J.S. Gnanaraja, E. Zinigrada, M.D. Levia, D. Aurbacha,*, M. Schmidtb

a Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel

b Merck KGaA, D-64293 Darmstadt, Germany

2.Experimental

The electrolyte solutions used were 1 M LiFAP, 1 MLiPF6, and 1 M LiN(SO2CF2CF3)2in a ternary solvent mixture EC+DEC+DMC (2:1:2) from Merck KGaA (highly pure solutions, Li battery grade, could be used as received). All the work was performed under a highly pure argon atmosphere in standard vacuum glove box .The anodes were composed of synthetic graphite (KS-6) from Timrex Inc. (average particle size ca. 6 mm, 90 wt.%), PVdF binder (10 wt.%) from Solvey Inc., and copper foil current collectors. The cathodes were comprised of LiMn2O4powder from Merck KGaA (particle size of 5–10 mm, 75 wt.%), 15 wt.% graphite powder KS-6 (xiamen Tmaxcn Inc.) as a conductive additive, 5 wt.% PVdF, 5 wt.% conductive carbon black, and an aluminum foil (Goodfellow,England) current collector. Slurries containing the active mass and the binder were prepared using N-methyl pyrrolidone (Fluka Inc.) and were coated on the appropriate current collectors, as already described [6]. The electrodes were dried in an oven at 140 8C and were then transferred to the glove boxes. All the electroanalytical characterizations of the electrodes were performed in three-electrode cells based on standard coin-type cells (Model 2032, NRC Canada, f 19 mm). A Li wire reference electrode was pasted on a nickel wire, which was placed between the working electrode and the Li counter-electrode foil, while being covered by the separator membrane (Celgard 2400). Long-term cycling tests for graphite and LiMn2O4electrodes were performed in two-electrode standard coin-type cells,separated by a porous polypropylene membrane (Celgard Inc.). These cells were hermetically sealed in a dry air- fifilled glove box using the 2325 Coin Cell Crimper

A Maccor multichannel system (Model 2000) was used for prolonged galvanostatic cycling. For voltammetric measurements, an Arbin Inc. computerized multichannel battery tester and a computerized EG&G Model 273 potentiostat were used.

Impedance spectra were measured using the Autolab Model PGSTAT20 Electrochemical system and a frequency response analyzer (FRA) from Eco Chemie BV Inc., driven by a Pentium II IBM PC. The amplitude of the ac voltage was 3 mV and the impedance was measured at a constantbase potential after the appropriate equilibration. FTIR measurements of pristine and cycled electrodes were carried out in diffuse reflflectance mode using Magna 860 FTIR spectrometer (Nicolet Inc.), operating under H2O and CO2free atmosphere (in a homemade glove box).

We used ARC (Arthur D Little Inc. Model 2000) with5℃increments at the rate of 2℃/min in search for self heating at the sensitivity threshold of 0.02℃/min