Olivine structured LiFe1/4Mn1/4Co1/4Ni1/4PO4 in pure solid solution single phase was obtained using solid-state reaction. For the carbon-coated material, in a voltage range of 3.0–5.1V (vs. Li/Li+), three voltage plateaus were observed clearly in both galvanostatic discharging and galvanostatic intermittent titration technique (GITT) curves. These three plateaus are corresponding to Co3+/Co2+, Mn3+/Mn2+ and Fe3+/Fe2+ redox couples. No definite plateau can be assigned to Ni3+/Ni2+ redox couple in this voltage range. The overpotentials show the maximum when the redox reaction shifts from one redox couple to another couple. The apparent chemical diffusion coefficients of lithium (D˜Li) are in the same order of magnitude 10−15cm2s−1 for all transition reactions.

The thermal and electrochemical stability, as well as compatibility with various bench mark cathode and anode materials of two new lithium fluoride salt (LiF) based electrolytes have been studied. These two new electrolytes are formed by using boron-based anion receptors, tris(pentafluorophenyl) borane (TPFPB), or tris(2H-hexafluoroisopropyl) borate (THFPB) as additives, which were designed and synthesized at Brookhaven National Laboratory (BNL), to dissolve the LiF salt in carbonate solvents. The transference number of Li+ for these electrolytes is as high as 0.7 and the room-temperature conductivity is around 2×10−3Scm−1. The electrolytes containing propylene carbonate (PC) show superior low-temperature conductivity properties. The electrochemical window is approaching 5.0V. It was also found that the new electrolytes work well with LiCoO2 or LiMn2O4 cathodes. However, when PC containing electrolytes were used, PC co-intercalation is still a problem for graphite anodes. The formation of a stable solid electrolyte interface layer on the surface of anode in this type of electrolyte needs to be studied further.

A new system of electrolytes has been developed and studied for lithium-ion batteries. This new system is based on the interactions between Li2O or Li2O2 and tris(pentafluorophenyl) borane (TPFPB) in carbonate based organic solvents. This opens up a completely new approach in developing non-aqueous electrolytes. In general, the solubility of Li2O or Li2O2 is very low in organic solvents and the ionic conductivities of these solutions are almost undetectable. By adding certain amount of tris(pentafluorophenyl) borane (TPFPB), one type of boron based anion receptors (BBARs), the solubility of Li2O or Li2O2 in carbonate based solvents was significantly enhanced. In addition, the Li+ transference numbers of these new electrolytes measured were as high as 0.7, which are more than 100% higher than the values for the conventional electrolytes for lithium-ion batteries. The room-temperature conductivities are around 1×10−3S/cm. These new electrolytes are compatible with LiMn2O4 cathode for lithium-ion batteries.

The new electrolyte systems utilizing one type of Lewis acids, the boron based anion receptors (BBARs) with LiF, Li2O, or Li2O2 in carbonate solutions have been developed and reported by us. These systems open up a new approach in developing non-aqueous electrolytes with higher operating voltage and less moisture sensitivity for lithium-ion batteries. However, the formation of a stable solid electrolyte interphase (SEI) layer on the graphitized anodes is a serious problem needs to be solved for these new electrolyte systems, especially when propylene carbonate (PC) is used as a co-solvent. Using lithium bis(oxalato)borate (LiBOB) as an additives, the SEI layer formation on mesophase carbon microbeads (MCMB) anode is significantly enhanced in these new electrolytes containing boron-based anion receptors, such as tris(pentafluorophenyl) borane, and lithium salt such as LiF, or lithium oxides such as Li2O or Li2O2 in PC and dimethyl carbonate (DMC) solvents. The cells using these electrolytes and MCMB anodes cycled very well and the PC co-intercalation was suppressed. Fourier transform infrared spectroscopy (FTIR) studies show that one of the electrochemical decomposition products of LiBOB, lithium carbonate (Li2CO3), plays a quite important role in the stablizing SEI layer formation.

We examined the oxidation state and local structure of hydrated ambigel V(2)O(5)(.)0.5H(2)O composite cathodes cycled in a nonaqueous electrolyte lithium cell. Changes in the oxidation state and local structure were monitored by X-ray absorption spectroscopy under in situ conditions. The cathodes had initial discharge capacities in the range 440-480 mAh/g, which correspond to an intercalation of 3.1-3.4 Li per V(2)O(5)(.)0.5H(2)O. Analyses of X-ray absorption near-edge structure data reveal that the average oxidation state of vanadium for discharged cathodes increased with cycling in the range of 1-17 cycles and then remained unchanged with further cycling. The oxidation state for charged cathodes remained relatively unchanged with cycling in the range of 1-40 cycles. The lack of strong contributions from higher coordination spheres in the Fourier transforms of extended X-ray absorption fine structure spectra of charged and discharged cathodes indicate that the amorphous nature of the material is retained during cycling. However, a significant increase in the amplitude of the V-O contribution is observed with prolonged cycling for both discharged and charged cathodes, which is likely due to the formation of irreversible phases with increased local symmetry for the V-O coordination geometry. The observed results for the ambigel material cycled in the range of 1-16 cycles are consistent with results previously observed for an aerogel material. (c) 2005 The Electrochemical Society. All rights reserved.

The Advanced Technology Development (ATD) Program is a multilaboratory effort to assist industrial developers of high-power lithium-ion batteries overcome the barriers of cost, calendar life, abuse tolerance, and low-temperature performance so that this technology may be rendered practical for use in hybrid electric vehicles (HEVs). Included in the ATD Program is a comprehensive diagnostics effort conducted by researchers at Argonne National Laboratory (ANL), Brookhaven National Laboratory (BNL), and Lawrence Berkeley National Laboratory (LBNL). The goals of this effort are to identify and characterize processes that limit lithium-ion battery performance and calendar life, and ultimately to describe the specific mechanisms that cause performance degradation. This report is a compilation of the diagnostics effort conducted since spring 2001 to characterize Generation 2 ATD cells and cell components. The report is divided into a main body and appendices. Information on the diagnostic approach, details from individual diagnostic techniques, and details on the phenomenological model used to link the diagnostic data to the loss of 18650-cell electrochemical performance are included in the appendices. The main body of the report includes an overview of the 18650-cell test data, summarizes diagnostic data and modeling information contained in the appendices, and provides an assessment of the variousmore » mechanisms that have been postulated to explain performance degradation of the 18650 cells during accelerated aging. This report is intended to serve as a ready reference on ATD Generation 2 18650-cell performance and provide information on the tools for diagnostic examination and relevance of the acquired data. A comprehensive account of our experimental procedures and resulting data may be obtained by consulting the various references listed in the text. We hope that this report will serve as a roadmap for the diagnostic analyses of other lithium-ion technologies being evaluated for HEV applications. It is our hope that the information contained in this report will lead to the development of new lithium-ion cell chemistries and designs that will meet the 15-year cell calendar-life goal established by DOE's FreedomCar and Fuel Partnership.« less

An active anode electrocatalyst, consisting of 1/8 of a monolayer of Pt on a surface of carbon-supported Ru nanoparticles, has been shown to exhibit excellent long-term performance stability in an operating fuel cell. The electrocatalyst has the reduced susceptibility to poisoning by CO, which, in addition to the strong segregation of the Pt atoms on the Ru substrate, determines this characteristic. Kinetic parameters were determined by electrochemical techniques using thin-film rotating disk electrodes. X-ray absorption spectroscopy near edge structure was used to determine the d-band vacancies of a Pt submonolayer on a surface of carbon-supported Ru nanoparticles, and to relate it to the bonding strength of CO. The data point the way to ultimately reduce Pt content in anode electrocatalysts while maintaining their high activity and thereby alleviating the problem of high Pt loading in existing fuel cell technology.

A new series of anion receptors based on boronate compounds have been synthesized. These compounds can be used as anion receptors in lithium battery electrolytes. The so-called boronate means that the compounds contain a boron bonded with two oxygen atoms and one carbon atom. This series includes various boronate compounds with different fluorinated aryl and fluorinated alkyl groups. When these anion receptors are used as additives in 1,2-dimethoxyethane (DME) solutions containing various lithium salts, the ionic conductivities of these solutions are greatly increased. The electrolytes tested in this study were DME solutions containing the following lithium salts: LiF, CF3COOLi, and C2F5COOLi. Without the additive, the solubility of LiF in DME (and all other nonaqueous solvents! is very low. With some of these boronate compounds as additives, LiF solutions in DME with concentration as high as 1 M were obtained. The solubilities of the other salts were also increased by these additives. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy studies show that I- anions are complexed with these compounds in DME solutions containing LiI salts. The degree of complexation is also closely related to the structures of the fluorinated aryl and alkyl groups which act as electron-withdrawing groups. The NEXAFS results are in good agreement with ionic conductivity studies. (C) 2004 The Electrochemical Society.

This paper is a full version of an earlier short communication, where significantly higher (up to threefold) CO tolerance was reported for PtMo/C (atomic ratio, Pt:Mo, 3:1) relative to the current state-of-the-art PtRu/C (1: 1) in a proton exchange membrane fuel cell (PEMFC) under standard operating conditions (85degreesC, 100% humidification, with H-2 + 100 pm CO//O-2). We report significantly different behavior for PtMo/C in contrast to PtRu/C, wherein there is negligible variation in CO tolerance (100 ppm CO in H-2) with variations in alloying compositions (Pt:Mo, 1: 1 to 5: 1). Further, in contrast to Pt/C and PtRu/C, significantly lower variations in overpotential losses is observed for PtMo/C as a function of temperature (55-115degreesC) and CO concentrations (5-100 ppm, balance H-2). In addition, excellent long-term stability is reported for PtMo/C (1:1) under steady-state conditions (constant potential conditions at 0.6 V) for a total duration of 1500 h, with anode gas composition varied between pure H-2 and those with 100 ppm CO, with or without the presence of other reformate gases (primarily CO2 and N-2). These are discussed in the context of detailed physicochemical characterization of the nanoparticles using a combination of X-ray diffraction, transmission electron microscopy, and in situ synchrotron X-ray absorption spectroscopy. (C) 2004 The Electrochemical Society.

Partial substitution of Mn in lithium manganese oxide spinel materials by Cu and Ni greatly affects the electrochemistry and the cycle life characteristics of the cathode. Substitution with either metal or a combination of both metals in the spinel lattice structure reduces the 3.9–4.2V potential plateaus associated with the conversion of Mn3+ to Mn4+. Higher potential plateau associated with oxidation of the substituted transition elements is also observed. These substituents also significantly alter the onset of Jahn–Teller distortions in the 3V potential plateau. Synchrotron based in situ X-ray absorption (XAS) was used to determine the exact nature of the oxidation state changes in order to explain the overall observed capacities at different potential plateaus. The studies on LiCu0.5Mn1.5O4 show single phase behavior in the 4–5V potential region with a good cycle life. Lower cycle life characteristic observed in cycling LiNi0.5Mn1.5O4 and LiNi0.25Cu0.25Mn1.5O4 versus Li metal are ascribed to coexistence of several phases in this potential region. However, LiCu0.5Mn1.5O4 shows onset of Jahn–Teller distortions in the 3V potential plateau, in contrast to LiNi0.5Mn1.5O4 and LiNi0.25Cu0.25Mn1.5O4 cathode materials.

Layered Li[Li0.3Cr0.1Mn0.6]O2 cathode material with a hexagonal structure was synthesized by a solid-state reaction. The structural changes of this material were studied using a synchrotron-based in situ X-ray diffraction (XRD) technique during charge/discharge cycles. The results of in situ X-ray diffraction indicated that the layer structure and the hexagonal symmetry of this material were preserved through the phase transition between H1 and H2 during the charge/discharge cycling. When cycled in the voltage range of 2.0–4.5 V, the changes in lattice parameters a and c are smaller than those for the LiNiO2 layered material. When charged to a high voltage at 5.1 V, the hexagonal phase H3, which is commonly formed at voltages higher than 4.3 V in LiNiO2 with a very short c-axis, is not observed in the Li[Li0.3Cr0.1Mn0.6]O2 cathode, indicating a possible high thermal stability in the fully charged state. Cyclic voltammograms show a single pair of oxidation and reduction peaks, consistent with a reversible phase transition between H1 and H2 observed from the in situ X-ray diffraction data.

Pd particles were inserted into polythiophene (PT) films and studied for the activity for the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in acid media. In situ X-ray absorption spectroscopy (XAS) was employed for the characterization of the Pd particles and the results confirmed that they possess metallic character. At low potentials, hydrogen is incorporated into the Pd lattice resulting in an increase in both the average Pd-Pd bond distance as well as the structural disorder. XAS results also indicated that a considerable fraction of the total Pd atoms is located in the surface of the electrodeposit, as expected for such a high surface area material. No activity for the HOR is seen for the PT films in the absence of catalysts. For the catalyzed PT films, a chemical reaction involving atomic adsorbed hydrogen atoms on Pt or Pd and the carbon radical in the polaronic PT species may occur causing a progressive degradation of the film properties during HOR. The Pd-modified electrode exhibits a considerable catalytic activity for ORR. Above 0.3 V, only formation of hydrogen peroxide occurs, leading to a two electron ORR mechanism. For smaller potentials, further reduction of H2O2 to water occurs, resulting in a four electron global process. (C) 2003 The Electrochemical Society.