4 research outputs found
Sustainable Mesoporous Carbons as Storage and Controlled-Delivery Media for Functional Molecules
Here,
we report the synthesis of surfactant-templated mesoporous carbons
from lignin, which is a biomass-derived polymeric precursor, and their
potential use as a controlled-release medium for functional molecules
such as pharmaceuticals. To the best of our knowledge, this is the
first report on the use of lignin for chemical-activation-free synthesis
of functional mesoporous carbon. The synthesized carbons possess the
pore widths within the range of 2.5â12.0 nm. In this series
of mesoporous carbons, our best result demonstrates a BrunauerâEmmettâTeller
(BET) surface area of 418 m<sup>2</sup>/g and a mesopore volume of
0.34 cm<sup>3</sup>/g, which is twice the micropore volume in this
carbon. Because of the dominant mesoporosity, this engineered carbon
demonstrates adsorption and controlled release of a representative
pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale
utilization of these sustainable mesoporous carbons in applications
involving adsorption, transport, and controlled release of functional
molecules is desired for industrial processes that yield lignin as
a coproduct
Unraveling the Voltage-Fade Mechanism in High-Energy-Density Lithium-Ion Batteries: Origin of the Tetrahedral Cations for Spinel Conversion
High-voltage layered lithium- and
manganese-rich (LMR) oxides have
the potential to dramatically enhance the energy density of current
Li-ion energy storage systems. However, these materials are currently
not used commonly; one reason is their inability to maintain a consistent
voltage profile (voltage fade) during electrochemical cycling. This
report rationalizes the cause of this voltage fade by providing evidence
of layered to spinel (LS) structural evolution pathways in the host
Li<sub>1.2</sub>Mn<sub>0.55</sub>Ni<sub>0.15</sub>Co<sub>0.1</sub>O<sub>2</sub> oxide. By employing neutron powder diffraction, we
show that LS structural rearrangement in the LMR oxide occurs through
a tetrahedral cation intermediate via the following: (i) diffusion
of lithium atoms from octahedral to tetrahedral sites of the lithium
layer [(Li<sub>Li</sub>oct â Li<sub>Li</sub>tet] which is followed
by the dispersal of the lithium ions from the adjacent octahedral
site of the metal layer to the tetrahedral sites of lithium layer
[Li<sub>TM</sub>oct â Li<sub>Li</sub>tet]; (ii) migration of
Mn from the octahedral sites of the transition-metal layer to the
âpermanentâ octahedral site of lithium layer via tetrahedral
site of lithium layer [Mn<sub>TM</sub>oct â Mn<sub>Li</sub>tet â Mn<sub>Li</sub>oct)]. These findings open the door to
potential routes to mitigate this âatomic restructuringâ
in the high-voltage LMR composite oxide by manipulating their composition/structure
for practical use in high-energy-density lithium-ion batteries
Neutron Diffraction and Magnetic Susceptibility Studies on a High-Voltage Li<sub>1.2</sub>Mn<sub>0.55</sub>Ni<sub>0.15</sub>Co<sub>0.10</sub>O<sub>2</sub> Lithium Ion Battery Cathode: Insight into the Crystal Structure
Lithium- and manganese-rich oxides
undergo structural transformation
and/or atomic rearrangements during the delithiation/lithiation process
and ultimately suffer from several issues such as first cycle irreversible
capacity and voltage fade. In order to understand the mechanism of
these issues, perception of a detailed crystal structure of pristine
material is obviously demanding. In this study, combined powder neutron
diffraction (ND) and temperature-dependent magnetic susceptibility
techniques were employed to investigate the structure of a pristine
lithium- and manganese-rich Li<sub>1.2</sub>Mn<sub>0.55</sub>Ni<sub>0.15</sub>Co<sub>0.10</sub>O<sub>2</sub> cathode oxide. Rietveld
refinement on the experimental ND pattern yields good fits by considering
either Li<sub>2</sub>MO<sub>3</sub> (M = Co, Mn, Ni) type monoclinic
(<i>C2/m</i> space group) phase with 1% of Ni residing in
the 4h lithium site or a composite structure consisting of 50% of
Li<sub>2</sub>MnO<sub>3</sub> type monoclinic (<i>C2/m</i> space group) and 50% LiMO<sub>2</sub> (M = Co, Mn, Ni) type trigonal
(<i>R</i>3Ě
<i>m</i> space group) structure.
In the composite structure, 3% Li/Ni site exchange in the trigonal
phase is also proposed. Further, temperature-dependent dc magnetic
susceptibility shows CurieâWeiss paramagnetic behavior at <i>T</i> ⼠100 K, and no ordering/deviation of the field
cooling (FC) curve in the temperature range 2â320 K indicates
the random distribution of metal ions in the transition metal (TM)
layer in the trigonal phase. Bifurcation of the zero-field cooling
(ZFC) curve from the FC curve showing a magnetic ordering at <i>T</i><sub>N</sub><i> âź</i> 50 K reveals the
presence of cation ordering in the TM layers arising from a distinct
Li<sub>2</sub>MnO<sub>3</sub>-like phase. These results suggest that
the lithium- and manganese-rich oxide with a composition Li<sub>1.2</sub>Mn<sub>0.55</sub>Ni<sub>0.15</sub>Co<sub>0.10</sub>O<sub>2</sub> is
more likely a composite of monoclinic and trigonal phases. The report
also highlights the unique materials diagnostic capability of combined
ND and magnetic susceptibility techniques to obtain detailed structural
information of complex oxide systems
Anomalous High Ionic Conductivity of Nanoporous βâLi<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 β
phase that occurs at elevated temperatures, and (2) the high surface-to-bulk
ratio of nanoporous β-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