Visualization of Sodium Metal Anodes via Operando X-Ray and Optical Microscopy: Controlling the Morphological Evolution of Sodium Metal Plating

Because of the abundance and cost effectiveness of sodium, rechargeable sodium metal batteries have been widely studied to replace current lithium-ion batteries. However, there are some critical unresolved issues including the high reactivity of sodium, an unstable solid-electrolyte interphase (SEI), and sodium dendrite formation. While several studies have been conducted to understand sodium plating/stripping processes, only a very limited number of studies have been carried out under operando conditions. We have employed operando X-ray and optical imaging techniques to understand the mechanistic behavior of Na metal plating. The morphology of sodium metal plated on a copper electrode depends strongly on the salts and solvents used in the electrolyte. The addition of a fluorine-containing additive to a carbonate-based electrolyte, NaClO₄ in propylene carbonate (PC):fluoroethylene carbonate (FEC), results in uniform sodium plating processes and much more stable cycling performance, compared to NaClO₄ in PC, because of the formation of a stable SEI containing NaF. A NaF layer, on top of the sodium metal, leads to a much more uniform deposition of sodium and greatly enhanced cyclability.

Understanding the Impacts of Li Stripping Overpotentials at the Counter Electrode by Three-Electrode Coin Cell Measurements

The evaluation of new materials, interfaces, and architectures for battery applications are routinely conducted in two-electrode coin cell experiments, which although convenient, can lead to misrepresentations of the processes occurring in the cell. Few three-electrode coin cell designs have been reported, but those which have involve complex cell assembly, specialized equipment, and/or cell configurations which vary drastically from the standard coin cell environment. Herein, we present a novel, facile three-electrode coin cell design which can be easily assembled with existing coin cell parts and which accurately reproduces the environment of traditional coin cells. Using this design, we systematically investigated the inaccuracies incurred in two-electrode measurements in both symmetric/asymmetric cells and half-cell experiments by galvanostatic charge/discharge, galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry. From our investigation, we reveal that lithium metal stripping contributes larger overpotentials than its nucleation/plating processes, a phenomenon which is often misinterpreted in two-electrode cell measurements.

Electrolyte screening studies for Li metal batteries

From 60 solvent electrolyte combinations tested, we find that Li metal anodes, tested in 1 M LiFSI in DOL:DME exhibit an outstanding cycling performance (>500 cycles) even at high current densities (3 mA cm^-2). The excellent performance is ascribed, at least in part, to a low Li nucleation overpotential and a low charge transfer resistance during cycling.

Cross-linking Effects on Performance Metrics of Phenazine-Based Polymer Cathodes

Developing cathodes that can support high charge-discharge rates would improve the power density of lithium-ion batteries. Herein, the development of high-power cathodes without sacrificing energy density is reported. N,N'-diphenylphenazine was identified as a promising charge-storage center by electrochemical studies due to its reversible, fast electron transfer at high potentials. By incorporating the phenazine redox units in a cross-linked network, a high-capacity (223 mA h g^-1 ), high-voltage (3.45 V vs. Li/Li⁺ ) cathode material was achieved. Optimized cross-linked materials are able to deliver reversible capacities as high as 220 mA h g^-1 at 120 C with minimal degradation over 1000 cycles. The work presented herein highlights the fast ionic transport and rate capabilities of amorphous organic materials and demonstrates their potential as materials with high energy and power density for next-generation electrical energy-storage technologies.

Single Shot Characterization of High Transformer Ratio Wakefields in Nonlinear Plasma Acceleration

Plasma wakefields can enable very high accelerating gradients for frontier high energy particle accelerators, in excess of 10  GeV/m. To overcome limits on single stage acceleration, specially shaped drive beams can be used in both linear and nonlinear plasma wakefield accelerators (PWFA), to increase the transformer ratio, implying that the drive beam deceleration is minimized relative to acceleration obtained in the wake. In this Letter, we report the results of a nonlinear PWFA, high transformer ratio experiment using high-charge, longitudinally asymmetric drive beams in a plasma cell. An emittance exchange process is used to generate variable drive current profiles, in conjunction with a long (multiple plasma wavelength) witness beam. The witness beam is energy modulated by the wakefield, yielding a response that contains detailed spectral information in a single-shot measurement. Using these methods, we generate a variety of beam profiles and characterize the wakefields, directly observing transformer ratios up to R=7.8. Furthermore, a spectrally based reconstruction technique, validated by 3D particle-in-cell simulations, is introduced to obtain the drive beam current profile from the decelerating wake data.

Understanding Conversion-Type Electrodes for Lithium Rechargeable Batteries

The need/desire to lower the consumption of fossil fuels and its environmental consequences has reached unprecedented levels in recent years. A global effort has been undertaken to develop advanced renewable energy generation and especially energy storage technologies, as they would enable a dramatic increase in the effective and efficient use of renewable (and often intermittent) energy sources. The development of electrical energy storage (EES) technologies with high energy and power densities, long life, low cost, and safe use represents a challenge from both the fundamental science and technological application points of view. While the advent and broad deployment of lithium-ion batteries (LIBs) has dramatically changed the EES landscape, their performance metrics need to be greatly enhanced to keep pace with the ever-increasing demands imposed by modern consumer electronics and especially the emerging automotive markets. Current battery technologies are mostly based on the use of a transition metal oxide cathode (e.g., LiCoO₂, LiFePO₄, or LiNiMnCoO₂) and a graphite anode, both of which depend on intercalation/insertion of lithium ions for operation. While the cathode material currently limits the battery capacity and overall energy density, there is a great deal of interest in the development of high-capacity cathode materials as well as anode materials. Conversion reaction materials have been identified/proposed as potentially high-energy-density alternatives to intercalation-based materials. However, conversion reaction materials react during lithiation to form entirely new products, often with dramatically changed structure and chemistry, by reaction mechanisms that are still not completely understood. This makes it difficult to clearly distinguish the limitations imposed by the mechanism and practical losses from initial particle morphology, synthetic approaches, and electrode preparations. Transition metal compounds such as transition metal oxides, sulfides, fluorides, phosphides, and nitrides can undergo conversion reactions yielding materials with high theoretical capacity (generally from 500 to 1500 mA h g^-1). In particular, a number of transition metal oxides and sulfides have shown excellent electrochemical properties as high-capacity anode materials. In addition, some transition metal fluorides have shown great potential as cathode materials for Li rechargeable batteries. In this Account we present mechanistic studies, with emphasis on the use of operando methods, of selected examples of conversion-type materials as both potentially high-energy-density anodes and cathodes in EES applications. We also include examples of the conceptually similar conversion-type reactions involving chalcogens and halogens, with emphasis on the Li-S system. In this case we focus on the problems arising from the low electrical conductivities of elemental sulfur and Li₂S and the "redox shuttle" phenomena of polysulfides. In addition to mechanistic insights from the use of operando methods, we also cover several key strategies in electrode materials design such as controlling the size, morphology, composition, and architecture.

Association between Systolic Blood Pressure after Thrombolysis and Early Neurological Improvement in Ischaemic Stroke Patients

Introduction

This study aimed to evaluate the relationship between systolic blood pressures (SBPs) within 12 hours after intravenous recombinant tissue plasminogen activator (rtPA) treatment and early neurological outcomes.

Methods

This was a retrospective observational study of acute ischaemic stroke (AIS) patients who received intravenous rtPA administration. SBPs at the time of rtPA bolus and thereafter every hour were collected. The mean, standard deviation, and coefficient of variation values of SBP during the periods of 0-2 h, 2-6 h, and 6-12 h were calculated. The primary outcome was major neurologic improvement (MNI) at 24 hours after thrombolysis.

Results

Serial measures of SBPs revealed different 12-hour courses between the patients with and without MNI. The difference of SBP tendency was statistically significant (p=0.013). In univariate analysis, patients with MNI showed lower levels of mean SBPs during the periods of 2-6 h and 6-12 h (p=0.030 and p=0.005, respectively), and higher frequency of very early neurologic improvement (VENI) at the end of rtPA infusion (p<0.001). In logistic regression analysis, VENI at 1 h, mean SBP value during 6-12 h, and atrial fibrillation were independently related to MNI at 24 h.

Conclusions

SBP level during the first 12 hours after intravenous rtPA treatment may be an important clinical factor that is associated with early neurological improvement of AIS patients.

Formation of Thermally Stable Bulk Heterojunction by Reducing the Polymer and Fullerene Intermixing

A morphologically stable bulk heterojunction (BHJ) with a large heterojunction area is prepared by reducing the portion of the small band gap polymer (PTB7) and fullerene intermixture through a sequential deposition (SqD) of the nanostructured PTB7 and the fullerene layer. The nanostructured PTB7 layer is prepared using a ternary solvent composed of chlorobenzene, 1,8-diiodooctane (DIO) and 1-chloronaphthalene (1-CN). Adding DIO and 1-CN enhances the ordering of PTB7 chains and results in a nanostructured polymer surface. The grazing incidence X-ray diffraction results reveal that the SqD of the nanostructured PTB7 and fullerene layers forms the BHJ with little intermixing between the polymer and the fullerene domains compared to the BHJ formed by the deposition of the blended PTB7 and fullerene solution (BSD). The OPV utilizing the SqD processed BHJ (SqD-OPV) exhibits a power conversion efficiency (PCE) of 7.43%, which is similar to that when the BSD processed BHJ (BSD-OPV) is utilized. Furthermore, the SqD-OPV exhibits an excellent thermal stability. The SqD-OPV maintains its initial PCE even after thermal annealing at 140 °C for 10 days, whereas the BSD-OPV maintains 78% of its initial efficiency under the same condition.

Correlation between socio-economic status and atopic dermatitis in Korean adults: the Korea national health and nutrition examination survey (2007-2014)

INTRODUCTION

Atopic dermatitis (AD) is one of the most common allergic diseases. Its prevalence has been increasing in recent decades. Socio-economic status is well-known risk factor of allergic diseases.

OBJECTIVE

This study was performed to investigate the relationship between socio-economic status and AD in Korean adults.

METHODS

Data were acquired from 47 351 men and women, ≥19 years of age who participated in the Korea National Health and Nutrition Examination Surveys (KNHANES) conducted from 2007 to 2014. The presence of AD was based on self-reported physician diagnosis of AD in the Health Interview Surveys.

RESULTS

The prevalence of AD was 3.1%, which decreased with increasing age. In univariate analysis, adults with AD were prone to be female, younger, never-married, well educated, lower household members, and urban dwelling (all P < 0.01). Monthly family income and smoking status were not associated with the presence of AD. The prevalence of hypertension, diabetes mellitus and asthma was higher in AD subjects (all P < 0.01), while obesity was not associated with adult AD. After adjusting for confounders, logistic regression analysis showed female sex (adjusted odds ratio [aOR]: 1.483, 95% CI: 1.268-1.734), age (P < 0.01), marital status (Single: aOR: 1.307, 95% CI: 1.012-1.690; Never-married: aOR: 1.938, 95% CI: 1.513-2.482), urban residence (aOR: 1.281, 95% CI: 1.045-1.569) and asthma (aOR: 1.788, 95% CI: 1.416-2.258) were associated with higher prevalence of AD (all P < 0.01).

CONCLUSION

Female sex, age, marital status, urban residence, and the presence of asthma are important risk factors of the prevalence of AD in Korean adults.

Highly branched RuO2 nanoneedles on electrospun TiO2 nanofibers as an efficient electrocatalytic platform

Highly single-crystalline ruthenium dioxide (RuO2) nanoneedles were successfully grown on polycrystalline electrospun titanium dioxide (TiO2) nanofibers for the first time by a combination of thermal annealing and electrospinning from RuO2 and TiO2 precursors. Single-crystalline RuO2 nanoneedles with relatively small dimensions and a high density on electrospun TiO2 nanofibers are the key feature. The general electrochemical activities of RuO2 nanoneedles-TiO2 nanofibers and Ru(OH)3-TiO2 nanofibers toward the reduction of [Fe(CN)6](3-) were carefully examined by cyclic voltammetry carried out at various scan rates; the results indicated favorable charge-transfer kinetics of [Fe(CN)6](3-) reduction via a diffusion-controlled process. Additionally, a test of the analytical performance of the RuO2 nanoneedles-TiO2 nanofibers for the detection of a biologically important molecule, hydrogen peroxide (H2O2), indicated a high sensitivity (390.1 ± 14.9 μA mM(-1) cm(-2) for H2O2 oxidation and 53.8 ± 1.07 μA mM(-1) cm(-2) for the reduction), a low detection limit (1 μM), and a wide linear range (1-1000 μM), indicating H2O2 detection performance better than or comparable to that of other sensing systems.

High intensity focused ultrasound as a potential new modality for the treatment of pigmentary skin disorder

BACKGROUND/PURPOSE

The clinical skin tightening benefits of high intensity focused ultrasound (HIFU) have been established, but its mechanism of action in pigmented skin disorders remains unknown. We macroscopically and histopathologically investigated dermatological changes after HIFU at different exposure doses in a UVB-induced guinea pig model of hyperpigmentation.

METHODS

We applied HIFU irradiation at 0.1 and 0.2 J/cm(2) to UVB-induced spotty hyperpigmentation in guinea pig skin. The therapeutic effects of HIFU were judged based on gross appearance using photography, dermoscopy, and chromametry during a period of 3 weeks after HIFU irradiation. Histological assessments were performed using Fontana-Masson staining 1 day before and 3 weeks after HIFU irradiation.

RESULTS

Macroscopically, UVB-induced hyperpigmentation was significantly reduced 2 weeks after HIFU with 0.2 J/cm(2) , and 3 weeks after HIFU with 0.1 J/cm(2) . Histopathologically, the heavy deposition of melanin in the epidermis induced by UVB exposure was reduced 3 weeks after HIFU irradiation.

CONCLUSION

We confirmed that HIFU has a positive effect on UVB-induced hyperpigmentation as well as mechanical destructive activity. We suggest that HIFU may be useful as an alternative modality for human patients suffering from skin pigmentary conditions.

Single-crystalline ternary mixed metal oxide 1-dimensional nanostructures of Ir1−x−yRuxVyO2 by vapour phase transport

Highly single-crystalline Ir_1−x−yRu_xV_yO₂ nanowires were grown from metal oxide precursors on a Si wafer by a vapour transport process.

Ruthenium based nanostructures driven by morphological controls as efficient counter electrodes for dye-sensitized solar cells

We introduce a facile approach to use ruthenium dioxide (RuO₂) and ruthenium (Ru) nanostructures as effective counter electrodes instead of using platinum (Pt) for dye-sensitized solar cells (DSSCs).