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

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    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>ā€“1</sup> at 10 C), and long cycling life (over 77% capacity retention after 10ā€Æ000 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>ā€“1</sup> at a power density of 39 W kg<sup>ā€“1</sup>. Even at a high current rate of 5 A g<sup>ā€“1</sup> (corresponds to finish a full charge/discharge process in 2 min), the SIC still works well after 20ā€Æ000 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

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    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>ā€“1</sup> at a current density of 1 A g<sup>ā€“1</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

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    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 āˆ¼20 Ī¼m length with a diameter of 80ā€“100 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

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    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>ā€“1</sup>, with nearly no capacity loss in 90 cycles. Rate performance shows that even at the high current density of 13 A g<sup>ā€“1</sup>, the anode could still deliver a higher capacity than that of graphite

    Flexible Transparent and Free-Standing Silicon Nanowires Paper

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    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 siliconā€™s 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 āˆ¼10 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

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    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 chargeā€“discharge occurred with a current density of 0.5 A g<sup>ā€“1</sup>, the electrodes exhibit a high reversible capacity (760 mA h g<sup>ā€“1</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 lithiumā€“copper iron sulfide battery and lithiumā€“sulfur 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

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    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 āˆ¼5 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>ā€“1</sup> after 150 cycles)

    Amorphous ZnO Quantum Dot/Mesoporous Carbon Bubble Composites for a High-Performance Lithium-Ion Battery Anode

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    Due to its high theoretical capacity (978 mA h g<sup>ā€“1</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>ā€“1</sup> (at current density of 100 mA g<sup>ā€“1</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

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    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 āˆ¼50 layers experience an interesting splitting process that was driven by electrolyte diffusion, which occurs before the Geā€“Li alloying plateau begins. Two types of different splitting mechanism addressed as ā€œinside-outā€/zipper effect and ā€œoutside-inā€ dominate this process, which are resulted from the SEI layer growing longitudinally along the Geā€“graphite 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 nanowiresā€“thin 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 Geā€“C 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

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    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 āˆ’10 mA cm<sup>ā€“2</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>ā€“2</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>ā€“2</sup> at a cell voltage of 1.65 V
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