18 research outputs found
Iso-Oriented NaTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> Mesocrystals as Anode Material for High-Energy and Long-Durability Sodium-Ion Capacitor
Sodium-ion
capacitors (SIC) combine the merits of both high-energy batteries
and high-power electrochemical capacitors as well as the low cost
and high safety. However, they are also known to suffer from the severe
deficiency of suitable electrode materials with high initial Coulombic
efficiency (ICE) and kinetic balance between both electrodes. Herein,
we report a facile solvothermal synthesis of NaTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> nanocages constructed by iso-oriented tiny nanocrystals
with a mesoporous architecture. It is notable that the NaTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> mesocrystals exhibit a large ICE of
94%, outstanding rate capability (98 mA h g<sup>ā1</sup> at
10 C), and long cycling life (over 77% capacity retention after 10āÆ000
cycles) in half cells, all of which are in favor to be utilized into
a full cell. When assembled with commercial activated carbon to an
SIC, the system delivers an energy density of 56 Wh kg<sup>ā1</sup> at a power density of 39 W kg<sup>ā1</sup>. Even at a high
current rate of 5 A g<sup>ā1</sup> (corresponds to finish a
full charge/discharge process in 2 min), the SIC still works well
after 20āÆ000 cycles without obvious capacity degradation. With
the merits of impressive energy/power densities and longevity, the
obtained hybrid capacitor should be a promising device for highly
efficient energy storage systems
Hollow Ball-in-Ball Co<sub><i>x</i></sub>Fe<sub>3ā<i>x</i></sub>O<sub>4</sub> Nanostructures: High-Performance Anode Materials for Lithium-Ion Battery
The intrinsic electronic conductivity
can be improved by doping efficiently. Co<sub><i>x</i></sub>Fe<sub>3ā<i>x</i></sub>O<sub>4</sub> nanostructures
have been synthesized for the first time to improve the conductivity
of lithium battery electrode. The solid solution Co<sub><i>x</i></sub>Fe<sub>3ā<i>ā</i>x</sub>O<sub>4</sub> were characterized by X-ray diffraction pattern (XRD), Raman spectrum,
scanning electron microscopy (SEM), transmission electron microscope
(TEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry
(CV). The results show that the doping enlarge the lattice spacing
but the structure of Co<sub>3</sub>O<sub>4</sub> is stable in the
Li-ion intercalation/deintercalation process. The AC impedance spectrum
reveals the conductivity is well improved. In addition, the solid
solution Co<sub><i>x</i></sub>Fe<sub>3ā<i>x</i></sub>O<sub>4</sub> exhibit excellent electrochemical characteristics.
The electrodes with 20% molar ratio of Fe ions own a reversible capacity
of 650.2 mA h g<sup>ā1</sup> at a current density of 1 A g<sup>ā1</sup> after 100 cycles
Fast and Universal Approach to Encapsulating Transition Bimetal Oxide Nanoparticles in Amorphous Carbon Nanotubes under an Atmospheric Environment Based on the Marangoni Effect
Transition
metal oxide nanoparticles capsuled in amorphous carbon nanotubes (ACNTs)
are attractive anode materials of lithium-ion batteries (LIBs). Here,
we first designed a fast and universal method with a hydromechanics
conception which is called Marangoni flow to fabricate transition
bimetal oxides (TBOs) in the ACNT composite with a better electrochemistry
performance. Marangoni flows can produce a liquid column with several
centimeters of height in a tube with one side immersed in the liquid.
The key point to induce a Marangoni flow is to make a gradient of
the surface tension between the surface and the inside of the solution.
With our research, we control the gradient of the surface tension
by controlling the viscosity of a solution. To show how our method
could be generally used, we synthesize two anode materials such as
(a) CoFe<sub>2</sub>O<sub>4</sub>@ACNTs, and (b) NiFe<sub>2</sub>O<sub>4</sub>@ACNTs. All of these have a similar morphology which is ā¼20
Ī¼m length with a diameter of 80ā100 nm for the ACNTs,
and the particles (inside the ACNTs) are smaller than 5 nm. In particular,
there are amorphous carbons between the nanoparticles. All of the
composite materials showed an outstanding electrochemistry performance
which includes a high capacity and cycling stability so that after
600 cycles the capacity changed by less than 3%
Embedded into Graphene Ge Nanoparticles Highly Dispersed on Vertically Aligned Graphene with Excellent Electrochemical Performance for Lithium Storage
Decreasing
particle size has always been reported to be an efficient
way to improve cyclability of Li-alloying based LIBs. However, nanoparticles
(NPs) tend to agglomerate and evolve into lumps, which in turn limits
the cycling performance. In this report, we prepared a unique nanostructure,
graphene-coated Ge NPs are highly dispersed on vertically aligned
graphene (Ge@graphene/VAGN), to avoid particle agglomeration and pulverization.
Remarkable structure stability of the sample leads to excellent cycling
stability. Upon cycling, the anode exhibits a high capacity of 1014
mAh g<sup>ā1</sup>, with nearly no capacity loss in 90 cycles.
Rate performance shows that even at the high current density of 13
A g<sup>ā1</sup>, the anode could still deliver a higher capacity
than that of graphite
Flexible Transparent and Free-Standing Silicon Nanowires Paper
If the flexible transparent and free-standing
paper-like materials
that would be expected to meet emerging technological demands, such
as components of transparent electrical batteries, flexible solar
cells, bendable electronics, paper displays, wearable computers, and
so on, could be achieved in silicon, it is no doubt that the traditional
semiconductor materials would be rejuvenated. Bulk silicon cannot
provide a solution because it usually exhibits brittleness at below
their melting point temperature due to high Peierls stress. Fortunately,
when the siliconās size goes down to nanoscale, it possesses
the ultralarge straining ability, which results in the possibility
to design flexible transparent and self-standing silicon nanowires
paper (FTS-SiNWsP). However, realization of the FTS-SiNWsP is still
a challenging task due largely to the subtlety in the preparation
of a unique interlocking alignment with free-catalyst controllable
growth. Herein, we present a simple synthetic strategy by gas flow
directed assembly of a unique interlocking alignment of the Si nanowires
(SiNWs) to produce, for the first time, the FTS-SiNWsP, which consisted
of interconnected SiNWs with the diameter of ā¼10 nm via simply
free-catalyst thermal evaporation in a vertical high-frequency induction
furnace. This approach opens up the possibility for creating various
flexible transparent functional devices based on the FTS-SiNWsP
CuFeS<sub>2</sub> Quantum Dots Anchored in Carbon Frame: Superior Lithium Storage Performance and the Study of Electrochemical Mechanism
Herein,
we report a simple and quick synthetic route to prepare the pure CuFeS<sub>2</sub> quantum dots (QDs) @C composites with the unique structure
of CuFeS<sub>2</sub> QDs encapsulated in the carbon frame. When tested
as anode materials for the lithium ion battery, the CuFeS<sub>2</sub> QDs @C composites based electrodes exhibit excellent electrochemical
performances. When chargeādischarge occurred with a current
density of 0.5 A g<sup>ā1</sup>, the electrodes exhibit a high
reversible capacity (760 mA h g<sup>ā1</sup>) for as long as
700 cycles, which indicates the superior cycling life. Detailed investigations
of the morphological and structural changes of CuFeS<sub>2</sub> QDs
by ex situ XRD, ex situ Raman, and ex situ TEM reveal an interesting
electrochemical reaction mechanism, a hybrid of a lithiumācopper
iron sulfide battery and lithiumāsulfur battery. The direct
observation of orthorhombic FeS<sub>2</sub> by HRTEM and the existence
of Li<sub>2</sub>FeS<sub>2</sub> detected by Raman support our assertion.
We believe such an electrochemical mechanism would attract more attention
to the CuFeS<sub>2</sub> nanomaterials as lithium ion battery anode
materials. The excellent electrochemical properties would be derived
from the unique structure, which include CuFeS<sub>2</sub> QDs encapsulated
in the carbon frame
Self-Climbed Amorphous Carbon Nanotubes Filled with Transition Metal Oxide Nanoparticles for Large Rate and Long Lifespan Anode Materials in Lithium Ion Batteries
A composed
material of amorphous carbon nanotubes (ACNTs) and encapsulated transition
metal oxide (TMOs) nanoparticles was prepared by a common thermophysics
effect, which is named the Marangoni effect, and a simple anneal process.
The prepared ropy solution would form a Marangoni convection and climb
into the channel of anodic aluminum oxide template (AAO) spontaneously.
The ingenious design of the preparation method determined a distinctive
structure of TMOs nanoparticles with a size of ā¼5 nm and amorphous
carbon coated outside full in the ACNTs. Here we prepared the ferric
oxide (Fe<sub>2</sub>O<sub>3</sub>) nanoparticles and Fe<sub>2</sub>O<sub>3</sub> mixed with manganic oxide (Fe<sub>2</sub>O<sub>3</sub>&Mn<sub>2</sub>O<sub>3</sub>) nanoparticles encapsulated in ACNTs
as two anode materials of lithium ion batteriesā the TMOs-filled
ACNTs presented an evolutionary electrochemical performance in some
respects of highly reversible capacity and excellent cycling stability
(880 mA h g<sup>ā1</sup> after 150 cycles)
Amorphous ZnO Quantum Dot/Mesoporous Carbon Bubble Composites for a High-Performance Lithium-Ion Battery Anode
Due to its high theoretical
capacity (978 mA h g<sup>ā1</sup>), natural abundance, environmental
friendliness, and low cost, zinc
oxide is regarded as one of the most promising anode materials for
lithium-ion batteries (LIBs). A lot of research has been done in the
past few years on this topic. However, hardly any research on amorphous
ZnO for LIB anodes has been reported despite the fact that the amorphous
type could have superior electrochemical performance due to its isotropic
nature, abundant active sites, better buffer effect, and different
electrochemical reaction details. In this work, we develop a simple
route to prepare an amorphous ZnO quantum dot (QDs)/mesoporous carbon
bubble composite. The composite consists of two parts: mesoporous
carbon bubbles as a flexible skeleton and monodisperse amorphous zinc
oxide QDs (smaller than 3 nm) encapsulated in an amorphous carbon
matrix as a continuous coating tightly anchored on the surface of
mesoporous carbon bubbles. With the benefits of abundant active sites,
amorphous nature, high specific surface area, buffer effect, hierarchical
pores, stable interconnected conductive network, and multidimensional
electron transport pathways, the amorphous ZnO QD/mesoporous carbon
bubble composite delivers a high reversible capacity of nearly 930
mA h g<sup>ā1</sup> (at current density of 100 mA g<sup>ā1</sup>) with almost 90% retention for 85 cycles and possesses a good rate
performance. This work opens the possibility to fabricate high-performance
electrode materials for LIBs, especially for amorphous metal oxide-based
materials
Germanium Nanowires-in-Graphite Tubes <i>via</i> Self-Catalyzed Synergetic Confined Growth and Shell-Splitting Enhanced Li-Storage Performance
Despite the high theoretical capacity, pure Ge has various difficulties such as significant volume expansion and electron and Li<sup>+</sup> transfer problems, when applied as anode materials in lithium ion battery (LIB), for which the solution would finally rely on rational design like advanced structures and available hybrid. Here in this work, we report a one-step synthesis of Ge nanowires-in-graphite tubes (GNIGTs) with the liquid Ge/C synergetic confined growth method. The structure exhibits impressing LIB behavior in terms of both cyclic stability and rate performance. We found the semiclosed graphite shell with thickness of ā¼50 layers experience an interesting splitting process that was driven by electrolyte diffusion, which occurs before the GeāLi alloying plateau begins. Two types of different splitting mechanism addressed as āinside-outā/zipper effect and āoutside-inā dominate this process, which are resulted from the SEI layer growing longitudinally along the Geāgraphite interface and the lateral diffusion of Li<sup>+</sup> across the shell, respectively. The former mechanism is the predominant way driving the initial shell to split, which behaves like a zipper with SEI layer as invisible puller. After repeated Li<sup>+</sup> insertion/exaction, the GNIGTs configuration is finally reconstructed by forming Ge nanowiresāthin graphite strip hybrid, both of which are in close contact, resulting in enormous enchantment to the electrons/Li<sup>+</sup> transport. These features make the structures perform well as anode material in LIB. We believe both the progress in 1D assembly and the structure evolution of this GeāC composite would contribute to the design of advanced LIB anode materials
Plasma-Assisted Synthesis of Self-Supporting Porous CoNPs@C Nanosheet as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting
The
utilization of a highly active and robust bifunctional catalyst for
simultaneously producing H<sub>2</sub> and O<sub>2</sub> is still
a major challenging issue, which is vital for improving the efficiency
of overall water splitting. Herein, we employ a novel plasma-assisted
strategy to rapidly and conveniently synthesize the three-dimensional
(3D) porous composite nanosheets assembled on monodispersed Co nanoparticles
encapsulated in a carbon framework (CoNPs@C) on a carbon cloth. Such
a novel 3D hierarchical porous nanosheet improves the exposure and
accessibility of active sites as well as ensures high electroconductibility.
Moreover, the coating of a few graphene layers on the surface of catalysts
favors improvement of the catalytic activity. Benefited from these
multiple merits, the CoNPs@C composite nanosheets enable a low overpotential
of 153 mV at ā10 mA cm<sup>ā2</sup> for hydrogen evolution
reaction. Furthermore, they are also capable of catalyzing the oxygen
evolution reaction with high efficiency to achieve current density
of 10 mA cm<sup>ā2</sup> at the overpotential of 270 mV. Remarkably,
when assembled as an alkaline water electrolyzer, the bifunctional
CoNPs@C composite nanosheets can afford a water-splitting current
density of 10 mA cm<sup>ā2</sup> at a cell voltage of 1.65
V