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Gromadskyi D.G.,8A Vernadsky Ave. | Gromadskyi D.G.,Kharkiv Polytechnic Institute
Journal of Chemical Sciences | Year: 2016

Silver metal covered by Ag2SO4 was investigated as a reference electrode for flat three-electrode cells. The potential stability of the Ag/Ag2SO4 electrode in neutral aqueous solutions utilized as electrolytes for asymmetric high-voltage supercapacitors is reported. It was found that the potential drift and temperature coefficient of this reference electrode are insignificant. Its use as an alternative to the Ag/AgCl electrode enables one to avoid the contamination of the supporting electrolyte solution by Cl − anions, which are oxidized earlier than water molecules and other oxygen-containing anions (SO42− or NO3−). Using the data obtained from three-electrode electrochemical measurements with the electrode in question, a graphene–carbon nanotube/MnO 2 supercapacitor cell accumulating 9.8 Wh kg −1 of specific energy at 1.75 V was built. [Figure not available: see fulltext.] © 2016, Indian Academy of Sciences.

Potapenkoa A.V.,8A Vernadsky Ave. | Kirillov S.A.,8A Vernadsky Ave. | Kirillov S.A.,Institute for Sorption and Problems of Endoecology
Journal of Energy Chemistry | Year: 2014

In order to successively compete with supercapacitors, an ability of fast discharge is a must for lithium-ion batteries. From this point of view, stoichiometric and substituted lithium manganese spinels as cathode materials are one of the most prospective candidates, especially in their nanosized form. In this article, an overview of the most recent data regarding physico-chemical and electrochemical properties of lithium manganese spinels, especially, LiMn2O4 and LiNi0.5Mn1.5O4, synthesized by means of various methods is presented, with special emphasis of their use in high-rate electrochemical applications. In particular, specific capacities and rate capabilities of spinel materials are analyzed. It is suggested that reduced specific capacity is determined primarily by the aggregation of material particles, whereas good high-rate capability is governed not only by the size of crystallites but also by the perfectness of crystals. The most technologically advantageous solutions are described, existing gas in the knowledge of spinel materials are outlined, and the ways of their filling are suggested, in a hope to be helpful in keeping lithium batteries afloat in the struggle for a worthy place among electrochemical energy systems of the 21st century. Copyright © 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. All rights reserved.

Potapenko A.V.,8A Vernadsky Ave. | Chernukhin S.I.,8A Vernadsky Ave. | Kirillov S.A.,8A Vernadsky Ave. | Kirillov S.A.,Institute for Sorption and Problems of Endoecology
Materials for Renewable and Sustainable Energy | Year: 2015

Lithium manganese spinels tend to aggregate upon annealing and do not allow for attaining high discharge rates when used as cathodes in lithium-ion batteries. To obtain spinel samples of lower aggregation and better high-rate properties, precursors synthesized by means of a citric acid-aided route are suggested to be pyrolyzed in an inert atmosphere, instead of pyrolysis in air. The synthesis of nanosized Li[Li0.033Mn1.967]O4 is described, and its characteristics including X-ray diffraction, scanning electron microscopy, and porosity, as well as electrochemical test results are presented. The particle size of the materials obtained is smaller, the degree of aggregation is lower, and high-rate properties are better than for analogues pyrolyzed in air. In particular, sample Li||Li[Li0.033Mn1.967]O4 cells deliver ~60 mAh g-1 at the current loads of 4,000 mA g-1 (30 C). After a sequence of 62 charge/discharge cycles with the currents growing from 0.1 to 100 C the specific capacity retains its initial value. © 2014 The Author(s).

Tretyakov D.O.,8A Vernadsky Ave. | Prisiazhnyi V.D.,8A Vernadsky Ave. | Gafurov M.M.,Kh A Amirkhanov Institute Of Physics | Rabadanov K.S.,Kh A Amirkhanov Institute Of Physics | And 2 more authors.
Journal of Chemical and Engineering Data | Year: 2010

This work reports phase diagrams, conductivity isotherms, and data regarding the structure and dynamics of systems formed by lithium perchlorate and nitrate as solutes and sulfones as solvents. The LiClO4 + (CH3)2SO2 system behaves like typical electrolytic systems containing a lithium salt and a solvent and forms a 1:1 solvate; its conductivity isotherm demonstrates a maximum. Unlike typical systems, the phase diagrams of the LiNO3 + (CH3) 2SO2 and LiNO3 + (C2H 5)2SO2 systems appear to be simple eutectic. The dependences of specific conductivity on the concentration of LiNO 3 are also uncommon showing no maximum characteristic to electrolyte solutions. Raman studies and analysis of dynamics performed using Raman data signify that, in the LiClO4 + (CH3)2SO 2 system, solvated cations and contact ion pairs exist. In the LiNO3 + (CH3)2SO2 system, contact ion pairs are present as well, but signatures of cation solvation cannot be found. © 2010 American Chemical Society.

Kirillov S.A.,8A Vernadsky Ave. | Gorobets M.I.,8A Vernadsky Ave.
Journal of Molecular Liquids | Year: 2014

Raman study of ion pairing in dimethyl sulfoxide (DMSO), propylene carbonate (PC) and dimethyl carbonate (DMC) solutions of five lithium salts has been performed in the concentration range from 0.05 to 0.25 molar fraction of a salt and the dependences of the amount of the free anions, solvent separated ion pairs (SSIPs) and contact ion pairs (CIPs) on salt concentrations have been determined, which significantly differ from salt to salt and from one solvent to another. In DMSO solutions, at 0.075 mole fraction of a salt, when the conductivity maximum is showing up, the order for increasing concentration of anions is BF4 -< ClO4 -< N(SO3CF3)2 -≤ B(C2O4)2 -< CF3SO3 -, and the order for decreasing concentration of SSIPs is BF4 -> ClO4 -> B(C2O4)2 -≥ N(SO3CF3)2 -> CF3SO3 -. These do not coincide with the order for increasing conductivity, probably signifying the influence of other factors, like the mass and radius of charge carriers, on conductivity. In the LiClO4-DMSO, LiClO4-PC and LiClO4-DMC systems, the order of solvents for increasing concentration of free anions as PC = DMC(= 0) < < DMSO and that for decreasing concentration of SSIPs as DMC > PC > DMSO at cLiClO4= 0.075 mole fraction perfectly coincide with the order of solvents for increasing conductivity as DMC < PC < < DMSO. This means that no free ions exist in the PC and DMC solutions at cLiClO4= 0.075 mole fraction, and their conductance is solely ensured by SSIPs. © 2014 Published by Elsevier B.V.

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