William M. Lamanna

Corrosion of aluminum at high voltages in non-aqueous electrolytes containing perfluoroalkylsulfonyl imides; new lithium salts for lithium-ion cells

New lithium bis-perfluoroalkylsulfonyl imide salts were recently synthesized in our laboratories whose properties make them promising candidates for lithium-ion batteries. The salts have good conductivity, cycling characteristics and excellent thermal and hydrolytic stability. In the focus of this paper are the corrosion properties of the aluminum current collector in electrolytes based on these salts. High protection potentials at aluminum in bisperfluoroethylsulfonyl imide electrolytes were observed. Based on the surface analysis of the protective film, a correlation of the molecular weight of the anions to their protective properties was established.

The surface film formed on a lithium metal electrode in a new imide electrolyte, lithium bis(perfluoroethylsulfonylimide) [LiN(C2F5SO2)2]

A newly developed imide electrolyte salt, LiN(C 2 F 5 SO 2 ) 2 (LiBETI) was found to give very uniform, thin, and stable surface films on a lithium metal electrode in the propylene carbonate (PC) solution. LiBETI/PC was studied and compared to determine its ability to form such a stable surface film, with conventional electrolyte systems such as LiCF 3 SO 3 /PC, LiPF 6 /PC, and LiN(CF 3 SO 2 ) 2 /PC (LiTFSI/PC). The surface film formed in LiBETI/PC system was a hemispherical, and the composition of the film consisted mainly of LiF, which is similar to that in a LiPF 6 /PC system. Quartz crystal microbalance (QCM) and cyclic voltammetry (after the tenth cycle) indicated that the surface film formed in LiBETI/PC (ca. 50 nm) was thinner than those in LiPF 6 /PC (ca. 90 nm), LiTFSI/PC (ca. 140 nm), or LiCF 3 SO 3 /PC (ca. 255 nm). The variation of the resonance resistance (AR) obtained from in situ CV/QCM measurement, which has been demonstrated to be a good measure of the surface roughness, also suggested that LiBETI/PC system gave a compact and smooth surface topology during lithium deposition-dissolution cycles. Impedance spectroscopy together with preliminary cycling tests showed that the LiBETI/PC system provides the highest cycling efficiency and improved cycleability among existing electrolyte salt systems in rechargeable battery systems employing lithium metal anodes.

High-Potential Redox Shuttle for Use in Lithium-Ion Batteries

Redox shuttle additives can be used in lithium-ion cells to protect against overcharging and for cell balancing in multicell packs. Most previously reported redox shuttles have been either unstable as shuttles, resulting in a short duration of overcharge protection, or have redox potentials that make them suitable only for cells containing lower potential positive electrode materials, such as LiFePO 4 . A new molecule, l,4-di-t-butyl-2,5-bis(2,2,2-trifluoroethoxy)benzene, is shown here to be a stable redox shuttle with a redox potential of 4.25 V and provides overcharge protection in full Li-ion cells, implying adequate reductive stability. Experiments using Li/LiCoO 2 and Li/Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 cells show that this molecule can work with high-energy-density positive electrodes as well as in full cells containing LiFePO 4 positive electrodes and Li, mesocarbon microbead, or Li 4 Ti 5 O 12 negative electrodes.

Mechanism of olefin polymerization by a soluble zirconium catalyst

Abstract A mechanistic study has been carried out on the homogeneous olefin polymerization/oligomerization catalyst formed from Cp 2 ZrMe 2 and methylaluminoxane, (MeAlO) x , in toluene. Formal transfer of CH 3 from Zr to Al yields low concentrations of Cp 2 ZrMe + solvated by [(Me 2 AlO) y (MeAlO) x − y ] y . The cationic Zr species initiates ethylene oligomerization by olefin coordination followed by insertion into the Zr–CH 3 bond. Chain transfer occurs by one of two competing pathways. The predominant one involves exchange of Cp 2 Zr–P + (P=growing ethylene oligomer) with Al–CH 3 to produce another Cp 2 ZrMe + initiator plus an Al-bound oligomer. Terminal Al–C bonds in the latter are ultimately cleaved on hydrolytic workup to produce materials with saturated end groups. Concomitant chain transfer occurs by sigma bond metathesis of Cp 2 Zr–P + with ethylene. Metathesis results in cleavage of the Zr–C bond of the growing oligomer to produce materials also having saturated end groups; and a new initiating species, Cp 2 Zr-CHCH 2 + . The two chain transfer pathways afford structurally different oligomers distinguishable by carbon number and end group structure. Oligomers derived from the Cp 2 ZrMe + channel are C n ( n =odd) alkanes; those derived from Cp 2 Zr–CHCH 2 + are terminally mono-unsaturated C n ( n =even) alkenes. Chain transfer by beta hydride elimination is detectable but relatively insignificant under the conditions employed. Propylene and 1-hexene react similarly but beta hydride elimination is the predominant chain transfer step. The initial Zr-alkyl species produces a Cp 2 ZrH + complex that is the principle chain initiator. Chain transfer is fast relative to propagation and the products are low molecular weight oligomers.

A Combined Computational/Experimental Study on Tertbutyl- and Methoxy-Substituted Benzene Derivatives as Redox Shuttles for Lithium-Ion Cells

Calculations were performed on a group of 43 t-butyl- and methoxy-substituted benzenes to assess their suitability as redox shuttle additives for lithium-ion cells. One molecule of this type has been previously shown to be excellent for overcharge protection of mesocarbon microbead (MCMB)/LiFePO 4 and Li 4/3 Ti 5/3 O 4 /LiFePO 4 lithium-ion cells. These calculations showed that 2,5-di-t-butyl-1,4-dimethoxybenzene was the best molecule in this group, as far as oxidation potential and stability are concerned. Other molecules that showed promise were 2-t-butyl-l,4-dimethoxybenzene, 4-t-butyl-1,2-dimethoxybenzene, and 3,5-di-t-butyl-l,2-dimethoxybenzene. These molecules were synthesized and tested in coin-type cells to confirm the results expected based on the calculations. The results of the calculations show that the substitution pattern on the molecule can be used to predict the most reactive sites on the oxidized molecule. For the dimethoxy-substituted molecules, the calculations predict that the ortho and para substitution pattern results in more stable oxidized molecules than the meta pattern.

Perfluoroalkylsulfone reactions with nucleophiles

Perfluorodialkylsulfones were found to react readily with metal hydroxides in water or alcohol solution and with ammonia to form fluorinated sulfonic acid derivatives.

Fluorinated olefins and oleum

Abstract Oleum has some advantages over pure sulfur trioxide and may be successfully used for preparation of beta-sultones from hexafluoropropene, 2H-pentafluoropropene, 6H-perfluoro-1-hexene and perfluoro(propylvinyl) ether (VE). Depending on the reaction conditions, the VE-sultone and tetrafluoroethane-beta-sultone (TFE-sultone) are different from other sultones. They are not stable in the presence of oleum and the oxidation of –CF 2 –SO 2 -group in the sultones leads to some new fluorooxalate derivatives.