Amorphous carbon-coated silicon nanocomposites: a low-temperature synthesis via spray pyrolysis and their application as high-capacity anodes for lithium-ion batteries

This article introduces an effective, inexpensive, and industrially oriented approach to produce carbon-coated Si nanocomposites as high-capacity anode materials for use in rechargeable lithium-ion batteries. Initially, nanosized Si particles (nm) were mixed in a citric acid/ethanol solution via ultrasonication. This mixture was further spray-pyrolyzed in air at low processing temperature (300-500 C), resulting in a homogeneous layer of carbon coating on the surface of the spheroidal Si nanoparticles. The effects of the processing temperature on the amorphous carbon content, the thickness of the carbon-coating layer, and the homogeneity of the carbon coating were studied in detail. These parameters strongly influenced the electrochemical performance of the carbon-coated Si nanocomposites, as will be discussed below. Carbon-coated Si nanocomposites spray-pyrolyzed in air at 400 C show the best cycling performance, retaining a specific capacity of 1120 mA·h g-1 beyond 100 cycles, with a capacity fading of less than 0.4% per cycle. The beneficial effect of the carbon coating in enhancing the dimensional stability of the Si nanoparticles appears to be the main reason for this markedly improved electrochemical performance

Nanostructured materials for electrodes in lithium-ion batteries

The commercially available lithium-ion cells, which are the most advanced among the rechargeable battery systems available so far, employ polycrystalline microsized powder as the electrode materials, which functions as the Li-ion insertion hosts. With the advancement of nanotechnology, there is an interest in the replacement of conventional materials by nanostructured materials. The use of nanoparticles in composite electrodes for Li-ion batteries may have considerable kinetic advantages due to the reduction of the diffusion length for lithium-ion insertion into the active mass, and also because of the reduction of the overall charge transfer resistance of the electrodes. In this doctoral work, several nanostructured materials were examined and characterized for possible application as electrode materials in Li-ion rechargeable batteries. Among the anode candidates studied were free-standing single-walled carbon nanotube (SWCNT) paper, lead oxide (PbO) and lead oxide-carbon (PbO-C) nanocomposite, and carbon-coated silicon (Si-C) nanocomposite materials. Meanwhile, several cathode candidates were also studied: nanostructured vanadium oxide (V2O5), lithium trivanadate (LiV3O8) nanoparticles, and lithium manganese oxide (LiMn2O4) thin film electrode. Free-standing SWCNT paper electrodes have been synthesized by a simple filtration method via positive pressure. The free-standing electrode was produced without any binder or metal substrate, which reduced the weight significantly. The free-standing SWCNT paper electrodes were also flexible and had good electrical conductivity. With the addition of both carbon black and nanosized Si particles, the electrical conductivity and specific capacity of the free-standing SWCNT paper electrode were greatly enhanced, so that they retained a capacity of 400 mAh g-1 beyond 100 cycles. A new approach has been used to prepare nanostructured PbO and PbO-C composites via the spray pyrolysis technique. The prepared powders consist of fine nanocrystalline PbO homogeneously distributed within an amorphous carbon matrix with highly developed surface area. The combination of spray technology and carbon addition increased the specific surface area (above 6 m2 g-1) and the conductivity of PbO, and also improved the specific capacity, with a reversible capacity above 100 mAh g-1 retained beyond 50 cycles. An effective, inexpensive, and industrially oriented approach was applied to produce carbon-coated Si nanocomposites. Carbon-coated Si nanocomposites spraypyrolyzed in air at 400 oC showed the best cycling performance, retaining a specific capacity of 1120 mAh g-1 beyond 100 cycles, with a capacity fading of less than 0.4 % per cycle. The beneficial effect of the carbon-coating in enhancing the dimensional stability of the Si nanoparticles appears to be the main reason for this markedly improved electrochemical performance. One-dimensional (1D) nanostructures of V2O5 have been successfully synthesized via a precipitation process followed by heating in vacuum at 300 oC. The increase in crystallinity and higher yield of one-dimensional nanostructured oxides contributed significantly to the improved capacity and enhanced cycle life. V2O5 nanoparticles were also synthesized via the flame spray pyrolysis (FSP) process in air. They showed an improved cycle life when the cut-off potential for discharging was increased from 1.5 Vto 2.5 V. The significant capacity loss when discharging to 1.5 V is possibly related to the dissolution of vanadium active mass and the structural changes upon cycling in the larger potential span. The flame spray pyrolyzed V2O5 nanoparticles show excellent cyclability when cycled between 2.5 V and 4.0 V vs. Li/Li+, retaining a discharge capacity of 120 mAh g-1 beyond 100 cycles at a cycling rate of 100 mA g-1. LiV3O8 nanoparticles (~24 nm in size) have been synthesized by FSP for the first time. The assynthesized LiV3O8 nanoparticles proved to be a promising cathode material for lithium rechargeable batteries, retaining a specific discharge capacity of 180 mAh g-1 beyond 50 cycles. A series of LiMn2O4 thin films on either Si (100) or stainless steel substrate were successfully prepared via pulsed laser deposition (PLD). The as-deposited LiMn2O4 thin films on stainless steel substrate are highly lithium- and oxygen-deficient, as confirmed by ERDA/RBS and Raman analysis. Lithium and oxygen content increased when the pulse rate was increased, leading to thicker films. However, the LiMn2O4 thin film with the lowest deposition pulse rate (or thinnest film) exhibited the best electrochemical performance, retaining a charge capacity of 48 μAh cm-2 μm-1 beyond 100 cycles

Dehydration of ethanol-water mixture by vapor permeation through hollow fiber membranes

Master'sMASTER OF ENGINEERIN

Low-temperature synthesis of polypyrrole-coated LiV3O8 composite with enhanced electrochemical properties

A composite, LiV3O8 -polypyrrole (PPy), was synthesized by a low-temperature solution route followed by an in situ polymerization method. The as-prepared powders consisted of nanosized PPy distributed homogeneously within the layered lithium trivanadate. The electrochemical properties of LiV3O8–PPy composite were systematically investigated and compared with bare lithium trivanadate. It was found that the electrochemical performance of the LiV3O8–PPy composite was significantly enhanced, with a specific capacity of ∼183mAhg−1 retained after 100cycles . This suggests that nanostructured PPy could work well as a polymer-conducting matrix and also as a binding material to improve the overall electrochemical properties of the LiV3O8 when used as a cathode material in lithium-ion batteries

Electrochemistry of LiV3O8 nanoparticles made by flame spray pyrolysis

LiV3O8 nanoparticles (primary particles with ca. 50 nm diameter) have been synthesized by flame spray pyrolysis (FSP). The powder was characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and galvanostatic cycling. The initial discharge capacity of the LiV3O8 nanoparticles is 271 mAh g-1 when discharged from its open-circuit potential to 2.0 V vs Li/Li+ at a specific current of 100 mA g-1 under ambient conditions. The nanoparticles retained a specific discharge capacity of 180 mAh g-1 beyond 50 cycles. This paper describes the synthesis route as well as the characterizations of the FSP-produced LiV3O8 nanoparticles

Obesogenic television food advertising to children in Malaysia: sociocultural variations

Background: Food advertising on television (TV) is well known to influence children’s purchasing requests and models negative food habits in Western countries. Advertising of unhealthy foods is a contributor to the obesogenic environment that is a key driver of rising rates of childhood obesity. Children in developing countries are more at risk of being targeted by such advertising, as there is a huge potential for market growth of unhealthy foods concomitant with poor regulatory infrastructure. Further, in developing countries with multi-ethnic societies, information is scarce on the nature of TV advertising targeting children. Objectives: To measure exposure and power of TV food marketing to children on popular multi-ethnic TV stations in Malaysia. Design: Ethnic-specific popular TV channels were identified using industry data. TV transmissions were recorded for each channel from November 2012 to August 2013 (16 hr/day) for randomly selected weekdays and weekend days during normal days and repeated during school holidays (n=88 days). Coded food/beverage advertisements were grouped into core (healthy), non-core (non-healthy), or miscellaneous (unclassified) food categories. Peak viewing time (PVT) and persuasive marketing techniques were identified. Results: Non-core foods were predominant in TV food advertising, and rates were greater during school holidays compared to normal days (3.51 vs 1.93 food ads/hr/channel, p\u3c0.001). During normal days’ PVT, the ratio of non-core to core food advertising was higher (3.25 food ads/hr/channel), and this more than trebled during school holidays to 10.25 food ads/hr/channel. Popular channels for Indian children had the lowest rate of food advertising relative to other ethnic groups. However, sugary drinks remained a popular non-core product advertised across all broadcast periods and channels. Notably, promotional characters doubled for non-core foods during school holidays compared to normal days (1.91 vs 0.93 food ads/hr/channel, p\u3c0.001). Conclusions: This study highlights non-core food advertising, and predominantly sugary drinks are commonly screened on Malaysian TV channels. The majority of these sugary drinks were advertised by multinational companies, and this observation warrants regulatory attention

Flame spray-pyrolyzed vanadium oxide nanoparticles for lithium battery cathodes

Vanadium pentoxide (V2O5) nanoparticles (30–60 nm) were made by a one-step and scalable flame spray pyrolysis (FSP) process. Optimization of the FSP processing conditions (precursor concentration and injection rate) enhanced the electrochemical performance of these nanoparticles. Increasing the cut-off potential for discharging from 1.5 to 2.5 V vs. Li/Li+ improved the cycle life of these V2O5 nanoparticles. Particles with the lowest specific surface area (32 m2 g−1) and highest phase purity (up to 98 wt%) showed excellent cyclability between 2.5 and 4.0 V vs. Li/Li+, retaining a specific charge of 110 mAh g−1 beyond 100 cycles at a specific current of 100 mA g−1, and also superior specific charge of 100 mAh g−1 at specific current up to 20C rate (or 2000 mA g−1)

Foam-like, microstructural SnO2-carbon composite thin films synthesized via a polyol-assited thermal decomposition method

Foam-like, microstructural SnO2–carbon composite thin films were synthesized by refluxing SnCl2·2H2O in ethylene glycol (EG) at 195 °C for 4 h under vigorous stirring in air followed by thermal decomposition of the as-synthesized precursor solution, whereby the products were deposited onto stainless steel (SS) substrates. Subsequently, the decomposed product, which now consists only of the microstructural SnO2–carbon composite thin film, without the addition of any binder and carbon black conductive agent, was directly applied as an anode material for use in a Li-ion rechargeable battery. Physical and electrochemical characterizations of the as-synthesized thin films were carried out. The foam-like, microstructural SnO2–carbon composite thin films that undergo thermal decomposition in air at 300 °C demonstrated the best cyclability, delivering a specific discharge capacity of approximately 496 mAh g−1 beyond 100 cycles. We believe that the presence of a uniform, SnO2–carbon network throughout the foam-like thin film, acts not only as an improved conducting network but also buffered the volume expansion upon Li–Sn alloying, resulting in a much improved cycling of the composite thin film electrode