Female physician-researchers do not achieve career success at the same rate as men. Differences in nonprofessional responsibilities may partially explain this gap.
To investigate the division of ...domestic labor by gender in a motivated group of early-career physician-researchers.
Nationwide postal survey between 2010 and 2011.
United States.
Physician recipients of National Institutes of Health K08 or K23 awards between 2006 and 2009 with active academic affiliation at the time of the survey.
Time spent on parenting and domestic tasks was determined through self-report. Among married or partnered respondents with children, a linear regression model of time spent on domestic activities was constructed considering age, gender, race, specialty, MD or MD/PhD status, age of youngest child, number of children, work hours, K award type, and spousal employment.
A 74% response rate was achieved, and 1049 respondents were academic physicians. Women were more likely than men to have spouses or domestic partners who were employed full-time (85.6% 95% CI, 82.7% to 89.2% vs. 44.9% CI, 40.8% to 49.8%). Among married or partnered respondents with children, after adjustment for work hours, spousal employment, and other factors, women spent 8.5 more hours per week on domestic activities. In the subgroup with spouses or domestic partners who were employed full-time, women were more likely to take time off during disruptions of usual child care arrangements than men (42.6% CI, 36.6% to 49.0% vs. 12.4% CI, 5.4% to 19.5%).
Analyses relied on self-reported data. The study design did not enable investigation of the relationship between domestic activities and professional success.
In this sample of career-oriented professionals, gender differences in domestic activities existed among those with children. Most men's spouses or domestic partners were not employed full-time, which contrasted sharply with the experiences of women.
National Institutes of Health.
The maximum power output and minimum charging time of a lithium-ion battery depend on both ionic and electronic transport. Ionic diffusion within the electrochemically active particles generally ...represents a fundamental limitation to the rate at which a battery can be charged and discharged. To compensate for the relatively slow solid-state ionic diffusion and to enable high power and rapid charging, the active particles are frequently reduced to nanometre dimensions, to the detriment of volumetric packing density, cost, stability and sustainability. As an alternative to nanoscaling, here we show that two complex niobium tungsten oxides-Nb
W
O
and Nb
W
O
, which adopt crystallographic shear and bronze-like structures, respectively-can intercalate large quantities of lithium at high rates, even when the sizes of the niobium tungsten oxide particles are of the order of micrometres. Measurements of lithium-ion diffusion coefficients in both structures reveal room-temperature values that are several orders of magnitude higher than those in typical electrode materials such as Li
Ti
O
and LiMn
O
. Multielectron redox, buffered volume expansion, topologically frustrated niobium/tungsten polyhedral arrangements and rapid solid-state lithium transport lead to extremely high volumetric capacities and rate performance. Unconventional materials and mechanisms that enable lithiation of micrometre-sized particles in minutes have implications for high-power applications, fast-charging devices, all-solid-state energy storage systems, electrode design and material discovery.
Nanostructuring and nanosizing have been widely employed to increase the rate capability in a variety of energy storage materials. While nanoprocessing is required for many materials, we show here ...that both the capacity and rate performance of low-temperature bronze-phase TT- and T-polymorphs of Nb2O5 are inherent properties of the bulk crystal structure. Their unique “room-and-pillar” NbO6/NbO7 framework structure provides a stable host for lithium intercalation; bond valence sum mapping exposes the degenerate diffusion pathways in the sites (rooms) surrounding the oxygen pillars of this complex structure. Electrochemical analysis of thick films of micrometer-sized, insulating niobia particles indicates that the capacity of the T-phase, measured over a fixed potential window, is limited only by the Ohmic drop up to at least 60C (12.1 A·g–1), while the higher temperature (Wadsley–Roth, crystallographic shear structure) H-phase shows high intercalation capacity (>200 mA·h·g–1) but only at moderate rates. High-resolution 6/7Li solid-state nuclear magnetic resonance (NMR) spectroscopy of T-Nb2O5 revealed two distinct spin reservoirs, a small initial rigid population and a majority-component mobile distribution of lithium. Variable-temperature NMR showed lithium dynamics for the majority lithium characterized by very low activation energies of 58(2)–98(1) meV. The fast rate, high density, good gravimetric capacity, excellent capacity retention, and safety features of bulk, insulating Nb2O5 synthesized in a single step at relatively low temperatures suggest that this material not only is structurally and electronically exceptional but merits consideration for a range of further applications. In addition, the realization of high rate performance without nanostructuring in a complex insulating oxide expands the field for battery material exploration beyond conventional strategies and structural motifs.
The nickel-rich layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) is a promising future cathode material for lithium-ion batteries in electric vehicles due to its high specific energy density. However, it ...exhibits fast voltage and capacity fading. In this article, we combine electrochemistry, operando synchrotron X-ray diffraction (XRD), and ex situ solid-state NMR spectroscopy to provide new insights into the structural changes and lithium dynamics of NMC811 during electrochemical charge and discharge, which are essential for a better understanding of its fast degradation. The evolution of the interlayer spacing is tracked by XRD, showing that it gradually increases upon delithiation before collapsing at high state-of-charge (SOC). Importantly, no two-phase O3 → O1 transition is observed at high SOC, demonstrating that this cannot be a major cause of degradation. A strong increase of Li dynamics accompanies the increase of the interlayer spacing, which is shown by 7Li NMR and electrochemical characterization. At high SOC, Li mobility drops considerably, and Li/vacancy ordering can be observed by NMR. A detailed analysis of 7Li NMR spectra at different SOC is provided, demonstrating how Li NMR can be used to extract information on the dynamics of such challenging paramagnetic samples with several hundred different local Li environments. The insights on the evolution of structure and dynamics of NMC811 will further the understanding of its cycling behavior and contribute to the efforts of mitigating its performance fade.
Phosphorus has received recent attention in the context of high-capacity and high-rate anodes for lithium- and sodium-ion batteries. Here, we present a first-principles structure prediction study ...combined with NMR calculations, which gives us insights into its lithiation/sodiation process. We report a variety of new phases found by the ab initio random structure searching (AIRSS) and the atomic species swapping methods. Of particular interest, a stable Na5P4–C2/m structure and locally stable structures found less than 10 meV/f.u. from the convex hull such as Li4P3–P212121, NaP5–Pnma, and Na4P3–Cmcm. The mechanical stability of Na5P4–C2/m and Li4P3–P212121 has been studied by first-principles phonon calculations. We have calculated average voltages, which suggest that black phosphorus (BP) can be considered as a safe anode in lithium-ion batteries due to its high lithium insertion voltage, 1.5 V; moreover, BP exhibits a relatively low theoretical volume expansion compared with other intercalation anodes, 216% (ΔV/V). We identify that specific ranges in the calculated shielding can be associated with specific ionic arrangements, results that play an important role in the interpretation of NMR spectroscopy experiments. Since the lithium-phosphides are found to be insulating even at high lithium concentrations, we show that Li–P-doped phases with aluminum have electronic states at the Fermi level suggesting that using aluminum as a dopant can improve the electrochemical performance of P anodes.
Materials’ Methods: NMR in Battery Research Pecher, Oliver; Carretero-González, Javier; Griffith, Kent J ...
Chemistry of materials,
01/2017, Letnik:
29, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Improving electrochemical energy storage is one of the major issues of our time. The search for new battery materials together with the drive to improve performance and lower cost of existing and new ...batteries is not without its challenges. Success in these matters is undoubtedly based on first understanding the underlying chemistries of the materials and the relations between the components involved. A combined application of experimental and theoretical techniques has proven to be a powerful strategy to gain insights into many of the questions that arise from the “how do batteries work and why do they fail” challenge. In this Review, we highlight the application of solid-state nuclear magnetic resonance (NMR) spectroscopy in battery research: a technique that can be extremely powerful in characterizing local structures in battery materials, even in highly disordered systems. An introduction on electrochemical energy storage illustrates the research aims and prospective approaches to reach these. We particularly address “NMR in battery research” by giving a brief introduction to electrochemical techniques and applications as well as background information on both in and ex situ solid-state NMR spectroscopy. We will try to answer the question “Is NMR suitable and how can it help me to solve my problem?” by shortly reviewing some of our recent research on electrodes, microstructure formation, electrolytes and interfaces, in which the application of NMR was helpful. Finally, we share hands-on experience directly from the lab bench to answer the fundamental question “Where and how should I start?” to help guide a researcher’s way through the manifold possible approaches.
(1)H and (19)F NMR experiments have identified and quantified the internal surface terminations of Ti3C2Tx MXene. -F and -OH terminations are shown to be intimately mixed and there are found to be ...significantly fewer -OH terminations than -F and -O, with the proportions highly dependent on the synthesis method.
The host structure and reversible lithium insertion and extraction of an intercalation compound, TiNb24O62, are described. Neutron diffraction, applied for the first time to TiNb24O62, allowed an ...accurate refinement of the complex block superstructure, particularly with respect to the oxygen sublattice. Analysis of the transition-metal sites revealed significant cation ordering in the mixed-metal oxide. Electrochemical analysis demonstrated highly reversible lithium intercalation with ca. 190 mA·h·g–1 after 100 cycles (C/10 rate, 3 months). The effect of the potential window on the capacity, polarization, and reversibility was carefully examined; a minimum voltage limit of 1.1–1.2 V is critical for efficient and reversible cycling. The galvanostatic intermittent titration technique revealed three solid–solution regions, with different lithium diffusivities, in addition to the two-phase plateau that was clearly observed in the V versus Q discharge/charge profile. Lithium-ion diffusion decreases by over 3 orders of magnitude from the dilute lithium limit early in the discharge to the lithium-stuffed phase Li37.5(1.0)TiNb24O62. Nevertheless, prior to lithium stuffing, TiNb24O62 possesses intrinsically rapid lithium-ion kinetics, as demonstrated by the high-rate performance in thick films of ca. 10 μm particles when interfaced with a carbon-coated aluminum foil substrate. The TiO2·Nb2O5 phase diagram is examined and electrochemical results are compared to related superstructures of crystallographically sheared blocks of octahedra in the TiO2·Nb2O5 homologous series including the H–Nb2O5 end member.
Designing materials with appropriate crystal and electronic structures to enhance ionic and electronic transport simultaneously are highly desirable for both electrochromic and electrochemical energy ...storage devices. It remains a great challenge to simultaneously meet these requirements. Here, a Nb18W16O93 nanomaterial is successfully synthesized with superstructure motifs and uniform self‐supported electrochromic films are prepared on a transparent conductive substrate. The results show that the films can effectively accommodate lithium ions and facilitate intercalation–deintercalation on transparent fluorine‐doped tin oxide (FTO) substrates at high current density. Mechanistic insights into the excellent electrochromic and rechargeable energy storage properties are provided by density functional theory (DFT) calculations. Specifically, the Nb18W16O93 film displays a large optical modulation (up to 93% at 633 nm and 89% at 1200 nm), high coloration efficiency (105.6 cm2 C−1), high energy storage capacity (151.4 mAh g−1 at 2 A g−1), excellent rate capability, and long‐term electrochemical stability (6000 cycles). As a demonstration of its application, an energy storage indicator is illustrated and a complementary electrochromic energy storage smart window is fabricated based on the Nb18W16O93 film. The results demonstrate that the Nb18W16O93 nanomaterial has a promising application in the field of high‐performance electrochromic and energy storage devices.
A Nb18W16O93 nanomaterial with superstructure motifs is found and it is shown that it can effectively accommodate lithium ions and facilitate intercalation–deintercalation. As a result, the Nb18W16O93 film exhibits a robust stability for both electrochromic and rechargeable energy storage applications. Furthermore, an excellent energy‐storage indicator and complementary electrochromic energy storage smart window is fabricated based on the Nb18W16O93 film.
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