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[en] Composite materials of molybdenum carbide and porous carbon were synthesised from molybdenum carbide using high temperature chlorination method with different applied chlorination times in order to use them as catalyst supports and electrode materials in various devices. X-ray diffraction, Raman spectroscopy, low temperature N2 sorption and high resolution transmission electron microscopy methods were used to characterise the structure of synthesised materials. The microporous-mesoporous material particles consist of β-Mo2C surrounded by porous amorphous carbon material. The partially chlorinated Mo2C particles were not surrounded by a graphitised shell. The specific surface area of the powders increased from 180 m2 g−1 up to 2020 m2 g−1 with increasing chlorination depth, i.e. decreasing carbon content in the particles. The stability and electrochemical behaviour of the synthesised composite materials were studied in 0.5 M H2SO4 solution using cyclic voltammetry and electrochemical impedance spectroscopy. The Mo2C phase in the studied composite materials was not stable in the acidic solution and dissolution of Mo2C was observed. The electrochemically treated working materials from which the Mo2C phase had been electrochemically dissolved had very good stability. The gravimetric capacitance increased with the increase of specific surface area and reached values up to 140 F g−1.
[en] Highlights: • MnO2-SiO2 composite film is prepared by potentiodynamical deposition. • Hierarchical porous MnO2 films is obtained after the etching of SiO2. • The obtained MnO2 film electrode exhibit high specific capacitance. - Abstract: We report a novel silica co-electrodeposition route to prepare nanostructured MnO2 films. Firstly, MnO2-SiO2 composite film was fabricated on a stainless steel substrate by potentiodynamical deposition, i.e. cyclic deposition, and then the SiO2 template was removed by simple immersion in concentrated alkaline solution, leading to the formation of a porous MnO2 (po-MnO2) matrix. The structure and morphology of the obtained films were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical properties of the po-MnO2 film were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS). Results showed that this porous MnO2 derived from the MnO2-SiO2 composite film exhibits good electrochemical performance for potential use as a supercapacitor material.
[en] SnO2 is a well-studied anode material for lithium ion batteries (LIBs). However, it undergoes severe capacity fading because of a large volume change (∼300%) during cycling. Composites of SnO2 with electro-conductive graphene would deliver improved capacity and rate performance. Nevertheless, achieving the theoretical capacity of SnO2 is still elusive, mainly because of disintegration of the active material from graphene and severe aggregation of SnO2, or Sn nanoparticles produced upon cycling. To surmount these limitations, in this work, nanocomposites containing ultra-fine sized SnO2 nanoparticles (UFSN) with reduced graphene oxide and amorphous carbon were synthesized in a single step at low temperature and environmentally benign way, in which ascorbic acid was employed as the carbon source and reducing agent. UFSN could decrease the lithium ion diffusion path length. As a result of effective buffering effect afforded by the mesoporous structure against volume change and improved lithium ion diffusivity, the ternary nanocomposite achieves ultra-high capacity of 1245 mAh g−1 after 210 cycles at 100 mA g−1 and excellent cycling stability. Since the proposed approach is facile, straightforward, and highly reproducible, it is anticipated that this system would be a potential alternative to the conventional graphite anode for LIBs.
[en] A flexible and free-collector-current of silicon-based anode is facilely prepared just by coating carbon black (CB) and silicon powders layer-by-layer. The resultant electrodes with a “sandwich” structure (CB/Si/CB) are assembled into half-cell and its electrochemical properties are tested. This type of anode exhibits excellent cycling and outstanding rate capability. The superior electrochemical performances are ascribed to both flexible CB-layers to offset the volume expansion of Si-particle. And, the CB-layer with high electric conductivity can provide efficient electron conductive pathways when Si particles react with lithium. More importantly, the CB/Si/CB electrodes without the collerctor (copper-foil) are exhibited high energy density, due to the weight proportion of copper foil is exceeded 60%. The CB/Si/CB electrode is used to assemble full-cell with the same structure as free-collector LCO/CB cathode material. It imposes the energy density of 200 Wh kg−1, and can keep stable charging-discharging capability at various deformations of shapes. And the flexible-cell of high performance is obtained to meet diverse applications in energy storage devices. Until now, many flexible batteries are put forward by researchers, but these product is faced with the complex production-process, high-cost material, low energy-density. This CB/Si/CB structure is produced with the matching current manufacturing industry and the common raw material, and to get a full-cell of the high energy density.
[en] Graphical abstract: Ultrafine cobalt sulfide nanoparticles encapsulated in hierarchical N-doped carbon nanotubes show exceptional lithium ion storage as anodes. - Abstract: Nanostructured cobalt sulfide based materials with rational design are attractive for high-performance lithium-ion batteries. In this work, we report a multistep method to synthesize ultrafine cobalt sulfide nanoparticles encapsulated in hierarchical N-doped carbon nanotubes (CoSx@HNCNTs). Co-based zeolitic imidazolate framework (ZIF-67) nanotubes are obtained from the reaction between electrospun polyacrylonitrile/cobalt acetate and 2-methylimidazole, followed by the dissolution of template. Next, a combined calcination and sulfidation process is employed to convert the ZIF-67 nanotubes to CoSx@HNCNTs. Benefited from the compositional and structural features, the as-prepared nanostructured hybrid materials deliver superior lithium storage properties with high capacity of 1200 mAh g−1 at 0.25 A g−1. More importantly, a remarkable capacity of 1086 mAh g−1 can be maintained after 100 cycles at the current density of 0.5 A g−1. Even at a high rate of 5 A g−1, a reversible capacity of 592 mAh g−1 after 1600 cycles can still be achieved.
[en] Highlights: • Amorphous ZnSnO3 double-shell hollow microcubes were synthesized. • D-ZnSnO3 deliver better electrochemical properties than Y-ZnSnO3. • The amorphous feature and double-shell hollow structure improves the performance. - Abstract: Amorphous ZnSnO3 double-shell and yolk-shell hollow microcubes were synthesized by calcination of their corresponding ZnSn(OH)6 precursors pre-prepared through a facile chemical solution method in argon. The as-prepared amorphous ZnSnO3 double-shell hollow microcubes have an average edge length of 1.6 μm. When used as the anode materials, amorphous ZnSnO3 double-shell hollow microcubes (D-ZnSnO3) reveal better electrochemical properties than ZnSnO3 yolk-shell counterparts (Y-ZnSnO3). D-ZnSnO3 anodes can retain a high reversible capacity of 741 mA h g−1 after 50 cycles with a coulombic efficiency of 99% at 100 mA g−1. The amorphous feature and unique box-in-box hollow architecture of D-ZnSnO3 play a key role in their excellent electrochemical properties.
[en] Highlights: • Self-supported Fe3O4/Ni/C electrode is prepared by a hydrothermal route. • The electrode presents nanoplate array structure with a 3D conductive network. • A high capacity of 832.5 mAh g−1 and an excellent rate-capability are delivered. - Abstract: An open-up network structure assembled by interconnected 3D heterostructure Fe3O4/Ni/C nanoplate arrays on Ni foam is successfully synthesized via a facile hydrothermal method with subsequent CVD heat treatment. When used as a binder free anode material for lithium-ion battery (LIBs), it shows quite a favorable electrochemical performance with high reversible capacity and good rate capability. A high capacity of 832.5 mAh g−1 is achieved at 0.3C and a specific capacity of 279 mAh g−1 can still be delivered at current density of 4.5C, corresponding to 34% of the capacity at 0.3C. The self-supporting nanoplates are intercrossed and interconnected with robust adhesion on Ni foam, preventing the active material from peeling off during the electrochemical reactions. Ni foam substrate, uniform carbon layer on the nanoplate surface and in-situ formed Ni nanocrystals together play important roles in effectively building a fast 3D electron transport network for electrode reactions. The excellent electrochemical performance makes this composite a promising candidate as anode material for high energy density LIBs.
[en] Highlights: • MnO2@N-dopedcarbonnanotube(N-CNT) composites are prepared by a facile process. • MnO2@N-CNT anodes exhibit better electrochemical properties than MnO2@CNT. • MnO2@N-CNT anodes show a capacity of 1415 mAh g−1 at 100 mA g−1 after 150 cycles. - Abstract: Carbon nanotube (CNT) has been widely applied to transition metal oxides anodes for lithium ion batteries, acting as a buffer, hollow backbone and conductive additive. Since the presence of N in carbon materials can enhance the reactivity and electrical conductivity, N-doped carbon nanotube (N-CNT) might be a better choice than pure CNT, which is exemplified by coaxial manganese dioxide@N-doped carbon nanotubes as a superior anode. The electrochemical properties of MnO2@N-CNT are investigated in terms of cycling stability and rate capability. The nanocomposite can deliver a specific capacity of 1415 mAh g−1 after 100 cycles at the current density of 100 mA g−1, which is better than that of MnO2@commercial CNT and MnO2. The excellent performance might be related to the integration of hollow structure, one-dimensional nanoscale size as well as combination with N-doped carbon materials.
[en] The Seebeck coefficient is reported for thermoelectric cells with gas electrodes and a molten electrolyte of one salt, lithium carbonate, at an average temperature of 750 °C. We show that the coefficient, which is 0.88 mV K−1, can be further increased by adding an inorganic oxide powder to the electrolyte. We interpret the measurements using the theory of irreversible thermodynamics and find that the increase in the Seebeck coefficient is due to a reduction in the transported entropy of the carbonate ion when adding solid particles to the alkali carbonate. Oxides of magnesium, cerium and lithium aluminate lead to a reduction in the transported entropy from 232 ± 12 to around 200 ± 4 J K−1 mol−1. This is of importance for design of thermoelectric converters.
[en] A potential positive electrode material, α-NaFeO2, can be viewed one of the base material for rechargeable Na batteries. In this study, we found that its structural evolution during charge process differentiates depending on its synthesis route. The α-NaFeO2 is prepared by three methods: one is by the hydrothermal technique (HT), and the other two by solid-state reactions, SSn and SSμ, in which nano-sized Fe3O4 and micro-sized Fe3O4 are used as the Fe source, respectively. The synchrotron radiation X-ray diffraction profiles of the initial state suggest that all three samples are apparently identified as the target product, α-NaFeO2, with rhombohedral structures. Though all three samples remain stable for more than 50 cycles under the cycling conditions of a constant amount of charging (Na extraction) to 70 mA h g−1, their structural evolution differs during the sodium extraction. The SSμ transitions from the rhombohedral structure to a spinel-like cubic structure, while the HT transforms into a monoclinic structure. On the other hand, both the monoclinic and cubic phases co-exist in SSn. What produces these differences among the seemingly identical materials is discussed.