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

Advanced materials for electrodes and electrolyte in rechargeable lithium batteries

The lithium-ion (Li-ion) battery possesses many outstanding advantages over the well known rechargeable battery systems, in particularly higher energy density and longer shelf life, as well as not suffering from the memory effect problems of Ni-MH batteries. Those advantages are making it the greatest energy source of choice for the portable electronic market. Graphite and LiCoO2 are commonly used in commercial Li-ion battery. Despite their widespread utilization, the current electro-active materials have reached to a limit in terms of delivering even higher power, energy density, and longer cycle life for the new, emerging field of large-scale energy storage systems, such as in the automotive industry. Hybrid and fully electric cars need safer, cheaper, and higher performing batteries in order to offer an important alternative to combustion engines. To overcome the shortcomings of the current Li-ion battery, improvements are needed to push the Li-ion technology to the next level. Hence, the motivation for this PhD work is to search for potential electro-active materials, by means of the synthesis of film and powder based electrodes, fine-tuning of the composition of the composite electrodes, and characterization of them for possible application in Li-ion rechargeable batteries. Among the anode candidates studied were free-standing carbon nanotube (CNT) films, tin glycolate, and polypyrrole coated silicon (Si-PPy) nanocomposite materials. Two cathode candidates were also studied: lithium manganese oxide (LiMn2O4) thin film, and polypyrrole coated lithium trivanadate (LiV3O8-PPy) composite. Ionic liquid based polymer electrolyte was also studied to enhance Li-ion battery safety features. Free-standing CNT film electrodes have been synthesized by a simple vacuum filtration method. The free-standing electrodes were produced without any binder or metal current collector, which significantly reduced the total weight. The free-standing CNT film electrodes were also flexible and had good electrical conductivity with the addition of carbon black. Three different types of CNTs were used, i.e. single-wall CNTs (SWCNTs), double-wall CNTs (DWCNTs) and multi-wall CNTs (MWCNTs). The films based on MWCNT are much better than SWCNT and DWCNT films in terms of their electrochemical performance, with stable cycling behavior of 300 mAh g-1 after 40 cycles. A detailed study revealed that MWCNT electrode exhibited a reversible, sharp, and intense peak at approximately 0.15 V vs. Li/Li+ during the Li+ de-intercalation process. A thin solid electrolyte interphase (SEI) layer was observed on the surface of MWCNTs after prolonged cycling. This proved that only multi-wall CNTs have the capability for significant Li+ ion intercalation/de-intercalation. Novel tin glycolate particles were prepared by the polyol-mediated method. The prepared powders consist of fine tin-based particles (80 – 120 nm), encapsulated within tin glycolate shells. When applied as an anode material for Li-ion batteries, the glycolate shells buffered the volume expansion upon Li-Sn alloying, and thus the tin glycolate particles showed a high specific charge of 416 mAh g-1 beyond 50 cycles. Novel Si-PPy nanocomposite was prepared by coating the Si particle surfaces with PPy by the in situ chemical polymerization method. The cycle stability of Si-PPy nanocomposite electrodes was greatly enhanced with 50 wt. % PPy. The loading level of PPy plays a major role in determining the stability of the nanocomposite, and consequently creates a good matrix to improve the electrical conductivity, buffer the volume change during cycling, and prevent cracking and pulverization of the Si. A new approach was developed to rapidly synthesize nanostructured LiMn2O4 thin films by flame spray deposition (FSD) and in situ annealing. The LiMn2O4 films on stainless steel current collector exhibited good cyclability, with two pairs of redox peaks at approximately 4.00 and 4.15 V vs. Li/Li+. The study indicated that spinel LiMn2O4 thin films can be prepared by the fast and efficient FSD method. LiV3O8-PPy composites were synthesized by a low-temperature solution route followed by an in situ polymerization method. For LiV3O8 material, only 24 wt. % of PPy is needed to enhance the electrical conductivity and stability of the composite electrode, which delivered a specific charge of 183 mAh g-1 beyond 100 cycles. A solution casting method was used to prepare IL-PE composite membrane. The composite membrane was then assembled with LiV3O8-PPy (24 wt. % PPy) composite cathode and tested as a lithium polymer battery at room temperature. The cell delivered 200 mAh g-1 with respect to the mass of the cathode material

The Effect Of Blending Acrylic Grafted Pvc And Pvc K-66 With Abs On Impact And Flexural Properties

Blends of acrylonitrile butadiene styrene (ABS) and poly(vinyl chloride) (PVC) were studied. The blends were prepared in different ratios by melt blending technique. High rigidity, medium impact and super high impact ABS were used as the base polymer. Acrylic grafted PVC and PVC K-66 were incorporated into the blends. Particular emphasis was on Izod impact test. The impact strength of the blends increased with increasing content of PVC. Interestingly, the result shows that the highest impact strength occurs when acrylic grafted PVC was added into super high impact ABS. However, it was observed that when PVC is incorporated in ABS, there is a decrease in the flexural modulus. The least decrease occurred when PVC K-66 was added into high rigidity ABS. These observations are consistent with the morphological studies. Scanning electron microscopy (SEM) revealed that an increase in PVC content results in greater ductility

Mechanical, chemical & flammability properties of ABS/PVC blends

The first completely synthetic plastic, phenol-formaldehyde, was introduced by Baekeland in 1909, nearly four decades after Hyatt had developed a semisynthetic plastic-cellulose nitrate (Chanda and Roy, 1993). In 1927 poly(vinyl chloride) (PVC) and cellulose acetate were developed, and 1929 saw the introduction of urea- formaldehyde (UF) resins (Chanda and Roy, 1993). The development of new polymeric materials proceeded at an even faster pace after the war. Epoxies were developed in 1947, and acrylonitrile-butad iene-styrene (ABS) terpolymer in 1948 (Chanda and Roy, 1993). The next two decades saw the commercial development of a number of highly temperature-resistance materials. More recently, other new polymer materials were introduced, including several exotic materials which are mostly very expensive

Mechanical and flammability properties of ABS/PVC blends

Blending of polymers is often used as a means to develop new materials with the desired properties. The main objective of this research is to study the effect of different PVC molecular weight (K-58 and K-66) and acrylic grafted PVC on different grades of ABS in terms of mechanical and flammability properties. Morphological, thermal and rheological properties of the blends were also investigated. Three grades of ABS were used; high rigidity, medium impact and super high impact. Using a single screw extruder, blends of ABSIPVC in various compositions ranging from 100 - 80% ABS were prepared and injection moulded. Interestingly, a synergist effect is observed whereby the impact strength of the ABSPVC blends is higher than the pure polymer. With increasing PVC content, the impact strength of the blends increased. The impact strength was also found to be dependant upon PVC molecular weight, with the higher K-value, the higher the impact strength. Acrylic grafted PVC is more effective in increasing the impact strength than the non grafted PVC. The impact strength enhancement increases with increasing rubber content in the ABS. The result also shows that the highest impact strength occurs when acrylic grafted PVC was added into super high impact ABS. However, it was observed that when PVC is incorporated in ABS, there is a marginal decrease in flexural modulus. The flexural modulus of the blends was also found to be dependant upon PVC molecular weight, with the lower K-value, the higher the flexural modulus. With increasing PVC content, the flexural modulus of the blends decreased. The highest flexural modulus among the blends is high rigidity ABSI PVC K-58. The DMA study confirmed that the SAN component of ABS is highly miscible with PVC. The miscibility between SAN component of ABS has improved the interfacial adhesion between PVC and ABS. The flammability of the blends determined by the LO1 test shows that the flammability of the blends decreased with increasing PVC content. The most optimum formulation in terms of cost and mechanical properties is 80 super high impact ABS/20 PVC K-66

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

Electrodeposition of MnO2 nanowires on carbon nanotube paper as free-standing, flexible electrode for supercapacitors

MnO2 nanowires were electrodeposited onto carbon nanotube (CNT) paper by a cyclic voltametric technique. The as-prepared MnO2 nanowire/CNT composite paper (MNCCP) can be used as a flexible electrode for electrochemical supercapacitors. Electrochemical measurements showed that the MNCCP electrode displayed specific capacitances as high as 167.5 F g-1 at a current density of 77 mA g-1. After 3000 cycles, the composite paper can retain more than 88% of initial capacitance, showing good cyclability. The CNT paper in the composite acted as a good conductive and active substrate for flexible electrodes in supercapacitors, and the nanowire structure of the MnO2 could facilitate the contact of the electrolyte with the active materials, and this increase the capacitance

Lithium-polymer battery based on an ionic liquid–polymer electrolyte composite for room temperature applications

A lithium-polymer battery based on an ionic liquid&ndash;polymer electrolyte (IL&ndash;PE) composite membrane operating at room temperature is described. Utilizing a polypyrrole coated LiV3O8 cathode material, the cell delivers &gt;200 mAh g&minus;1 with respect to the mass of the cathode material. Discharge capacity is slightly higher than those observed for this cathode material in standard aprotic electrolytes; it is thought that this is the result of a lower solubility of the LiV3O8 material in the IL&ndash;PE composite membrane.<br /

Nickel sulfide cathode in combination with an ionic liquid-based electrolyte for rechargeable lithium batteries

Nickel sulfides, pure Ni3S2 and a mixture of Ni7S6-NiS, were synthesized through a solvothermal process. The nickel sulphide powders were characterised by X-ray diffraction, scanning electron microscopy, and electrochemical testing. The results showed that the capacity of NiS-Ni7S6 is much higher than that of Ni3S2, when used as the cathode in a lithium cell with an organic solvent-based electrolyte, 1 M lithium bis (trifluoromethanesulfonyl)amide (LiNTf2) in poly(ethylene glycol) dimethyl either 500. The NiS-Ni7S6 electrodes were also tested with an ionic liquid electrolyte consisting of 1 M LiNTf2 in N-methyl-N-propyl pyrrolidinium bis(trifioromethanesulfonyl)amide ([C3mpyr][NTf2]) to compare with organic-solvent based electrolytes. The result revealed that the ionic liquid is a useful solvent for use with this cathode material

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