8 research outputs found
Lithium Superionic Sulfide Cathode for All-Solid LithiumāSulfur Batteries
This work presents a facile synthesis approach for coreāshell structured Li<sub>2</sub>S nanoparticles with Li<sub>2</sub>S as the core and Li<sub>3</sub>PS<sub>4</sub> as the shell. This material functions as lithium superionic sulfide (LSS) cathode for long-lasting, energy-efficient lithiumāsulfur (LiāS) batteries. The LSS has an ionic conductivity of 10<sup>ā7</sup> S cm<sup>ā1</sup> at 25 Ā°C, which is 6 orders of magnitude higher than that of bulk Li<sub>2</sub>S (ā¼10<sup>ā13</sup> S cm<sup>ā1</sup>). The high lithium-ion conductivity of LSS imparts an excellent cycling performance to all-solid LiāS batteries, which also promises safe cycling of high-energy batteries with metallic lithium anodes
Artificial Solid Electrolyte Interphase To Address the Electrochemical Degradation of Silicon Electrodes
Electrochemical
degradation on silicon (Si) anodes prevents them
from being successfully used in lithium (Li)-ion battery full cells.
Unlike the case of graphite anodes, the natural solid electrolyte
interphase (SEI) films generated from carbonate electrolytes do not
self-passivate on Si, causing continuous electrolyte decomposition
and loss of Li ions. In this work, we aim at solving the issue of
electrochemical degradation by fabricating artificial SEI films using
a solid electrolyte material, lithium phosphorus oxynitride (Lipon),
which conducts Li ions and blocks electrons. For Si anodes coated
with Lipon of 50 nm or thicker, a significant effect is observed in
suppressing electrolyte decomposition, while Lipon of thinner than
40 nm has a limited effect. Ionic and electronic conductivity measurements
reveal that the artificial SEI is effective when it is a pure ionic
conductor, but electrolyte decomposition is only partially suppressed
when the artificial SEI is a mixed electronicāionic conductor.
The critical thickness for this transition in conducting behavior
is found to be 40ā50 nm. This work provides guidance for designing
artificial SEI films for high-capacity Li-ion battery electrodes using
solid electrolyte materials
Influence of Lithium Salts on the Discharge Chemistry of LiāAir Cells
In this work, we show that the use of a high boiling
point ether
solvent (tetraglyme) promotes the formation of Li<sub>2</sub>O<sub>2</sub> in a lithiumāair cell. However, another major constituent
in the discharge product of a Liāair cell contains halides
from the lithium salts and CāO from the tetraglyme used as
the solvent. This information is critical to the development of Liāair
electrolytes, which are stable and promote the formation of the desired
Li<sub>2</sub>O<sub>2</sub> products
Gold Nanoparticles Supported on Carbon Nitride: Influence of Surface Hydroxyls on Low Temperature Carbon Monoxide Oxidation
This paper reports the synthesis of 2.5 nm gold clusters
on the oxygen free and chemically labile support carbon nitride (C<sub>3</sub>N<sub>4</sub>). Despite having small particle sizes and high
enough water partial pressure these Au/C<sub>3</sub>N<sub>4</sub> catalysts
are inactive for the gas phase and liquid phase oxidation of carbon
monoxide. The reason for the lack of activity is attributed to the
lack of surface āOH groups on the C<sub>3</sub>N<sub>4</sub>. These OH groups are argued to be responsible for the activation
of CO in the oxidation of CO. The importance of basic āOH groups
explains the well documented dependence of support isoelectric point
versus catalytic activity
Unravelling the Impact of Reaction Paths on Mechanical Degradation of Intercalation Cathodes for Lithium-Ion Batteries
The
intercalation compounds are generally considered as ideal electrode
materials for lithium-ion batteries thanks to their minimum volume
expansion and fast lithium ion diffusion. However, cracking still
occurs in those compounds and has been identified as one of the critical
issues responsible for their capacity decay and short cycle life,
although the diffusion-induced stress and volume expansion are much
smaller than those in alloying-type electrodes. Here, we designed
a thin-film model system that enables us to tailor the cation ordering
in LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> spinels and correlate
the stress patterns, phase evolution, and cycle performances. Surprisingly,
we found that distinct reaction paths cause negligible difference
in the overall stress patterns but significantly different cracking
behaviors and cycling performances: 95% capacity retention for disordered
LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> and 48% capacity retention
for ordered LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> after
2000 cycles. We were able to pinpoint that the extended solid-solution
region with suppressed phase transformation attributed to the superior
electrochemical performance of disordered spinel. This work envisions
a strategy for rationally designing stable cathodes for lithium-ion
batteries through engineering the atomic structure that extends the
solid-solution region and suppresses phase transformation
Influence of Hydrocarbon and CO<sub>2</sub> on the Reversibility of LiāO<sub>2</sub> Chemistry Using <i>In Situ</i> Ambient Pressure Xāray Photoelectron Spectroscopy
Identifying fundamental barriers
that hinder reversible lithiumāoxygen
(LiāO<sub>2</sub>) redox reaction is essential for developing
efficient and long-lasting rechargeable LiāO<sub>2</sub> batteries.
Addressing these challenges is being limited by parasitic reactions
in the carbon-based O<sub>2</sub>āelectrode with aprotic electrolytes.
Understanding the mechanisms of these parasitic reactions is hampered
by the complexity that multiple and coupled parasitic reactions involving
carbon, electrolytes, and LiāO<sub>2</sub> reaction intermediates/products
can occur simultaneously. In this work, we employed solid-state cells
free of carbon and aprotic electrolytes to probe the influence of
surface adventitious hydrocarbons and carbon dioxide (CO<sub>2</sub>) on the reversibility of the LiāO<sub>2</sub> redox chemistry
using <i>in situ</i> synchrotron-based ambient pressure
X-ray photoelectron spectroscopy. Direct evidence was provided, for
the first time, that surface hydrocarbons and CO<sub>2</sub> irreversibly
react with LiāO<sub>2</sub> reaction intermediates/products
such as Li<sub>2</sub>O<sub>2</sub> and Li<sub>2</sub>O, forming carboxylate
and carbonate-based species, which cannot be removed fully upon recharge.
The slower Li<sub>2</sub>O<sub>2</sub> oxidation kinetics was correlated
with increasing coverage of surface carbonate/carboxylate species.
Our work critically points out that materials design that mitigates
the reactivity between LiāO<sub>2</sub> reaction products and
common impurities in the atmosphere is needed to achieve long cycle-life
LiāO<sub>2</sub> batteries
Anomalous High Ionic Conductivity of Nanoporous Ī²āLi<sub>3</sub>PS<sub>4</sub>
Lithium-ion-conducting solid electrolytes hold promise
for enabling
high-energy battery chemistries and circumventing safety issues of
conventional lithium batteries. Achieving the combination of high
ionic conductivity and a broad electrochemical window in solid electrolytes
is a grand challenge for the synthesis of battery materials. Herein
we show an enhancement of the room-temperature lithium-ion conductivity
by 3 orders of magnitude through the creation of nanostructured Li<sub>3</sub>PS<sub>4</sub>. This material has a wide electrochemical window
(5 V) and superior chemical stability against lithium metal. The nanoporous
structure of Li<sub>3</sub>PS<sub>4</sub> reconciles two vital effects
that enhance the ionic conductivity: (1) the reduction of the dimensions
to a nanometer-sized framework stabilizes the high-conduction Ī²
phase that occurs at elevated temperatures, and (2) the high surface-to-bulk
ratio of nanoporous Ī²-Li<sub>3</sub>PS<sub>4</sub> promotes
surface conduction. Manipulating the ionic conductivity of solid electrolytes
has far-reaching implications for materials design and synthesis in
a broad range of applications, including batteries, fuel cells, sensors,
photovoltaic systems, and so forth
Structure of Spontaneously Formed Solid-Electrolyte Interphase on Lithiated Graphite Determined Using Small-Angle Neutron Scattering
We address the reactivity of lithiated
graphiteāanode material
for Li-ion batteries with standard organic solvents used in batteries
(ethylene carbonate and dimethyl carbonate) by following changes in
neutron scattering signals. The reaction produces a nanosized layer,
the solid-electrolyte interphase (SEI), on the graphite particles.
We probe the structure and chemistry of the SEI using small-angle
neutron scattering (SANS) and inelastic neutron scattering. The SANS
results show that the SEI fills 20ā30 nm sized pores, and inelastic
scattering experiments with H/D substitution show that this āchemicalā
SEI is primarily organic in nature; that is, it contains a large amount
of hydrogen. The graphiteāSEI particles show surface fractal
scattering characteristic of a rough particleāvoid interface
and are interconnected. The observed changes in the SEI structure
and composition provide new insight into SEI formation. The chemically
formed SEI is complementary and simpler in composition to the electrochemically
formed SEI, which involves a number of different reactions and products
that are difficult to deconvolute