1,210 research outputs found
Revealing the formation and electrochemical properties of bis(trifluoromethanesulfonyl) imide intercalated graphite with first-principles calculations
Graphite has been reported to have anion as well as cation intercalation
capacities as both cathode and anode host materials for the dual ion battery.
In this work, we study the intercalation of bis(trifluoromethanesulfonyl) imide
(TFSI) anion from ionic liquid electrolyte into graphite with first-principles
calculations. We build models for TFSI-C compounds with systematically
increasing unit cell sizes of graphene sheet and investigate their stabilities
by calculating the formation energy, resulting in the linear decrease and
arriving at the limit of stability. With identified unit cell sizes for stable
compound formation, we reveal that the interlayer distance and relative volume
expansion ratio of TFSI-C increase as increasing the concentration of TFSI
intercalate during the charge process. The electrode voltage is determined to
be ranged from 3.8 V to 3.0 V at the specific capacity ranging from 30 mAh
g to 54 mAh g in agreement with experiment. Moreover, a very low
activation barrier of under 50 meV for TFSI migration and good electronic
conductivity give a proof of using these compounds as a promising cathode.
Through the analysis of charge transfer, we clarify the mechanism of TFSI-C
formation, and reveal new prospects for developing graphite based cathode
Ab initio study of sodium cointercalation with diglyme molecule into graphite
The cointercalation of sodium with the solvent organic molecule into graphite
can resolve difficulty of forming the stage-I Na-graphite intercalation
compound, which is a predominant anode of Na-ion battery. To clarify the
mechanism of such cointercalation, we investigate the atomistic structure,
energetics, electrochemical properties, ion and electron conductance, and
charge transferring upon de/intercalation of the solvated Na-diglyme ion into
graphite with {\it ab initio} calculations. It is found that the
Na(digl)C compound has the negatively lowest intercalation energy at
21, the solvated Na(digl) ion diffuses fast in the interlayer
space, and their electronic conductance can be enhanced compared to graphite.
The calculations reveal that the diglyme molecules as well as Na atom donates
electrons to the graphene layer, resulting in the formation of ionic bonding
between the graphene layer and the moiety of diglyme molecule. This work will
contribute to the development of innovative anode materials for alkali-ion
battery applications
Ab initio investigation of the adsorption of zoledronic acid molecule on hydroxyapatite (001) surface: an atomistic insight of bone protection
We report a computational study of the adsorption of zoledronic acid molecule
on hydroxyapatite (001) surface within ab initio density functional theory. The
systematic study has been performed, from hydroxyapatite bulk and surface, and
zoledronic acid molecule to the adsorption of the molecule on the surface. The
optimized bond lengths and bond angles were obtained and analyzed, giving an
evidence of structural similarity between subjects under study. The formation
energies of hydroxyapatite (001) surfaces with two kinds of terminations were
computed as about 1.2 and 1.5 J/m^2 with detailed atomistic structural
information. We determined the adsorption energies of zoledronic acid molecule
on the surfaces, which are -260 kJ/mol at 0.25 ML and -400 kJ/mol at 0.5 ML. An
atomistic insight of strong binding affinity of zoledronic acid to the
hydroxyapatite surface was given and discussed.Comment: 11 pages, 8 figure
Influence of halide composition on the structural, electronic, and optical properties of mixed CHNHPb(IBr) perovskites calculated using the virtual crystal approximation method
We investigate the structural, electronic and optical properties of mixed
bromide-iodide lead perovskite solar cell CHNHPb(IBr)
by means of the virtual crystal approximation (VCA) within density functional
theory (DFT). Optimizing the atomic positions and lattice parameters increasing
the bromide content from 0.0 to 1.0, we fit the calculated lattice
parameter and energy band gap to the linear and quadratic function of Br
content, respectively, which are in good agreement with the experiment,
respecting the Vegard's law. With the calculated exciton binding energy and
light absorption coefficient, we make sure that VCA gives consistent results
with the experiment, and the mixed halide perovskites are suitable for
generating the charge carriers by light absorption and conducting the carriers
easily due to their strong photon absorption coefficient, low exciton bindign
energy, and high carrier mobility at low Br contents. Furthermore analyzing the
bonding lengths between Pb and X (IBr: virtual atom) as well as C
and N, we stress that the stability of perovskite solar cell is definitely
improved at =0.2
Ab initio Investigation of Adsorption Characteristics of Bisphosphonates on Hydroxyapatite (001) Surface
The structures of some bisphosphonates (clodronate, etidronate, pamidronate,
alendronate, risedronate, zoledronate, minodronate) were obtained and analyzed,
and their adsorption energies onto hydroxyapatite (001) surface were compared
to find out ranking order of binding affinity, which shows that the adsorption
energy is the largest for pamidronate, followed by alendronate, zoledronate,
clodronate, ibandronate, the lowest for minodronate and etidronate
Two-dimensional hybrid composites of SnS2 with graphene and graphene oxide for improving sodium storage: A first-principles study
Among the recent achievements of sodium-ion battery (SIB) electrode
materials, hybridization of two-dimentional (2D) materials is one of the most
interesting appointments. In this work, we propose to use the 2D hybrid
composites of SnS2 with graphene or graphene oxide (GO) layers as SIB anode,
based on the first-principles calculations of their atomic structures, sodium
intercalation energetics and electronic properties. The calculations reveal
that graphene or GO film can effectively support not only the stable formation
of hetero-interface with the SnS2 layer but also the easy intercalation of
sodium atom with low migration energy and acceptable low volume change. The
electronic charge density differences and the local density of state indicate
that the electrons are transferred from the graphene or GO layer to the SnS2
layer, facilitating the formation of hetero-interface and improving the
electronic conductance of the semiconducting SnS2 layer. These 2D hybrid
composites of SnS2/G or GO are concluded to be more promising candidates for
SIB anodes compared with the individual monolayers
First-principles study of ternary graphite compounds cointercalated with alkali atoms (Li, Na, and K) and alkylamines towards alkali ion battery applications
Using density functional theory calculations, we have investigated the
structural, energetic, and electronic properties of ternary graphite
intercalation compounds (GICs) containing alkali atoms (AM) and normal
alkylamine molecules (nC), denoted as AM-nC-GICs (AM=Li, Na, K, =1, 2,
3, 4). The orthorhombic unit cells have been used to build the models for
crystalline stage-I AM-nC-GICs. By performing the variable cell relaxations
and the analysis of results, we have found that with the increase in the atomic
number of alkali atoms the layer separations decreases in contrast to AM-GICs,
while the bond lengths of alkali atoms with graphene layer and nitrogen atom of
alkylamine decreases. The formation and interlayer binding energies of
AM-nC3-GICs have been calculated, indicating the increase in stability from Li
to K. The calculated energy barriers for migration of alkali atoms suggest that
alkali cation with larger ionic radius diffuses in graphite more smoothly,
being similar to AM-GICs. The analysis of density of states, electronic density
differences, and atomic populations illustrates a mechanism how the insertion
of especially Na among alkali atoms into graphite with first stage can be made
easy by cointercalation with alkylamine, more extent of electronic charge
transfer is occurred from more electropositive alkali atom to carbon ring of
graphene layer, while alkylamine molecules interact strongly with graphene
layer through the hybridization of valence electron orbitals.Comment: 22 pages, 9 figure
Ionic Diffusion and Electronic Transport in Eldfellite NaFe(SO)
Discovering new electrodes for sodium-ion battery requires clear
understanding of the material process during battery operation. Using
first-principles calculations, we identify mechanisms of ionic diffusion and
electronic transfer in newly developed cathode material, eldfellite
NaFe(SO), reproducing the electrochemical properties in good
agreement with experiment. The inserted sodium atom is suggested to diffuse
along the two-dimensional pathway with preceding movement of the host sodium
atom, and the activation energy is calculated to be reasonable for fast
insertion. We calculate the electronic properties, showing the band insulating
at low composition of inserted sodium, for which the electron polaron formation
and hoping are also suggested. Our results may contribute to opening a new way
of developing innovative cathode materials based on iron and sulfate ion
Defect energetics and electronic structures of As-doped p-type ZnO crystals: A first-principles study
First-principles calculations based on density functional theory have been
carried out to understand the mechanism of fabricating As-doped p-type ZnO
semiconductors. It has been confirmed that AsZn-2VZn complex is the most
plausible acceptor among several candidates for p-type doping by computing the
formation and ionization energies. The electronic band structures and
atomic-projected density of states of AsZn-2VZn defect complex-contained ZnO
bulks have been computed. The acceptor level in AsZn-2VZn band structure has
found to be 0.12 eV, which is in good agreement with the experimental
ionization energy (0.12 ~ 0.18 eV). The hybridization among O 2p, Zn 3d and As
4s states has been observed around the valence band maximum
Role of Water Molecule in Enhancing the Proton Conductivity on Graphene Oxide at Humidity Condition
Recent experimental reports on in-plane proton conduction in reduced graphene
oxide (rGO) films open a new way for the design of proton exchange membrane
essential in fuel cells and chemical filters. At high humidity condition, water
molecules attached on the rGO sheet are expected to play a critical role, but
theoretical works for such phenomena have been scarcely found in the
literature. In this study, we investigate the proton migration on
water-adsorbed monolayer and bilayer rGO sheets using first-principles
calculations in order to reveal the mechanism. We devise a series of models for
the water-adsorbed rGO films as systematically varying the reduction degree and
water content, and optimize their atomic structures in reasonable agreement
with the experiment, using a density functional that accounts for van der Waals
correction. Upon suggesting two different transport mechanisms, epoxy-mediated
and water-mediated hoppings, we determine the kinetic activation barriers for
these in-plane proton transports on the rGO sheets. Our calculations indicate
that the water-mediated transport is more likely to occur due to its much lower
activation energy than the epoxy-mediated one and reveal new prospects for
developing efficient solid proton conductors
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