Elad Pollak - Academia.edu (original) (raw)

Papers by Elad Pollak

ECS Meeting Abstracts, 2011

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Electrolyte solutions for rechargeable Mg batteries were developed, based on reaction products of... more Electrolyte solutions for rechargeable Mg batteries were developed, based on reaction products of phenyl magnesium chloride ͑PhMgCl͒ Lewis base and AlCl 3 Lewis acid in ethers. The transmetallation of these ligands forms solutions with Mg x Cl y + and AlCl 4−n Ph n − ions as the major ionic species, as analyzed by multinuclei nuclear magnetic resonance spectroscopy. Tetrahydrofuran ͑THF͒ solutions of ͑PhMgCl͒ 2 -AlCl 3 exhibit optimal properties: highly reversible Mg deposition ͑100% cycling efficiency͒ with low overvoltage: Ͻ0.2 V and electrochemical windows wider than 3 V. A specific conductivity of 2-5 ϫ 10 −3 ⍀ −1 cm −1 could be measured between −10 and 30°C for these solutions, similar to that of standard electrolyte solutions for Li batteries. Mg ions intercalate reversibly with Chevrel phase ͑Mg x Mo 6 S 8 ͒ cathodes in these solutions. These systems exhibit high thermal stability. The solutions may enable the use of high voltage, high-capacity Mg insertion materials as cathodes and hence open the door for research and development of high-energy density, rechargeable Mg batteries.

Electrochemistry Communications, 2014

The electrochemical reactivity of polyimide-derived pyrolytic carbon film electrodes in a standar... more The electrochemical reactivity of polyimide-derived pyrolytic carbon film electrodes in a standard organic carbonate lithium-ion battery electrolyte was studied and quantified. An oxidative heat treatment at 900 o C under CO 2 atmosphere was found to lower the reactivity of disordered carbons towards electrolyte oxidation. Cyclic voltammetry and potentiostatic measurements of the carbon film electrodes demonstrate the beneficial effect of the CO 2 heat treatment in the potential range between 4.2 and 4.8 V vs. Li/Li + i.e., at potentials where high-energy Li-ion positive composite electrodes operate.

The Journal of Physical Chemistry C, 2007

... Elad Pollak,* Gregory Salitra, Valentina Baranchugov, and Doron Aurbach. Department of Chemis... more ... Elad Pollak,* Gregory Salitra, Valentina Baranchugov, and Doron Aurbach. Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel. J. Phys. Chem. ... 2) Baranchugov, V.;Markevich, E.; Pollak, E.; Salitra, G.; Aurbach, D. Electrochem. Commun.2007, 9, 796−800. ...

The Journal of Physical Chemistry B, 2006

The dependence of the electronic conductivity of activated carbon electrodes on their potential i... more The dependence of the electronic conductivity of activated carbon electrodes on their potential in electrolyte solutions was examined. Kapton polymer films underwent carbonization (1000°C), followed by a mild oxidation process (CO 2 at 900°C) for various periods of time, to obtain carbons of different pore structures. A specially designed cell was assembled in order to measure the conductivity of carbon electrodes at different potentials in solutions. When the carbon electrodes possessed molecular sieving properties, a remarkable dependence of their conductivity on their charging state was observed. Aqueous electrolyte solutions containing ions of different sizes were used in order to demonstrate this phenomenon. As the average pore size of the activated carbons was larger, their molecular sieving ability was lower, and the dependence of their conductivity on their charging state regained its classical form. This behavior is discussed herein.

Nano Letters, 2010

The interaction of Li + with single and few layer graphene is reported. In situ Raman spectra wer... more The interaction of Li + with single and few layer graphene is reported. In situ Raman spectra were collected during the electrochemical lithiation of the single-and few-layer graphene. While the interaction of lithium with few layer graphene seems to resemble that of graphite, single layer graphene behaves very differently. The amount of lithium absorbed on single layer graphene seems to be greatly reduced due to repulsion forces between Li + at both sides of the graphene layer.

Journal of The Electrochemical Society, 2008

Journal of The Electrochemical Society, 2009

Electrochemistry Communications, 2009

Early stages of the solid electrolyte interphase (SEI) formation at a tin foil electrode in an et... more Early stages of the solid electrolyte interphase (SEI) formation at a tin foil electrode in an ethylene carbonate (EC) based electrolyte were investigated by in situ AFM and cyclic voltammetry (CV) at potentials >0.7 V, i.e., above the potential of Sn-Li alloying. We detected and observed initial steps of the surface film formation at $2.8 V vs. Li/Li + followed by gradual film morphology changes at potentials 0.7 < U < 2.5 V. The SEI layer undergoes continuous reformation during the following CV cycles between 0.7 and 2.5 V. The surface film on Sn does not effectively prevent the electrolyte reduction and a large fraction of the reaction products dissolve in the electrolyte. The unstable SEI layer on Sn in EC-based electrolytes may compromise the use of tin-based anodes in Li-ion battery systems unless the interfacial chemistry of the electrode and/or electrolyte is modified.

Electrochemistry Communications, 2012

Spectroscopic ellipsometry was used to study the time-dependent formation of HF upon the thermal ... more Spectroscopic ellipsometry was used to study the time-dependent formation of HF upon the thermal degradation of LiPF 6 at 50°C in a lithium ion battery electrolyte containing ethylene carbonate and diethyl carbonate. The generated HF was monitored by following the etching rate of a 300 nm thick SiO 2 layer, grown on both sides of a silicon wafer substrate, as a function of the immersion time in the electrolyte at 50°C. It was found that the formation of HF starts after 70 hours of exposure time and occurs following several different phases. The amount of generated HF was calculated using an empirical formula correlating the etching rate to the temperature. Combining the results of the HF formation with literature data, a simplified mechanism for the formation of the HF involving LiPF 6 degradation, and a simplified catalytical reaction pathway of the formed HF and silicon dioxide is proposed to describe the kinetics of HF formation.

Electrochemistry Communications, 2007

... of lithium electrode introduces severe safety problems, so the advantages of ionic liquids in... more ... of lithium electrode introduces severe safety problems, so the advantages of ionic liquids in terms ... that in an electrolyte solution, based on the somewhat similar ionic liquid, N ... N-alkylpyrrolidinium bis(trifluoromethylsfonyl)imide, surface films are formed on lithium electrodes and ...

Carbon, 2006

The reaction of three types of carbon with oxygen (1 atm) at different temperatures was investiga... more The reaction of three types of carbon with oxygen (1 atm) at different temperatures was investigated. The precursors for the carbons studied were Kapton (polyimide), cellulose and cellulose that was carbonized with ammonium chloride. Two consecutive processes are confirmed to occur during the reaction with oxygen. The build up of oxygenated surface complexes by chemisorption of oxygen and the well-known gasification of these surface groups. The carbons originating from Kapton or cellulose carbonized in the presence of NH 4 Cl contain nitrogen. As the nitrogen content in the carbon is higher, the uptake of oxygen at the carbon surface by chemisorption is more pronounced. Hall effect measurements demonstrate that electrons are the major charge carrier in nitrogen containing carbons, while holes are the charge carriers in the nitrogen-free carbons. The determination of the type of charge carrier explains the observation that the nitrogen-containing carbons chemisorb oxygen more readily than the nitrogen-free carbons. Electronic conductivity demonstrates the affect of the sign of the charge carrier on the chemisorption of the carbons during chemisorption of oxygen. While in the case of n-type carbon a decrease in the conductivity was observed, p-type carbons exhibit a slight increase followed by a decrease in the conductivity.

Annual Review of Physical Chemistry, 1992

ACS Nano, 2011

The manipulation of the bandgap of graphene by various means has stirred great interest for poten... more The manipulation of the bandgap of graphene by various means has stirred great interest for potential applications. Here we show that treatment of graphene with xenon difluoride produces a partially fluorinated graphene (fluorographene) with covalent C-F bonding and local sp 3-carbon hybridization. The material was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, electron energy loss spectroscopy, photoluminescence spectroscopy, and near edge X-ray absorption spectroscopy. These results confirm the structural features of the fluorographane with a bandgap of 3.8 eV, close to that calculated for fluorinated single layer graphene, (CF) n. The material luminesces broadly in the UV and visible light regions, and has optical properties resembling diamond, with both excitonic and direct optical absorption and emission features. These results suggest the use of fluorographane as a new, readily prepared material for electronic, optoelectronic applications, and energy harvesting applications.