The electrochemical reduction of oxygen was investigated in some hydrophobic room-temperature molten salt systems (ionic liquids) consisting of bis(trifluoromethanesulfone)imide false(TFSI−false) anion with trimethyl-n-hexylammonium false(TMHA+false), 1-butyl-1-methylpyrrolidinium false(BMP+false), 1-ethyl-3-methylimidazolium false(EMI+false) or 1,2-dimethyl-3-propylimidazolium false(DMPI+false) cation. The oxygen dissolved in these melts was reduced to the superoxide ion on a gold electrode. The superoxide ion was stable against the aliphatic and alicyclic organic cations false(TMHA+ and BMP+false) but reacted with the aromatic ones false(EMI+ and DMPI+false), suggesting that nucleophilic reagents attack the melts consisting of imidazolium cations. The acceptor number of these TFSI− -based molten salt systems was estimated to be comparable to those of acetonitrile and dimethyl sulfoxide from the comparison of the redox potential of O2/O2−. The superoxide ion was further reduced, presumably to the peroxide, on a gold electrode in the melts consisting of the aliphatic or alicyclic organic cation. © 2003 The Electrochemical Society. All rights reserved.

To study the effect of different polymer binders on electrochemical performance of the Si composite electrode in rechargeable lithium-ion batteries, sodium polyacrylate (PAANa), sodium carboxymethyl cellulose (CMCNa), and poly(vinylidene fluoride) (PVdF) are utilized as the polymer binders for the preparation of composite electrodes consisting of powdery silicon, graphite, and Ketjen black. The electrodes are examined by cross-sectional observation using a scanning electron microscope after a focused ion beam process, X-ray photoelectron spectroscopy, micro Raman spectroscopy, X-ray diffraction, and a peel test. We report that electrode performance of the Si composites depends on a selection of binders, and PAANa binder remarkably improves the electrochemical lithiation and delithiation performance of the Si–graphite composite electrode compared to that of conventional binders of PVdF and CMCNa. When the electrode is prepared with 30 wt % PAANa binder, the higher initial efficiency is obtained with much improved cyclability. Furthermore, the specific capacity of the electrode reaches 1000 mAh g–1 and exceeds 800 mAh g–1 of reversible capacity during the 30 continuous cycling test. The PAANa polymer binder increases the mechanical strength and adhesive strength as composite electrodes. Furthermore, the polymer layer reduces the electrolyte decomposition at the Si particles and suppresses the capacity deterioration by volume change and pulverization due to Si–Li alloying, compared with PVdF, leading to the better electrochemical reversibility.

The electrochemical behavior of oxygen ͑O 2 ͒/superoxide ion ͑O 2 − ͒ couple was investigated with the aid of the ultramicroelectrode technique in 1-butyl-1-methylpyrrolidinium bis͑trifluoromethylsulfonyl͒imide ͑BMPTFSI͒ room-temperature molten salt ͑ionic liquid͒. The diffusion coefficient of O 2 was ͑1.8 ± 0.2͒ ϫ 10 −6 cm 2 s −1 at 25°C. The activation energy of the diffusion process of O 2 was estimated to be 27 kJ mol −1 from the temperature dependence of the diffusion coefficient. The solubility of O 2 in BMPTFSI was 14 mmol dm −3 at 25°C and decreased with an increase in temperature. The diffusion coefficient of O 2 − was 0.86 ϫ 10 −6 cm 2 s −1 at 25°C. The formal potential of O 2 /O 2 − couple was 1.13 V vs ferrocene/ferrocenium.

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Graphite/silicon composite electrodes are prepared with PANa polymer as a binder. Morphological characters and electrode performance are compared with those of PVdF. The PANa layer behaves like SEI at the interface with ionic liquid, resulting in the highly reversible electrode performance.