Neslihan Yuca

Side-chain conducting and phase-separated polymeric binders for high-performance silicon anodes in lithium-ion batteries.

Here we describe a class of electric-conducting polymers that conduct electrons via the side chain π-π stacking. These polymers can be designed and synthesized with different chemical moieties to perform different functions, extremely suitable as a conductive polymer binder for lithium battery electrodes. A class of methacrylate polymers based on a polycyclic aromatic hydrocarbon side moiety, pyrene, was synthesized and applied as an electrode binder to fabricate a silicon (Si) electrode. The electron mobilities for PPy and PPyE are characterized as 1.9 × 10(-4) and 8.5 × 10(-4) cm(2) V(-1) s(-1), respectively. These electric conductive polymeric binders can maintain the electrode mechanical integrity and Si interface stability over a thousand cycles of charge and discharge. The as-assembled batteries exhibit a high capacity and excellent rate performance due to the self-assembled solid-state nanostructures of the conductive polymer binders. These pyrene-based methacrylate binders also enhance the stability of the solid electrolyte interphase (SEI) of a Si electrode over long-term cycling. The physical properties of this polymer are further tailored by incorporating ethylene oxide moieties at the side chains to enhance the adhesion and adjust swelling to improve the stability of the high loading Si electrode.

A systematic investigation of polymer binder flexibility on the electrode performance of lithium-ion batteries.

The mechanical failure at the electrode interfaces (laminate/current collector and binder/particle interfaces) leads to particle isolation and delamination, which has been regarded as one of the main reasons for the capacity decay and cell failure of lithium-ion batteries (LIBs). Polymer binder provides the key function for a good interface property and for maintaining the electrode integrity of LIBs. Triethylene glycol monomethyl ether (TEG) moieties were incorporated into polymethacrylic acid (PMAA) to different extents at the molecular level. Microscratch tests of the graphite electrodes based on these binders indicate that the electrode is more flexible with 5 or 10% TEG in the polymer binders. Crack generation is inhibited by the flexible TEG-containing binder, compared to that of the unmodified PMAA-based electrode, leading to the better cycling performance of the flexible electrode. With a 10% TEG moiety in the binder, the graphite half-cell reaches a reversible capacity of >270 mAh/g at the 1C rate, compared to a value of ∼190 mAh/g for the unmodified PMAA binder.

High capacity and high density functional conductive polymer and SiO anode for high-energy lithium-ion batteries.

High capacity and high density functional conductive polymer binder/SiO electrodes are fabricated and calendered to various porosities. The effect of calendering is investigated in the reduction of thickness and porosity, as well as the increase of density. SiO particle size remains unchanged after calendering. When compressed to an appropriate density, an improved cycling performance and increased energy density are shown compared to the uncalendered electrode and overcalendered electrode. The calendered electrode has a high-density of ∼1.2 g/cm(3). A high loading electrode with an areal capacity of ∼3.5 mAh/cm(2) at a C/10 rate is achieved using functional conductive polymer binder and simple and effective calendering method.

Synthesis of Carbon-Based Nano Materials for Hydrogen Storage

The aim of this study was to synthesize the carbon-based nanomaterials and determine their hydrogen storage capacities. Carbon nanotubes (CNTs) were first synthesized by chemical vapor deposition (CVD) of acetylene (C2H2) on a magnesium oxide (MgO) powder impregnated with an iron nitrate (Fe(NO3)3·9H2O) solution. The synthesis parameters were selected as the synthesis temperatures of 500 and 800°C, the iron content in the precursor of 5% and the synthesis time of 30 minutes. The synthesized material was purified by using HCl at 75°C for 15 hours. After synthesis of CNTs, the polyaniline-doped H3BO3 and BF3 and composites were prepared by coagulation method. The synthesized CNTs and composites were characterized by transmission electron microscopy, FT-IR spectroscopy, Raman spectroscopy and thermogravimetric analyzer. The BET specific surface areas were obtained from the nitrogen adsorption isotherms at -196°C. The hydrogen storage capacities of these carbonaceous materials were measured using volumetric method. It was found that the hydrogen adsorption capacities were changed in the range between 0.44 and 3.67wt% at the liquid nitrogen temperature and gas pressure up to 100 bar.

The role of H2 reduction in the growth of single-walled carbon nanotubes

Carbon nanotubes (CNTs) with their high mechanical, electrical, thermal and chemical properties are regarded as promising materials for many different potential applications. Chemical vapor deposition (CVD) is a common method for CNT synthesis especially for mass production. There are important parameters (synthesis temperature, catalyst and calcination conditions, substrate, carbon source, synthesis time, H2 reduction, etc.) affecting the structure, morphology and the amount of the CNT synthesis. In this study, CNTs were synthesized by CVD of acetylene (C2H2) on magnesium oxide (MgO) powder substrate impregnated by iron nitrate (Fe (NO3)3•9H2O) solution. The synthesis conditions were as follows: at catalyst calcination temperatures of 400 and 550°C, calcination time of 0, 15, 30 and 45 min, hydrogen concentrations of 0, 50 and 100 % vol, synthesis temperature of 800°C and synthesis time of 30 minutes. The synthesized materials were characterized by thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), X ray diffraction (XRD) and Raman spectroscopy. Effects of H2 reduction on catalyst calcination and CNT synthesis were investigated.

Different techniques for characterizing single-walled carbon nanotube purity

Transition-metal catalysts, fullerenes, graphitic carbon, amorphous carbon, and graphite flakes are the main impurities in carbon nanotubes. In this study, we demonstrate an easy and optimum method of cleaning SWCNTs and evaluating their purity. The purification method, which employed oxidative heat treatment followed by 6M HNO3, H2SO4, HNO3:H2SO4 and HCl acid reflux for 6h at 120°C and microwave digestion with 1.5M HNO3 for 0.5h at 210°C which was straightforward, inexpensive, and fairly effective. The purified materials were characterized by thermogravimetric analysis and nuclear techniques such as INAA, XRF and XRD.

Carbon nanotube synthesis with different support materials and catalysts

Having remarkable characteristics, carbon nanotubes (CNTs) have attracted a lot of interest. Their mechanical, electrical, thermal and chemical properties make CNTs suitable for several applications such as electronic devices, hydrogen storage, textile, drug delivery etc. CNTs have been synthesized by various methods, such as arc discharge, laser ablation and catalytic chemical vapor deposition (CCVD). In comparison with the other techniques, CCVD is widely used as it offers a promising route for mass production. High capability of decomposing hydrocarbon formation is desired for the selected catalysts. Therefore, transition metals which are in the nanometer scale are the most effective catalysts. The common transition metals that are being used are Fe, Co, Ni and their binary alloys. The impregnation of the catalysts over the support material has a crucial importance for the CNT production. In this study, the influence of the support materials on the catalytic activity of metals was investigated. CNTs have been synthesized over alumina (Al2O3), silica (SiO2) and magnesium oxide (MgO) supported Fe, Co, Fe-Co catalysts. Catalyst – support material combinations have been investigated and optimum values for each were compared. Single walled carbon nanotubes (SWCNTs) were produced at 800°C. The duration of synthesis was 30 minutes for all support materials. The synthesized materials were characterized by thermal gravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy.