3,919 research outputs found
Simulation of gaseous core nuclear rocket mixing characteristics using cold and arc heated flows
Mixing phenomena of cold and arc heated jets from coaxial flows of helium or nitrogen related to gaseous core nuclear rocket
Thermodynamically stable lithium silicides and germanides from density-functional theory calculations
Density-functional-theory (DFT) calculations have been performed on the Li-Si
and Li-Ge systems. Lithiated Si and Ge, including their metastable phases, play
an important technological r\^ole as Li-ion battery (LIB) anodes. The
calculations comprise structural optimisations on crystal structures obtained
by swapping atomic species to Li-Si and Li-Ge from the X-Y structures in the
International Crystal Structure Database, where X={Li,Na,K,Rb,Cs} and
Y={Si,Ge,Sn,Pb}. To complement this at various Li-Si and Li-Ge stoichiometries,
ab initio random structure searching (AIRSS) was also performed. Between the
ground-state stoichiometries, including the recently found LiSi
phase, the average voltages were calculated, indicating that germanium may be a
safer alternative to silicon anodes in LIB, due to its higher lithium insertion
voltage. Calculations predict high-density LiSi and LiGe
layered phases which become the ground state above 2.5 and 5 GPa
respectively and reveal silicon and germanium's propensity to form dumbbells in
the LiSi, stoichiometry range. DFT predicts the stability of
the LiGe , LiGe and LiGe
phases and several new Li-Ge compounds, with stoichiometries LiGe,
LiGe, LiGe and LiGe.Comment: 10 pages, 5 figure
Joint NMR and Diffraction Studies of Catalyst Structure and Binding
See uploaded final report
Energetics of hydrogen/lithium complexes in silicon analyzed using the Maxwell construction
We have studied hydrogen/lithium complexes in crystalline silicon using
density-functional-theory methods and the ab initio random structure searching
(AIRSS) method for predicting structures. A method based on the Maxwell
construction and convex hull diagrams is introduced which gives a graphical
representation of the relative stabilities of point defects in a crystal and
enables visualization of the changes in stability when the chemical potentials
are altered. We have used this approach to study lithium and hydrogen
impurities in silicon, which models aspects of the anode material in the
recently-suggested lithium-ion batteries. We show that hydrogen may play a role
in these anodes, finding that hydrogen atoms bind to three-atom lithium
clusters in silicon, forming stable {H,3Li} and {2H,3Li} complexes, while the
{H,2Li} complex is almost stable.Comment: (5 pages, 4 figures
Capturing the spark: PISA, twenty-first century skills and the reconstruction of creativity
Creativity has fascinated scholars for generations, and its identification as one of the key ‘twenty-first century skills' necessary for economic growth has led to renewed interest. This creates two challenges for the OECD: its flagship Programme of International Student Assessment (PISA) does not directly measure creativity. Secondly, the increased importance attached to creativity has highlighted claims that high performers on PISA are largely nations stereotyped as lacking creativity. This challenges PISA's self-proclaimed status as the premier global benchmark for evaluating and comparing the quality of school systems and weakens its capacity to deliver its core mission; to identify ‘best practices' which ensure economic prosperity. We explore these challenges and examine both how the OECD has responded to them and is moving to include creativity in PISA 2022. We argue that, while a precise definition of creativity has defied scholars for centuries, the indications are that the OECD's metric will focus on a narrow, convergent and easily-measured conception associated with cognitive competencies and linked to enhancing human capital. In this way, the ‘messiness’ around the polysemic concept will be simultaneously both exploited and threatened, as new, measurable versions displace alternatives
Lithiation of silicon via lithium Zintl-defect complexes
An extensive search for low-energy lithium defects in crystalline silicon
using density-functional-theory methods and the ab initio random structure
searching (AIRSS) method shows that the four-lithium-atom substitutional point
defect is exceptionally stable. This defect consists of four lithium atoms with
strong ionic bonds to the four under-coordinated atoms of a silicon vacancy
defect, similar to the bonding of metal ions in Zintl phases. This complex is
stable over a range of silicon environments, indicating that it may aid
amorphization of crystalline silicon and form upon delithiation of the silicon
anode of a Li-ion rechargeable battery.Comment: 4 pages, 3 figure
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High-rate lithium ion energy storage to facilitate increased penetration of photovoltaic systems in electricity grids
High-rate lithium ion batteries can play a critical role in decarbonizing our energy systems both through their underpinning of the transition to use renewable energy resources such as photovoltaics and electrification of transport. Their ability to be rapidly and frequently charged and discharged can enable this energy storage technology to play a key role in facilitating future lowcarbon electricity networks and thereby limit emissions that may result from transport electrification if fossil fuels are required for battery production and charging. This decarbonizing transition will require lithium ion technology to provide increased power and longer cycle lives at reduced cost. Rate performance and cycle life are ultimately limited by the materials used and the kinetics associated with the charge transfer reactions, ionic and electronic conduction. We review materials strategies for electrode materials and electrolytes that can facilitate high rates and long cycle lives and explore the new opportunities that may arise in embedded distributed storage via devices that blur the distinction between supercapacitors and batteries.This work has been supported by the Australian Research Council (ARC) through grants DP170103219 and FT170100447 (Future Fellowship – Alison Lennon). Yu Jiang and Charles Hall acknowledge the support of the Australian Government through their Research Training Program Scholarships. Kent J. Griffith acknowledges funding from the Winston Churchill Foundation of the United States and a Herchel Smith Scholarship. Kent J. Griffith and Clare P. Grey thank the EPSRC for a LIBATT grant (EP/M009521/1). The views expressed herein are not necessarily the views of the Australian Government, and the Australian Government does not accept responsibility for any information or advice contained herein
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Prospects for lithium-ion batteries and beyond-a 2030 vision.
It would be unwise to assume ‘conventional’ lithium-ion batteries are approaching the end of their era and so we discuss current strategies to improve the current and next generation systems, where a holistic approach will be needed to unlock higher energy density while also maintaining lifetime and safety. We end by briefly reviewing areas where fundamental science advances will be needed to enable revolutionary new battery systems
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