions on the properties of chitosan derivatives, a series of chitosan 3,6-bis(arylcarbamate)-2-(amide)s (CACAs) and the related chiral stationary phases (CSPs) were prepared and reported in the present study. Specifically, chitosan was N-acylated with carboxylic acid anhydrides, and then further derivatized with various aryl isocyanates to afford CACAs, from which a class of coated-type CSPs were prepared. When the substituent introduced on the acyl group at 2-position and those on the phenyl group of the carbamates at 3- and 6-positions were fittingly combined, these prepared CACAs based CSPs would exhibit powerful chiral recognition ability, further resulting in a class of promising chiral separation materials with excellent enantioseparation performance. Meanwhile, these newly developed materials with suitable molecular weight also bear a high tolerability towards organic solvents, even including pure tetrahydrofuran, thus broadening their application in enantiomeric separation.

Enantioseparation characteristics of biselector chiral stationary phases based on derivatives of cellulose and amylose.

Cellulose tris(4-methylphenylcarbamate) (CMPC) and cellulose tris(4-chlorophenylcarbamate) (CCPC) are well known for their powerful chiral recognition capability, and the chiral columns prepared from these two polymers have been commercialized. However, the chiral stationary phases (CSPs) can be only used in the mobile phases containing no more than 20% ethanol (referring to CMPC) or cannot be used in ethanol-containing mobile phases (referring to CCPC). In order to overcome the defect and to study the enantioseparation characteristics of biselector CSPs, CMPC, cellulose tris(phenylcarbamate) (CPC) and CCPC were, respectively, mixed with amylose tris(3,5-dimethylphenylcarbamte) (ADMPC) at a ratio of 1:1 (mol/mol) of glucose unit, and three new CSPs were prepared by coating the resulting blends on 3-aminopropyl silica gel. For the purpose of enantioseparation comparison, the corresponding single selector CSPs were also prepared with the individual derivatives of cellulose and amylose. The enantioseparation evaluation indicated that the biselector CSPs still bear excellent enantioseparation capability. The interaction between two polymers in each blend was investigated by using circular dichroism (CD) spectroscopy. Owing to the interaction, the durability of the biselector CSP derived from CMPC and ADMPC was significantly improved. The CSP could be analyzed with a mobile phase of 100% ethanol. And the biselector CSP derived from CCPC and ADMPC could safely work in a normal phase containing 30% ethanol. Therefore, the workable ranges of the mobile phases were broadened. The elution order on the biselector CSPs was generally dominated by the one on the corresponding single selector CSPs that provided a higher resolution. In addition, the suprastructure variation caused by the interaction between the individual polymers might also affect the enantioseparation of the biselector CSPs. The trends of the retention factors and the resolutions of partially racemic mixtures were discussed.