166 research outputs found
High-Performance Lithium Storage Achieved by Chemically Binding Germanium Nanoparticles with N‑Doped Carbon
Germanium (Ge) is a promising anode
material for lithium ion batteries
due to its high theoretical capacity. However, its poor cycling stability
associated with its large volume changes during discharging and charging
processes are urgent problems to solve. This provides opportunities
to engineer materials to overcome these issues. Here, we demonstrated
a facile and scalable method to synthesize Ge nanoparticles/N-doped
carbon monolith with a hierarchically porous structure. The combination
of a solvothermal method and annealing treatment results in a well-connected
three-dimensional N-doped carbon network structure consisting of Ge
nanoparticles firmly coated by the conducting carbon. Such a hierarchical
architecture features multiple advantages, including a continuous
conductive carbon network, binding the Ge nanoparticles with carbon
through a Ge–N chemical bond, and a porous structure for alleviating
volume expansion of Ge particles. When serving as an anode for lithium
ion batteries, the as-formed hybrid displays high capacities up to
1240.3 mAh g<sup>–1</sup> at 0.1 A g<sup>–1</sup> and
813.4 mAh g<sup>–1</sup> at 0.5 A g<sup>–1</sup> after
90 cycles, and at the same time, it also exhibits good cycling stability
and excellent rate capability
Carbon-Anchored MnO Nanosheets as an Anode for High-Rate and Long-Life Lithium-Ion Batteries
Developing electrode materials with
high rate as well as prolonged cycle is particularly necessary for
the ever-growing market penetration of electric vehicles and hybrid
electric vehicle. Herein, we demonstrate a facile and efficient strategy
to synthesize MnO/C hybrid via freeze-drying followed by thermal treatment
in N<sub>2</sub> atmosphere. The MnO nanosheets are firmly anchored
onto carbon layers to form MnO/C hybrid. When used as an anode in
lithium-ion batteries, the typical MnO/C hybrid displays a high initial
Coulombic efficiency of 83.1% and delivers a high capacity of 1449.8
mAh g<sup>–1</sup> after 100 cycles at 0.3 A g<sup>–1</sup>. Furthermore, the typical MnO/C hybrid can still maintain significantly
high capacity of 1467.0 mAh g<sup>–1</sup> after 2000 cycles
at 5 A g<sup>–1</sup>, which may be the best performance reported
so far for MnO-based materials. The superior electrochemical performance
of the MnO/C hybrid may be attributed to its unique microstructure
features such as effective conductive pathway of carbon sheets, firm
connection between MnO and carbon sheets, and small-sized MnO
Core–Shell Bimetallic Carbide Nanoparticles Confined in a Three-Dimensional N‑Doped Carbon Conductive Network for Efficient Lithium Storage
Carbides represent a class of functional materials with unique properties and increasing importance. However, the harsh conditions in conventional synthetic strategies impede subtle control over size and morphology of carbides, which is highly imperative for their practical applications. Herein, we report a facile, simple approach to prepare porous Co<sub>3</sub>ZnC/N-doped carbon hybrid nanospheres. In this structure, the Co<sub>3</sub>ZnC nanoparticles exhibit a core–shell structure and they are uniformly confined in N-doped carbon conductive networks forming rather uniform nanospheres. The hybrid nanospheres have a specific surface area as high as 170.5 m<sup>2</sup> g<sup>–1</sup>. When evaluated as an anode material for lithium ion batteries, they show an excellent lithium storage performance, which can be attributed to the combined effect of the core–shell Co<sub>3</sub>ZnC nanoparticles, the pore structure and the highly conductive and elastic N-doped carbon networks. This work provides an efficient route for the facile production of nanoscale carbides with desirable manipulation over size and morphology for many of important applications
Micro-Intertexture Carbon-Free Iron Sulfides as Advanced High Tap Density Anodes for Rechargeable Batteries
Numerous materials
have been considered as promising electrode materials for rechargeable
batteries; however, developing efficient materials to achieving good
cycling performance and high volumetric energy capacity simultaneously
remains a great challenge. Considering the appealing properties of
iron sulfides, which include low cost, high theoretical capacity,
and favorable electrochemical conversion mechanism, in this work,
we demonstrate the feasibility of carbon-free microscale Fe<sub>1–<i>x</i></sub>S as high-efficiency anode materials for rechargeable
batteries by designing hierarchical intertexture architecture. The
as-prepared intertexture Fe<sub>1–<i>x</i></sub>S
microspheres constructed from nanoscale units take advantage of both
the long cycle life of nanoscale units and the high tap density (1.13
g cm<sup>–3</sup>) of the micro-intertexture Fe<sub>1–<i>x</i></sub>S. As a result, high capacities of 1089.2 mA h g<sup>–1</sup> (1230.8 mA h cm<sup>–3</sup>) and 624.7 mA
h g<sup>–1</sup> (705.9 mA h cm<sup>–3</sup>) were obtained
after 100 cycles at 1 A g<sup>–1</sup> in Li-ion and Na-ion
batteries, respectively, demonstrating one of the best performances
for iron sulfide-based electrodes. Even after deep cycling at 20 A
g<sup>–1</sup>, satisfactory capacities could be retained.
Related results promote the practical application of metal sulfides
as high-capacity electrodes with high rate capability for next-generation
rechargeable batteries
Na Storage Capability Investigation of a Carbon Nanotube-Encapsulated Fe<sub>1–<i>x</i></sub>S Composite
A promising
anode material consisting of Fe<sub>1–<i>x</i></sub>S nanoparticles and bamboo-like carbon nanotubes
(CNTs) has been designed and prepared by an effective in situ chemical
transformation. The resultant Fe<sub>1–<i>x</i></sub>S@CNTs with a three-dimensional network not only provide high conductivity
paths and channels for electrons and ions but also offer the combined
merits of iron sulfide and CNTs in electrochemical energy storage
applications, leading to outstanding performance as an anode material
for sodium-ion batteries. When tested in a half-cell, a high capacity
of 449.2 mAh g<sup>–1</sup> can be retained after 200 cycles
at 500 mA g<sup>–1</sup>, corresponding to a high retention
of 97.4%. Even at 8000 mA g<sup>–1</sup>, a satisfactory capacity
of 326.3 mAh g<sup>–1</sup> can be delivered. When tested in
the full cell, a capacity of 438.5 mAh g<sup>–1</sup> with
capacity retention of 85.0% is manifested after 80 cycles based on
the mass of the anode. The appealing structure and electrochemical
performance of this material demonstrate its great promise for applications
in practical rechargeable batteries
Effects of isoflurane on MAP, CoBF, and DPOAE.
<p>1.15% (isoflurane dose 1), 2.30 vol% (isoflurane dose 2), and 3.45 vol% (isoflurane dose 3) were inhaled for 2 h. A, MAP values. * P<0.05 MAP 20 min after inhalation vs B. # P<0.01 MAP 20 min after inhalation vs B. § P<0.005 MAP 20 min after inhalation vs B. B, CoBF values. * P<0.01 CoBF 25 min after inhalation vs B. # P<0.005 CoBF 25 min after inhalation vs B. C, DPOAE amplitudes. * P<0.01 DPOAE amplitude 2 h after inhalation vs B. # P<0.01 DPOAE amplitude 1 h after the stop of isoflurane dose 2 vs B. § P<0.05 DPOAE amplitude 1 h after the stop of isoflurane dose 3 vs DPOAE amplitude 1 h after the stop of isoflurane dose 2.</p
Economical Synthesis and Promotion of the Electrochemical Performance of Silicon Nanowires as Anode Material in Li-Ion Batteries
Silicon is considered as one of the
most promising anodes
alternative,
with a low voltage and a high theoretical specific capacity of ∼4200
mAh/g, for graphite in lithium-ion batteries. However, the large volume
change and resulting interfacial changes of the silicon during cycling
cause unsatisfactory cycle performance and hinder its commercialization.
In this study, electrochemical performance and interfacial properties
of silicon nanowires (SiNWs) which are prepared by the Cu-catalyzed
chemical vapor deposition method, with 1 M LiPF<sub>6</sub>/EC + DMC
(1:1 v/v) containing 2 wt % or no vinylene carbonate (VC) electrolyte,
are investigated by using
different electrochemical and spectroscopic techniques, i.e., cyclic
voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning
electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS)
techniques. It is shown that the addition of VC has greatly enhanced
the cycling performance and rate capability of SiNWs and should have
an impact on the wide utilization of silicon anode materials in Li-ion
batteries
DNA Catalysis of a Normally Disfavored RNA Hydrolysis Reaction
We recently used in vitro selection
to identify many deoxyribozymes
that catalyze DNA phosphodiester bond hydrolysis and create 5′-phosphate
and 3′-hydroxyl termini. Alternatively, numerous deoxyribozymes
have been identified for catalysis of RNA cleavage by 2′-hydroxyl
transesterification, forming 2′,3′-cyclic phosphate
and 5′-hydroxyl termini. In this study, we investigated the
ability of DNA to catalyze RNA cleavage by hydrolysis rather than
transesterification, although normally the hydrolysis reaction is
substantially disfavored relative to transesterification. Via a series
of in vitro selection experiments, we found that reselection of a
DNA-hydrolyzing deoxyribozyme leads either to transesterification
or hydrolysis, depending on exclusion or inclusion of a stringent
selection pressure for hydrolysis. An entirely new selection starting
from a random DNA pool, using an all-RNA substrate and imposing the
same selection pressure, also leads to RNA hydrolysis. Collectively,
these results establish experimentally that small DNA sequences have
the catalytic ability to direct a chemical reaction down a disfavored
pathway, even when a more favorable mechanism is readily available.
Our view of DNA catalysis is therefore expanded beyond merely increasing
the rates of reactions that would have occurred more slowly without
the catalyst
Scanning electron microscopy observations of OHCs.
<p>OHCs were well-arranged with normal ciliary structure at three doses of propofol (3a, b, c) and 1.15 vol% isoflurane (3d). Following inhalation of 2.30 vol% isoflurane, certain areas of OHCs were disordered and showed swelling and lodging cilia (3e)(marked by arrows). Following inhalation of 3.45 vol% isoflurane, numerous OHCs had disparate cilia and OHCs were absent in some regions (3f) (marked by asterisk).</p
The correlations between age, education and MoCA-BJ cognitive domains and the correlation between cognitive domains and MoCA-BJ total score.
<p>MoCA-BJ, Beijing version of the Montreal Cognitive Assessment</p><p>The correlations between age, education and MoCA-BJ cognitive domains and the correlation between cognitive domains and MoCA-BJ total score.</p
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