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[en] This paper presents a systematic study of the dose response characteristics of two new models and one commonly used model of GAFCHROMIC film: HS, XR-T, and MD55-2, respectively. We irradiated these film models with three different radiation sources: I-125, Ir-192, and 6 MV photon beam (6 MVX). We scanned the films with three different densitometers: a He-Ne laser with a wavelength of 633 nm, a spot densitometer with a wavelength of 671 nm, and a CCD camera densitometer with interchangeable LED boxes with wavelengths of 665 nm (red), 520 nm (green), and 465 nm (blue). We compared the film sensitivities in terms of net optical density (NOD) per unit dose in Gy. The sensitivity of each film model depends on radiation energy and the densitometer light source. Using He-Ne laser based densitometer as a reference standard, we found the sensitivities (NOD/Gy) for the red lights of wavelengths, 671 nm and 665 nm, are higher by factors of about 2.5 and 2, respectively. The sensitivities for green (520 nm) and blue (465 nm) lights are lower than that for He-Ne laser (633 nm) by factors of about 2 and 4, respectively. The energy dependence of the sensitivity varies with the film model, but is similar for all densitometer light sources. Comparing I-125 to Ir-192 and 6MVX, we note that (a) model XR-T is about eight times more sensitive, and (b) models HS and MD55-2 are about 40% less sensitive. Relative to MD55-2, XR-T is 12 times more sensitive for I-125 but comparable for Ir-192 and 6MVX, whereas HS is 2 to 3 times more sensitive in all cases. This set of results can serve as useful information for making decisions in selecting the film model and compatible densitometer to achieve the best accuracy of dosimetry in the appropriate dose range
[en] Highlights: • Large quantities of high quality, two-dimensional (2D) vanadium pentoxide (V2O5) nanosheet (NS) have been exfoliated in environmental friendly solvents. • Large-area, flexible and binder-free V2O5 NS/SWCNT hybrid electrodes have been efficiently fabricated through programmed aerosol printing technique. • The interlayer spacing of 2D orthorhombic V2O5 NS can be well manipulated, ranging from 4.4Å to 11.5 Å in ethanol and water-based colloidal solutions, respectively. • The SWCNT further improves the reversible phase transition reactions of the V2O5 NS and maintains the structural integrity of the electrodes. • The flexible printed V2O5 NS/SWCNT electrode has demonstrated a high discharge capacity of 370 mA h g−1 at 0.05 C, high energy density (1110 W h kg−1) and power density (4350 W kg−1), etc. With a layered crystal structure and good Li+ storage performance, vanadium pentoxide (V2O5) is potentially a high-energy and cost-effective cathode material for Li-ion batteries (LiBs). Networks of two-dimensional V2O5 nanosheets (2D V2O5 NS), with large interlayer distance, are ideal for enhancing the Li+ diffusion kinetics and thus for building high power LiBs. However, the lack of a simple, scalable and environmentally friendly route to nanosheet production still hinders the development of V2O5 applications. Here we demonstrate, liquid-phase exfoliation (LPE) of commercial V2O5 powder in environmental friendly solvents (water and ethanol) to achieve large quantities of 2D V2O5 NS dispersions. The V2O5 NS are of high-quality whose interlayer spacing can be well manipulated, ranging from 4.4Å to 11.5 Å in ethanol and water (forming NS xerogel), respectively. Ultrasonic aerosol printing of V2O5 NS xerogel/single-wall carbon nanotube (SWCNT) blended dispersions resulted in large-area, flexible, and binder-free hybrid electrodes, which showcase a high discharge capacity of 370 mA h g−1 at 0.05 C, high energy density (555 W h kg−1) and power density (2175 W kg−1), etc. These properties can be attributed to the synergistic effects between the expanded hydrated NS and the conductive SWCNT matrix; the latter improves the reversible phase transition reactions of the NS, enhances the ion diffusion kinetics, maintains the electrode's mechanical integrity and provides electron transport pathways. The Li+ storage mechanism was investigated, suggesting the capacity was majorly contributed by the non-diffusion controlled process (pseudocapacitive). We believe the LPE/aerosol printing approach is environmentally green, general and scalable, and could be extended to other layered transitional metal oxides or dichalcogenides for fabrication of corresponding flexible, binder-free, conductive composites for energy storage systems.
[en] Graphical abstract: Mesoporous carbon microspheres (MCMs) with tunable pore sizes have been prepared via a high-throughput spray drying-assisted hard template method and used as the hosts to load selenium (Se) for Li-Se batteries. - Abstract: Mesoporous carbon microspheres (MCMs) with tunable pore sizes have been prepared via a high-throughput spray drying-assisted hard template method and used as the hosts to load selenium (Se) for lithium-selenium (Li-Se) batteries. The pore size control of the MCMs (3.8, 5, 6.5, 9.5 nm) was achieved by in-situ polymerized colloid silica templates with different sizes, thus prompting us to focus on tracing the effects of mesopore size on electrochemical performance of MCMs/Se cathodes. The results reveal that relative higher capacity and better cycling performance are presented in MCMs with smaller pores size due to the more effective confinement effect. At an optimal pore size of 3.8 nm, the MCMs/Se with 50% Se loading delivers an initial capacity of 513 mAh g"−"1 and capacity retention of 300 mAh g"−"1 after 100 cycles at 0.5 C. Furthermore, it is concluded that nitrogen doping could assist MCMs to retard the diffusion of polyselenide species possibly via an enhanced surface adsorption. The composites thus increase the reversible capacity by 30% after 100 cycles compared with the nitrogen-free composite. These results indicate that controlling pore structure and surface chemistry are good strategies to optimize the electrochemical performance of C/Se based cathodes for Li–Se batteries
[en] Guiding the lithium ion (Li-ion) transport for homogeneous, dispersive distribution is crucial for dendrite-free Li anodes with high current density and long-term cyclability, but remains challenging for the unavailable well-designed nanostructures. Herein, we propose a two-dimensional (2D) heterostructure composed of defective graphene oxide (GO) clipped on mesoporous polypyrrole (mPPy) as a dual-functional Li-ion redistributor to regulate the stepwise Li-ion distribution and Li deposition for extremely stable, dendrite-free Li anodes. Owing to the synergy between the Li-ion transport nanochannels of mPPy and the Li-ion nanosieves of defective GO, the 2D mPPy-GO heterostructure achieves ultralong cycling stability (1000 cycles), even tests at 0 and 50 °C, and an ultralow overpotential of 70 mV at a high current density of 10.0 mA cm, outperforming most reported Li anodes. Furthermore, mPPy-GO-Li/LiCoO full batteries demonstrate remarkably enhanced performance with a capacity retention of >90 % after 450 cycles. Therefore, this work opens many opportunities for creating 2D heterostructures for high-energy-density Li metal batteries. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] Highlights: • Colloidal Ti_3CNTx MXene was prepared in the absence of HF or organics intercalation. • The restacking of delaminated Ti_3CNT_x flakes was greatly suppressed by freeze-drying. • The freeze-dried Ti_3CNT_x shows developed ion diffusion paths with abundant voids. • The capacity of freeze-dried Ti_3CNT_x reaches 300 mAh/g at 0.5 A/g after 1000 cycles. • The delamination/freeze-drying process for MXene is facile, scalable, and general. - Abstract: Developing powerful Li-ion batteries require advanced nanostructured electrodes. Transition metal carbides or nitrides, known as MXenes, are an emerging family of two-dimensional materials. However, the lacking of an environmental-friendly preparation of colloidal MXene with few nanosheets-restacking greatly limits their usage in batteries and compromises the electrochemical performances. Here, we obtained the aqueous titanium carbonitride (Ti_3CNT_x) colloidal solution in the absence of hydrofluoric acid or organic solvents’ intercalation processes. We further suppressed the notorious nanosheets restacking issue through a freeze-drying strategy of the colloidal dispersion. The resulted Ti_3CNT_x powder, with a “fluffy” morphology and quite few percentage of restacked nanosheets, displays good charge storage capacities, high rate handling and excellent cycling performance, for example, a discharge capacity of 300 mAh g"−"1 at 0.5 A g"−"1 after 1000 cycles has been achieved.
[en] Highlights: • Highly transparent ruthenium oxide/poly(3,4-ethylenedioxythiophene): poly(styrene-4-sulfonate), (RuO2/PEDOT:PSS) hybrid thin films have been successfully fabricated. • The hybrid thin film shows remarkably high transparency (93%), high conductivity (σDC =279 S/cm), excellent volumetric capacitance (CV =190 F/cm3) and areal capacitance of C/A=1.2 mF/cm2. • Transparent, flexible devices have been fabricated with excellent electrochemical performances, such as C/A=0.84 mF/cm2 and 100% capacitance retention over 10,000 charge/discharge cycles. • Large-area transparent supercapacitor device has been built. Transparent, conductive electrodes are important in many applications such as touch screens, displays and solar cells. Transparent energy storage systems will require materials that can simultaneously act as current collectors and active storage media. This is challenging as it means improving the energy storage capability of conducting materials while retaining transparency. Here, we have used aerosol-jet spraying strategy to prepare transparent supercapacitor electrodes from ruthenium oxide/poly(3,4-ethylenedioxythiophene): poly(styrene-4-sulfonate), (RuO2/PEDOT: PSS) hybrid thin films. These films combine excellent transparency with reasonably high conductivity (DC conductivity =279 S/cm) and excellent volumetric capacitance (CV =190 F/cm3). We demonstrate electrodes with historical high transparency of 93% which display an areal capacitance of =1.2 mF/cm2, significantly higher than the rest reported electrodes with comparable transparency. We have assembled flexible, transparent, solid-state symmetric devices which exhibit T=80% and =0.84 mF/cm2 and are stable over 10,000 charge/discharge cycles. Asymmetric solid-state device with RuO2/PEDOT: PSS and PEDOT: PSS thin films as positive and negative electrodes, respectively, display an areal capacitances of 1.06 mF/cm2, a maximum power density of 147 μW/cm2 and an energy density of 0.053 μWh/cm2. Furthermore, large area transparent solid-state supercapacitor device has been built. We believe the solution-processed transparent films could be easily scaled-up to meet the industrial demands.
[en] Though anodes with high Li gravimetric capacities, beyond commercial graphite, have been intensively studied, gravimetric capacity does not precisely reflect the performance of a packed cell. Li anodes with high mass loadings, which can achieve high areal capacities, are required for many commercial applications. Herein, anodes with high mass loadings were fabricated using two-dimensional transition metal carbides (MXenes). Powders of the latter were cold pressed, without binders, at a pressure of 1 GPa, to create ∼300 μm thick, free-standing discs. When Ti_3C_2 was used as the anode for lithium, the initial reversible areal capacity was ∼15 mAh/cm"2, which decreased to 5.9 mAh/cm"2 after 50 cycles, but the decrease after the first ∼20 cycles was very gradual. The latter is one of the highest values ever reported to date. When Nb_2C was used as the anode instead, the initial reversible capacity was ∼16 mAh/cm"2; this value decreased to 6.7 mAh/cm"2 after 50 cycles, which is about a 14% increase compared to Ti_3C_2. As the research on MXenes for lithium ion batteries has just begun, there is certainly room for further improving their electrochemical performance