Sn-Sb and Sn-Bi alloys as anode materials for lithium-ion batteries

Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi multi-phase materials were synthesised via reduction of cationic precursors with NaBH₄ and with Zn, and were tested for their suitability as anode materials for Li-ion batteries by galvanostatic cycling. The rapid reduction with NaBH₄ yielded the finer materials with the better cycling stabilities, whereas the reduction with Zn yielded the purer materials with the lower irreversible capacities in the first cycle. Reversible capacities of ∼ 600 mAh g⁻¹, ∼ 350 – 400 mAh g⁻¹, and ∼ 500 mAh g⁻¹ were obtained for Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi, respectively. The cycling stability of the materials decreased in the order Sn/SnSb>Sn/SnSb/Bi>Sn/Bi, which is in part attributed to the presence / absence of intermetallic phases which undergo phase-separation during lithiation. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

The role of surface oxides in formic acid oxidation on Au

Compared to Pt or Pd electrodes, Au is a poor catalyst for the direct anodic oxidation of HCOOH, but the formation of Au surface oxides in acidic solutions is accompanied by a fast oxidation of HCOOH. This fast reaction is not simply a secondary reaction of Au surface oxides since those oxides are kinetically stable in HCOOH solutions. They do oxidize HCOOH only via a slow and purely electrochemical process which occurs on free Au sites and is “driven” by oxide reduction. The fast HCOOH oxidation is due to a highly reactive intermediate which is able either to form stable Au oxides Au_nO_m or to react with HCOOH. Our results are consistent with the model that by the charge transfer step a reactive non-equilibrium {Au…O> species is formed which converts to stable equilibrium oxides Au_nO_m after migration and rearrangement steps. Pre-equilibrium <Au…O> oxidizes HCOOH and this oxidation is of lower order with respect to <Au…O> compared with the formation of Au_nO_m.     

Two-phase reaction mechanism during chemical lithium insertion into α-MoO<Subscript>3</Subscript>

The phase transition during chemical lithium insertion into α-MoO₃ was investigated by chemical analysis, X-ray diffraction (XRD) and electrochemical characterisation. The samples have been prepared by reaction of various amounts of water-free lithium iodide with fine-particulate orthorhombic molybdenum trioxide in n-hexane (non-aqueous media), which yielded materials with different Li/Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO₃ has been changed after the chemical lithiation. The phase transition ranged from 0.25 < x < 0.5 in Li _x MoO₃ upon chemical lithium insertion into α-MoO₃. The XRD lines of lithium inserted phase Li _x MoO₃ grew at the expense of the XRD lines of the pristine α-MoO₃ as lithium ions were chemically inserted until the disappearance of lines related to α-MoO₃. The electrochemical performance of the lithiated samples is improved in comparison with the starting material (non-lithiated α-MoO₃).     

Small particle size multiphase Li-alloy anodes for lithium-ionbatteries

An impressive improvement of the cycling performance of Li-alloy anodes (M + Li⁺ +e⁻ Li_xM) in rechargeable organic electrolyte lithium batteries can be achieved by replacing compact or large particle size metallic host matrices M (e.g. Sn or Sb) with small particle size (micro- or nano-scale) multiphase metallic host materials like Sn/SnSb_n or Sn/SnAg_n. Electrochemical alloy deposition is a convenient way to prepare sub-micrometer particles of Sn and SnSb_n or Sn and SnAg_n. During the first lithium insertion these small particle size multiphase matrix materials are expanded to a porous material, however, without formation of major cracks. This seems not only to be related with the small absolute changes in the size of the individual particles, but also with the fact that the more reactive particles are allowed to expand in a soft and ductile surrounding of still unreacted material.     

In situ studies of solid state reactions by perturbed angular correlation

We report on three examples of in situ studies of solid state reactions by time differential perturbed angular correlation of¹⁸¹Ta: (i) the oxidation of hafnium metal and the doping of ZrS₂ with Hf during iodine vapour transport crystal growth; (ii) the observation of sublattice melting during polymorphic phase transitions in TaS₂; (iii) the electrointercalation of 2H-TaS₂ with silver.     

Overview of DWDM/ODC Project

Abstract

This article introduces the main achievements resulting from the DWDM/ODC project. The five areas of research activity within the DWDM/ODC project cover some of the main issues of design and development of dense wavelength division multiplexing systems for transparent optical networks. These issues are: performance assessment with arbitrary optical filtering; performance of signaling formats; dispersion compensation strategies for directly and externally modulated systems in presence of nonlinear transmission-induced degradation; and the impact of noise and crosstalk in the extent of transparent optical networks. All five areas of research activity have contributed significantly to a better understanding of the limitations present in dense wavelength division multiplexing systems.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

Studies on the Anode/Electrolyte Interfacein Lithium Ion Batteries

Summary.  Rechargeable lithium ion cells operate at voltages of 3.5–4.5 V, which is far beyond the thermodynamic stability window of the battery electrolyte. Strong electrolyte reduction and anode corrosion has to be anticipated, leading to irreversible loss of electroactive material and electrolyte and thus strongly deteriorating cell performance. To minimize these reactions, anode and electrolyte components have to be combined that induce the electrolyte reduction products to form an effectively protecting film at the anode/electrolyte interface, which hinders further electrolyte decomposition reactions, but acts as membrane for the lithium cations, i.e. behaving as a solid electrolyte interphase (SEI). This paper focuses on important aspects of the SEI. By using key examples, the effects of film forming electrolyte additives and the change of the active anode material from carbons to lithium storage alloys are highlighted. Received May 30, 2000. Accepted June 14, 2000