ABSTRACT
Transition-metal sulfides have been extensively studied as anode materials for use in sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to their multi-electron reactions, high rate performance, and abundant available resources. However, the practical capacities of metal sulfides remain low due to conductivity issues, volume expansion, and the use of traditional carbonate electrolytes. To overcome these drawbacks, ether electrolytes can be combined with nanoparticle-based metal sulfide anodes. Herein, a nanoparticle-based nickel monosulfide (NiS) anode with high rate performance in the ether electrolytes of SIBs/PIBs was prepared by heating a mixture of nickel nanoparticles with sulfur. In SIBs, the NiS anode capacity was 286 mA h g-1 at a high current density of 100 A g-1, and excellent cycling performance was observed at 25 A g-1 with a capacity of 468 mA h g-1 after 1000 cycles. Moreover, a full-cell containing a Na3V2(PO4) cathode demonstrated a rate performance of 65 mA h g-1 at a high current density of 100 A g-1. In PIBs, the NiS electrode capacity was 642 and 37 mA h g-1 at 0.5 and 100 A g-1, respectively. Hence, the synthesised NiS nanoparticles possessed excellent storage capability, regardless of the alkali-ion type, suggesting their potential use as robust NiS anodes for advanced battery systems.
ABSTRACT
In this study, NiS/graphene nanocomposites were synthesized by simple heat treatment method of three graphene materials (graphene oxide (GO), reduced graphene oxide (rGO) and nitrogen-doped graphene oxide (N-rGO)) and NiS precursor. The morphology and crystal structure of NiS/graphene nanocomposites were characterized using field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Electrochemical properties were also investigated. NiS/graphene nanocomposites homogeneously wrapped by graphene materials have been successfully manufactured. Among the three nanocomposites, NiS/N-rGO nanocomposite exhibited the highest initial and retention capacity in discharge, respectively, of 1240 mAh/g and 467 mAh/g up to 100 cycles at 0.5 C.
ABSTRACT
Polyacrylonitrile (PAN)/Si composite fibers (electrodes) with flexibility were fabricated using an elec-trospinning method and then Si-embedded carbon (Si/C) fibers were prepared by carbonizing the composite fibers at 800, 900, and 1000°C. Si particles were distributed in the interior and exterior of entangled PAN fibers. After carbonization, the structure of electrodes was preserved but the diameter of fibers was decreased owing to the release of component elements constituting PAN such as nitrogen and oxygen. Crystalline Si particles existed in carbon fibers with both amorphous and crystalline phases. As carbonization temperature increased, the carbon content and the crys-tallinity of carbon increased. The electrode carbonized at 1000°C with the lowest charge transfer resistance exhibited the best electrochemical properties in terms of capacity, coulombic efficiency and cycle life.
ABSTRACT
In this work, bare Sn and carbon-coated Sn nanoparticles were prepared by a pulsed wire evaporation process. The effect of binder and pressing ratio on electrochemical properties of Sn/C composite electrodes was investigated to enhance the structural stability of Sn anode. The electrode containing the polyamide-imide (PAI) binder with high tensile strength (52 MPa) exhibited higher coulombic efficiency and better cycle performance compared to the electrode with the conventional polyvinylidene fluoride (PVdF) binder. The 5%-pressed Sn/C electrode with the proper porosity in the electrode demonstrated the best cycle performance corresponding to 45% of capacity retention ratio until 100 cycles.
ABSTRACT
Owing to the speculated price hike and scarcity of lithium resources, sodium-ion batteries are attracting significant research interest these days. However, sodium-ion battery anodes do not deliver good electrochemical performance, particularly rate performance. Herein, we report the facile electrospinning synthesis of a free-standing nickel disulfide (NiS²) embedded on carbon nanofiber. This electrode did not require a conducting agent, current collector, and binder, and typically delivered high capacity and rate performance. The electrode delivered a high initial capacity of 603 mAh g-1 at the current density of 500 mA g-1. Moreover, the electrode delivered the capacity of 271 mAh g-1 at the high current density of 15 A g-1. The excellent rate performance and high coulombic efficiency of the electrode were attributed to its low charge transfer resistance and unique structure.
ABSTRACT
Sodium-ion batteries (SIBs) are a viable substitute for lithium-ion batteries due to the low cost and wide availability of sodium. However, practical applications require the development of fast charging sodium-ion-based full-cells with high power densities. Na3V2(PO4)3 (NVP) is a bipolar material with excellent characteristics as both a cathode and an anode material in SIBs. Designing symmetric cells with NVP results in a single voltage plateau with significant specific capacity which is ideal for a full cell. Here we demonstrate for the first time a tremendous improvement in the performance of NVP symmetric full cells by introducing an ether-based electrolyte which favors fast reaction kinetics. In a symmetric full cell configuration, 75.5% of the initial capacity was retained even after 4000 cycles at 2 A g-1, revealing ultra-long cyclability. Excellent rate performances were obtained at current densities as high as 1000C, based on the cathode mass, revealing ultrafast Na+ transfer. The power density obtained for this NVP symmetric cell (48 250 W kg-1) is the best among those of all the sodium-ion-based full cells reported to date.
ABSTRACT
Tin monoxide (SnO) anodes are promising candidates for use in sodium-ion batteries because of their high theoretical capacities and stable cycle performance. In previous reports, electrodes with excellent performance have been prepared by using nano-sized SnO particles. However, the synthesis of nano-sized SnO particles is complex, time-consuming, and expensive. In this paper, an anode of micron-sized SnO is prepared by using commercial micron-sized SnO particles. The electrode exhibits a reversible capacity of 450 mAh g-1 in the 1st cycle at a current rate of 100 mA g-1. We used a tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte, which is well known for its superior electrochemical performance in sodium-ion batteries. The mechanism of operation of the anode containing micron-sized SnO particles has been confirmed by a detailed study using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). During initial discharge, the SnO changed to Sn and sodium oxide, and the surface of the electrode became covered with a film. The electrode composed of micron-sized SnO is a potential candidate for use in sodium-ion batteries.
ABSTRACT
Ball-milling process was applied to increase sulfur content in sulfur/polyacrylonitrile (SPAN) composites and improve electrochemical properties of Li/S batteries. In contrast to as-received PAN, pre-heated PAN was pulverized by the ball-milling, resulting in the continuous size reduction with increasing the milling time. Sulfur contents in SPAN composites synthesized with a pre-heated and milled PAN were increased with prolonging the milling time and the maximum content reached 44.5% for the milling time of 10 h. Li/S cells with SPAN electrodes delivered the first discharge capacities of 1356, 1409, 1512, and 1610 mAh/g-sulfur for milling times of 0, 1, 5, and 10 h. The 10 h-milled SPAN electrode with the highest sulfur content exhibited poor initial efficiency and low capacity retention at 100 cycles, whereas from a comprehensive viewpoint of the specific capacity and capacity retention, the 6 h-milled SPAN electrode exhibited the best electrochemical performance due to the suitable size and sulfur content.
ABSTRACT
Si film electrodes were deposited onto Cu foil current collectors fabricated with well-formed CuO nanostructures. The structural and electrochemical properties of the Cu foils oxidized for 1, 3, and 6 h and of the Si film electrodes were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), and charge/discharge tests. The morphologies and XRD profiles suggested that the oxidized Cu foils consisted of a top CuO layer and a bottom Cu2O layer. The surface roughness of the Cu foils decreased with increasing oxidation time since the flower-like CuO nanostructures weakly adhered to the surface were easily detached by ultrasonic cleaning. The cycle performance of the Si film electrode with the rougher CuO layer rapidly deteriorated, whereas the flat Cu2O layer showing a relatively high electric conductivity induced the formation of a dense Si film and improved the electrochemical performance of the Si film electrode.
ABSTRACT
Bare and ZrO2-coated LiCoO2 thin films were fabricated by direct current magnetron sputtering method on STS304 substrates. Deposited both films have a well-crystallized structure with (003) preferred orientation after annealing at 600 degrees C. The ZrO2-coated LiCoO2 thin film provide significantly improved cycling stability compared to bare LiCoO2 thin film at high cut-off potential (3.0-4.5 V). The improvement in electrochemical stability is attributed to the structural stability by ZrO2 coating layer.
ABSTRACT
LiCoO2 thin films were fabricated by direct current magnetron sputtering method on STS304 and Ti substrates. The effects of substrate and annealing on their structural and electrochemical properties of LiCoO2 thin film cathode were studied. Crystal structures and surface morphologies of the deposited films were investigated by X-ray diffraction and field emission scanning electron microscopy. The as-deposited films on both substrates have amorphous structure. The (104) oriented perfect crystallization was obtained by annealing over 600 degrees C in STS304 substrate. The LiCoO2 thin film deposited on Ti substrate shows the (003) texture after annealing at 700 degrees C. The electrochemical properties were investigated by the cyclic voltammetry and charge-discharge measurement. The 600 degrees C-annealed LiCoO2 film deposited on STS304 substrate exhibits the inithial discharge capacity of 22 uAh/cm2 and the 96% capacity retention rate at 50th cycles. The electrochemical measurement on annealed films over 600 degrees C was impossible due to the formed TiO2 insulator layer using Ti substrate. As a result, it was found that the STS304 substrate seems to be more suitable material than the Ti substrate in fabricating LiCoO2 thin film cathode.
ABSTRACT
Si and Si/Ti films were fabricated on a Cu current collector (substrate) using the DC sputtering system. The Ti film as a buffer layer was inserted between the Si film and the Cu current collector. Their structural and electrochemical properties were investigated with various Ti film thicknesses of 20-90 nm. The Si and Ti films deposited on a polycrystalline Cu substrate were amorphous. The Si/Ti/Cu film electrode exhibited better electrochemical properties than the Si/Cu electrode in terms of capacity, charge-discharge efficiency, and cycleability. In the Si/Ti/Cu electrode, the film electrode with a 55 nm Ti film thickness showed the best electrochemical properties: 367 microA h/cm2 initial capacity, 91% efficiency, and 50% capacity retention after 100 cycles. These good electrochemical properties are attributed to the enhanced adhesion between the Si and Ti films. Additionally, the modified surface morphology of Si film with a cluster structure could withstand the lateral volume change during the charge-discharge process.
ABSTRACT
A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode.
ABSTRACT
We have successfully synthesized beta-Ga2O3 nanomaterials with various morphologies, such as wire, rod, belt and sheet-like, through simple thermal evaporation of metal gallium powder in the presence of nickel oxide catalyst. beta-Ga2O3 nanomaterials with different morphology were observed as a function of synthesis time and temperature. In this report, generation sites of the beta-Ga2O3 nanomaterials have been delicately surveyed by FESEM. The growth mechanisms of nanomaterials are distinguished by the view of its generation site. The growth of nanowire follows both VLS and VS mechanism and other kinds of materials such as nanorod, nanobelt and nanosheet follows VS mechanism.
ABSTRACT
Nanostructured Ti-Ni alloys were prepared by cold working followed by annealing, and then their shape memory characteristics and superelasticity were investigated by means of differential scanning calorimetry (DSC), transmission electron microscopy (TEM), thermal cycling tests under constant load and tensile tests. Morphology of amorphous phases induced by cold working depended largely on the amount of cold working. They had domain like shape in the 40% cold rolled alloy, while had mainly wide band shape in the 70% cold rolled alloy. In 40% cold rolled alloy, the average grain size increased from 27 nm to 80 nm with increasing annealing temperature from 573 K to 673 K. Transformation elongation increases with raising annealing temperature, which was ascribed to the increase in grain size reducing the constraints of grain boundaries. Transformation hysteresis increased rapidly with raising annealing temperature up to 623 K, above which they almost keep constant, which was ascribed to the small grain size and large constraints of grain boundaries.
