6 research outputs found
First-Principles Characterization of the Unknown Crystal Structure and Ionic Conductivity of Li<sub>7</sub>P<sub>2</sub>S<sub>8</sub>I as a Solid Electrolyte for High-Voltage Li Ion Batteries
Using first-principles density functional
theory calculations and
ab initio molecular dynamics (AIMD) simulations, we demonstrate the
crystal structure of the Li<sub>7</sub>P<sub>2</sub>S<sub>8</sub>I
(LPSI) and Li ionic conductivity at room temperature with its atomic-level
mechanism. By successively applying three rigorous conceptual approaches,
we identify that the LPSI has a similar symmetry class as Li<sub>10</sub>GeP<sub>2</sub>S<sub>12</sub> (LGPS) material and estimate the Li
ionic conductivity to be 0.3 mS cm<sup>–1</sup> with an activation
energy of 0.20 eV, similar to the experimental value of 0.63 mS cm<sup>–1</sup>. Iodine ions provide an additional path for Li ion
diffusion, but a strong Li–I attractive interaction degrades
the Li ionic transport. Calculated density of states (DOS) for LPSI
indicate that electrochemical instability can be substantially improved
by incorporating iodine at the Li metallic anode via forming a LiI
compound. Our methods propose the computational design concept for
a sulfide-based solid electrolyte with heteroatom doping for high-voltage
Li ion batteries
First-Principles Study on the Thermal Stability of LiNiO<sub>2</sub> Materials Coated by Amorphous Al<sub>2</sub>O<sub>3</sub> with Atomic Layer Thickness
Using first-principles calculations,
we study how to enhance thermal
stability of high Ni compositional cathodes in Li-ion battery application.
Using the archetype material LiNiO<sub>2</sub> (LNO), we identify
that ultrathin coating of Al<sub>2</sub>O<sub>3</sub> (0001) on LNO(012)
surface, which is the Li de-/intercalation
channel, substantially improves the instability problem. Density functional
theory calculations indicate that the Al<sub>2</sub>O<sub>3</sub> deposits
show phase transition from the corundum-type crystalline (c-Al<sub>2</sub>O<sub>3</sub>) to amorphous (a-Al<sub>2</sub>O<sub>3</sub>) structures as the number of coating layers reaches three. Ab initio
molecular dynamic simulations on the LNO(012) surface coated by a-Al<sub>2</sub>O<sub>3</sub> (about 0.88 nm) with three atomic layers oxygen
gas evolution is strongly suppressed at <i>T</i> = 400 K.
We find that the underlying mechanism is the strong contacting force
at the interface between LNO(012) and Al<sub>2</sub>O<sub>3</sub> deposits,
which, in turn, originated from highly ionic chemical bonding of Al
and O at the interface. Furthermore, we identify that thermodynamic
stability of the a-Al<sub>2</sub>O<sub>3</sub> is even more enhanced
with Li in the layer, implying that the protection for the LNO(012)
surface by the coating layer is meaningful over the charging process.
Our approach contributes to the design of innovative cathode materials
with not only high-energy capacity but also long-term thermal and
electrochemical stability applicable for a variety of electrochemical
energy devices including Li-ion batteries
Universal Scaling Relationship To Screen an Efficient Metallic Adsorbent for Adsorptive Removal of Iodine Gas under Humid Conditions: First-Principles Study
Safe
control and removal of radioactive iodine gases (I-129 and
I-131) leaking from the accidents in chemical factories or nuclear
industries are of importance because of their critical damage to the
biosphere. We study the adsorptive removal of the off-gaseous iodine
using transition metals of group 10 and group 11 under humid conditions.
First-principles calculations enable to capture key adsorption natures
of iodine and water molecules on the adsorbent surfaces. The underlying
mechanism is analyzed by thermodynamic free energies, electronic structures,
and surface work function changes. Our results unveil why silver metal
shows notably outstanding efficiency for the iodine removal. We propose
an innovative and insightful map to guide sorting out the best metal
adsorbents and impregnants for dramatic improvement of the adsorptive
removal of the radioactive iodine gas. Our study is useful for preventing
critical risks from chemical and nuclear accidents
First-Principles Computational Screening of Highly Active Pyrites Catalysts for Hydrogen Evolution Reaction through a Universal Relation with a Thermodynamic Variable
Hydrogen gas has been regarded as
a promising fuel for securing energy and environmental sustainability
of our society. Accordingly, efficient and large scale production
of hydrogen is central issue due to high activation barrier unless
costly transition metal catalysts are used. Here, we screen optimum
catalysts toward hydrogen evolution among cheap pyrites using first-principles
density functional theory calculations and rigorous thermodynamic
approach. A key thermodynamic state variable accurately describes
the catalytic activity, of which the mechanism is unveiled by a universal
linear correlation between kinetic exchange current density in hydrogen
evolution reaction and thermodynamic adsorption energy of hydrogen
atom over various pyrites. On the basis of the results, we propose
a design principle for substantial tuning the catalytic performance
Effect of Activating a Nickel–Molybdenum Catalyst in an Anion Exchange Membrane Water Electrolyzer
Water electrolysis using anion exchange membranes is
promising
for hydrogen production, and Ni–Mo catalysts have shown high
activity for alkaline hydrogen evolution reaction (HER). However,
their performance has been mostly tested in a half-cell setup and
rarely studied in a single-cell setup with a membrane electrode assembly
(MEA) structure, which is used for practical applications. With Ni3Mo as the cathode, a single cell was fabricated using non-noble
metal catalysts exclusively. Interestingly, the activation procedure
significantly affected the cell performance. The single cell performed
better than that with the Pt/C catalyst when the Ni3Mo
catalyst was mildly activated. The distribution of Mo in electrodes,
membrane, and electrolytes was estimated, confirming Mo dissolution
from the cathode. Once the cell was activated, the cell performance
was stable without degradation in long-term chronopotentiometry operation,
but the performance was degraded by sudden voltage change such as
imposing open circuit voltage (OCV). The surface structure and reaction
mechanism were studied with density functional theory: the Mo-dissolved
Ni3Mo(101) surface could promote H2O dissociation,
while MoO3 stably adsorbed on the surface weakened H* adsorption,
promoting HER. This study provides important insights into the development
of efficient catalysts for large-scale hydrogen production
Effective Trapping of Lithium Polysulfides Using a Functionalized Carbon Nanotube-Coated Separator for Lithium–Sulfur Cells with Enhanced Cycling Stability
The
critical issues that hinder the practical applications of lithium–sulfur
batteries, such as dissolution and migration of lithium polysulfides,
poor electronic conductivity of sulfur and its discharge products,
and low loading of sulfur, have been addressed by designing a functional
separator modified using hydroxyl-functionalized carbon nanotubes
(CNTOH). Density functional theory calculations and experimental results
demonstrate that the hydroxyl groups in the CNTOH provoked strong
interaction with lithium polysulfides and resulted in effective trapping
of lithium polysulfides within the sulfur cathode side. The reduction
in migration of lithium polysulfides to the lithium anode resulted
in enhanced stability of the lithium electrode. The conductive nature
of CNTOH also aided to efficiently reutilize the adsorbed reaction
intermediates for subsequent cycling. As a result, the lithium–sulfur
cell assembled with a functional separator exhibited a high initial
discharge capacity of 1056 mAh g<sup>–1</sup> (corresponding
to an areal capacity of 3.2 mAh cm<sup>–2</sup>) with a capacity
fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate