Ronit Sharabi

Fluoroethylene carbonate as an important component in electrolyte solutions for high-voltage lithium batteries: role of surface chemistry on the cathode.

The effect of fluorinated ethylene carbonate (FEC) as a cosolvent in alkyl carbonates/LiPF6 on the cycling performance of high-voltage (5 V) cathodes for Li-ion batteries was investigated using electrochemical tools, X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HRSEM). An excellent cycling stability of LiCoPO4/Li, LiNi0.5Mn1.5O4/Si, and LiCoPO4/Si cells and a reasonable cycling of LiCoPO4/Si cells was achieved by replacing the commonly used cosolvent ethylene carbonate (EC) by FEC in electrolyte solutions for high-voltage Li-ion batteries. The roles of FEC in the improvement of the cycling performance of high-voltage Li-ion cells and of surface chemistry on the cathode are discussed.

In Situ FTIR Spectroscopy Study of Li / LiNi0.8Co0.15Al0.05O2 Cells with Ionic Liquid-Based Electrolytes in Overcharge Condition

We developed a methodology of in situ Fourier transform infrared (FTIR) measurements of gaseous products formed in an electrochemical cell upon polarization. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathodes were explored at potentials of up to 5.5 V vs Li in the ionic liquid (IL)-based electrolyte solution, LiTFSI/N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. The polarization of the NCA electrodes formed CO 2 and CO due to the liberation of oxygen and the parallel dissolution of nickel ions, which oxidizes the carbon black in the composite electrode. The oxygen was mostly liberated from the NCA and also due to minor contribution from the surface groups on the carbon black additive.

On the Surface Chemistry of Cathode Materials in Li-Ion Batteries

The main cathode materials for Li batteries include the following systems: transition metal oxides and sulfides (MO x , MS x ), lithiated transition metal oxides and sulfides (Li x MO y , Li x MS y ), and LiMPO4 olivine compounds. There are also oxygen- and sulfur-based cathodes whose main solid components are carbonaceous materials. Most of these cathodes develop very rich surface chemistry that affects very strongly their electrochemical performance. The main reactions are acid–base reactions (with acidic solution species, HF, PF5, PF3O, etc.); nucleophilic reactions between the basic compounds and the electrophilic alkyl carbonate solvents; polymerization; possible oxidation of solution species; and dissolution of transition metal ions. The behavior of many cathodes in Li-ion batteries is controlled by surface-film formation, passivation phenomena, and Li-ion migration through solid electrolyte interphases formed on the active mass by spontaneous reactions. We describe herein major surface processes, techniques that can address and analyze them, as well as means to improve the performance of cathodes in Li-ion batteries by controlling their surface phenomena.

Direct Electro-oxidation of Dimethyl Ether on Pt-Cu NanoChains

A new platinum-copper alloy electrocatalyst for the direct electro-oxidation of dimethyl ether (DME) has been synthesized in an easy and low-cost approach and studied by using an array of techniques, including X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and elemental analysis. Structural characterization revealed that the synthesized PtCu nanoparticles (3 nm on average) formed homogeneous nanochains without aggregation of metallic platinum or copper. The catalysts activity towards electro-oxidation of DME was tested using cyclic voltammetry (CV) and in membrane-electrode assembly (MEA) in a full cell and was found to be promising. The direct DME fuel cell (DDMEFC) studied in this work has relatively high energy density, of 13.5 mW cm-1 and thus shows great potential as fuel for low power fuel cells. The newly synthesized PtCu catalyst exhibited almost double the performance of commercial PtRu in electrocatalytic DME oxidation.