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Zinc electrode in alkaline electrolyte

Description: The zinc electrode in alkaline electrolyte is unusual in that supersaturated zincate solutions can form during discharge and spongy or mossy zinc deposits can form on charge at low overvoltages. The effect of additives on regular pasted ZnO electrodes and calcium zincate electrodes is discussed. The paper also reports on in situ x-ray absorption (XAS) results on mossy zinc deposits.
Date: December 31, 1995
Creator: McBreen, J.
Partner: UNT Libraries Government Documents Department

X-ray absorption studies of battery materials

Description: X-ray absorption spectroscopy (XAS) is ideal for {ital in}{ital situ} studies of battery materials because both the probe and signal are penetrating x rays. The advantage of XAS being element specific permits investigation of the environment of a constituent element in a composite material. This makes it very powerful for studying electrode additives and corrosion of individual components of complex metal hydride alloys. The near edge part of the spectrum (XANES) provides information on oxidation state and site symmetry of the excited atom. This is particularly useful in study of corrosion and oxidation changes in cathode materials during charge/discharge cycle. Extended fine structure (EXAFS) gives structural information. Thus the technique provides both chemical and structural information. Since XAS probes only short range order, it can be applied to study of amorphous electrode materials and electrolytes. This paper discusses advantages and limitations of the method, as well as some experimental aspects.
Date: October 1, 1996
Creator: McBreen, J.
Partner: UNT Libraries Government Documents Department

Synthesis and characterization of metal hydride electrodes. Interim report

Description: The objective of this project is to elucidate the compositional and structural parameters that affect the thermodynamics, kinetics and stability of alloy hydride electrodes and to use this information in the development of new high capacity long life hydride electrodes for rechargeable batteries. The work focuses on the development of AB{sub 5} alloys and the application of in situ methods, at NSLS, such as x-ray absorption (XAS), to elucidate the role of the alloying elements in hydrogen storage and corrosion inhibition. The most significant results to date are: The decay of electrode capacity on cycling was directly related to alloy corrosion. The rate of corrosion depended in part on both the alloy composition and the partial molar volume of hydrogen, V{sub H}. The corrosion rate depended on the composition of the A component in AB{sub 5} (LaNi{sub 5} type) alloys. Partial substitution of La with Ce in AB{sub 5} alloys substantially inhibits electrode corrosion on cycling. Recent results indicate that Co also greatly inhibits electrode corrosion, possibly by minimizing V{sub H}. The AB{sub 5} alloys investigated included LaNi{sub 5}, ternary alloys (e.g. LaN{sub 4.8}Sn{sub 0.2} and La{sub 0.8}Ce{sub 0.2}Ni{sub 5}), alloys with various substitutions for both La and Ni (e.g. La{sub 0.8}Ce{sub 0.2}Ni{sub 4.8}Sn{sub 0.2}) and mischmetal (Mm) alloys of the type normally used in batteries, such as MmB{sub 5} (B = Ni{sub 3.55}Mn{sub 0.4}A1{sub 0.3}Co{sub 0.75}). A major effort was devoted to the effects of La substitution in the A component. Both in situ and ex situ XAS measurements are used to study the electronic effects that occur on the addition of various metal substitutions and on the ingress of hydrogen.
Date: October 1, 1995
Creator: McBreen, J. & Reilly, J.J.
Partner: UNT Libraries Government Documents Department

NICKEL HYDROXIDES

Description: Nickel hydroxides have been used as the active material in the positive electrodes of several alkaline batteries for over a century. These materials continue to attract a lot of attention because of the commercial importance of nickel-cadmium and nickel-metal hydride batteries. This review gives a brief overview of the structure of nickel hydroxide battery electrodes and a more detailed review of the solid state chemistry and electrochemistry of the electrode materials. Emphasis is on work done since 1989.
Date: November 1997
Creator: McBreen, J.
Partner: UNT Libraries Government Documents Department

The effect of Ru and Sn additions to Pt on the electrocatalysis of methanol oxidation: An in situ XAS investigation

Description: Elements such as Ru and Sn used as ad-atoms or as alloying elements are known to enhance methanol oxidation reaction (MOR). Ru, both as alloying element as well as upd deposited on Pt/C is widely acknowledged for enhancing MOR. Sn on the other hand is more controversial, with evidence indicating enhancements for MOR when present as upd layer and marginally effective when present as an alloying element. In situ XAS is used to investigate some of these inconsistencies in the electrocatalysis of MOR. Results indicate that alloying Sn with Pt (Pt{sub 3}Sn primary phase) causes partial filling of the Pt 5 d-band vacancies and increase in the Pt-Pt bond distances which is directly opposite to a similar situation with Ru. Upd Sn however does not perturb Pt structurally or electronically. Ru and Sn (both as alloying element and as upd ad-layer) are associated with oxygenated species, the nature and strength of the Ru. and Sn - oxygen interactions are potential dependent. Hence alloying with Sn renders Pt surface unfavorable for methanol adsorption in contrast to alloying with Ru. Both Ru and Sn however promote MOR via their ability to nucleate oxygenated species on their surface at lower potentials as compared to pure Pt.
Date: July 1, 1997
Creator: Mukerjee, S. & McBreen, J.
Partner: UNT Libraries Government Documents Department

SYNTHESIS OF A NEW FAMILY OF FLUORINATED BORONATE COMPOUNDS AS ANION RECEPTORS AND STUDIES OF THEIR USE AS ADDITIVES IN LITHIUM BATTERY ELECTROLYTES.

Description: Numerous studies have been done on developing new electrolytes for lithium batteries with high ionic conductivity, and good chemical and electrochemical stability. In addition to the research on new salts and solvents, the use of cation receptors to reduce ion pairing in non-aqueous electrolytes has been considered as an approach to improve the properties of electrolytes. Although both cation and anion receptors enhance the dissociation of ion pairs and increase the conductivity of electrolytes, the use of anion receptors is more attractive for a lithium battery electrolyte because anion receptors increase the lithium transference number in the electrolyte. However, most available neutral anion receptors complex with anions through hydrogen binding and cannot be used in lithium batteries. Recently, we have reported on synthesis of a series of new neutral boron compounds as anion receptors based on the idea that electron-deficient boron would complex the anion of the ion pair. The anion complexation effect of these boron compounds was further enhanced by attaching electron-withdrawing groups. Here we report synthesis of another new family of boronate compounds. The effect of these new compounds on conductivity of lithium salts in non-aqueous solution was studied. The molecular weights of these new boronate compounds are lower than our previously reported boron compounds. Therefore, their effects on conductivity enhancement are superior. They also display high electrochemical stability up to 5 V.
Date: June 8, 2001
Creator: MCBREEN,J.; LEE,H.S. & YANG,X.Q.
Partner: UNT Libraries Government Documents Department

A SYSTEMATIC STUDY OF INTERCALATION COMPOUNDS AS CATHODE MATERIALS FOR LITHIUM BATTERIES.

Description: Three types of intercalation Compounds, LiMn{sub 2}O{sub 4} with spinel structure, LiNiO{sub 2} and LiCoO{sub 2} with layered structure are widely studied as cathode materials for lithium-ion batteries. Among them, LiCoO{sub 2} is the most widely used cathode material in commercial lithium battery cells. LiNiO{sub 2} has same theoretical capacity as LiCoO{sub 2}, but is less expensive. However its application in lithium batteries has not been realized due to serious safety concerns. Substituting a portion of Ni in LiNiO{sub 2} with other cations has been pursued as a way to improve its safety characteristics. It was reported that Co doped LiNi{sub 0.8}Co{sub 0.2}O{sub 2} showed better thermal stability than pure LiNiO{sub 2}. Many new materials have been developed aimed in increasing the capacity and improving the thermal stability and cyclability. Most of these new materials are based on these three types of materials and modified their compositions and structures by doping. However, most of the efforts on developing new cathode materials have been done on the empirical base without guidelines from the systematic studies on the relationship between the performance and the structural changes of the cathode materials. Exploring this relationship is very important not only in guiding the development of new materials, but also in improving the performance and safety aspect for the existing cathode materials for lithium ion batteries. Using conventional x-ray source and a specially designed battery cell with beryllium windows, Dahn and co-workers have published several papers on the structural changes of LiNiO{sub 2} cathodes 1 and LiCoO{sub 2} cathodes 2 during charge. Unfortunately, the charging voltage was limited to below 4.3 V due to the problem of beryllium window corrosion at higher voltage. However, the voltage range between 4.3 V and 5.2 V is the most important region for studying the relationship between the thermal ...
Date: June 8, 2001
Creator: YANG,X.Q. & MCBREEN,J.
Partner: UNT Libraries Government Documents Department

New Findings on the Phase Transitions in Li(sub 1-x)CoO(sub 2) and Li(sub 1-x)NiO(sub 2) Cathode Materials During Cycling: In Situ Synchrotron X-Ray Diffraction Studies

Description: The authors have utilized synchrotron x-ray radiation to perform ''in situ'' x-ray diffraction studies on Li{sub 1-x}CoO{sub 2} and Li{sub 1-x}NiO{sub 2} cathodes. A C/10 charging rate was used for a Li/Li{sub 1-x}CoO{sub 2} cell. For the Li/Li{sub 1-x}NiO{sub 2} cells, C/13 and C/84 rates were applied. The in situ XRD data were collected during the first charge from 3.5 to 5.2 V. For the Li{sub 1-x}CoO{sub 2} cathode, in the composition range of x = 0 to x = 0.5, a new intermediate phase H2a was observed in addition to the two expected hexagonal phases H1 and H2. In the region very close to x = 0.5, some spectral signatures for the formation of a monoclinic phase M1 were also observed. Further, in the x = 0.8 to x = 1 region, the formation of a CdI{sub 2} type hexagonal phase has been confirmed. However, this new phase is transformed from a CdCl{sub 2} type hexagonal phase, rather than from a monoclinic phase M2 as previously reported in the literature. For the Li{sub 1-x}NiO{sub 2} system, by taking the advantage of the high resolution in 2{theta} angles through the synchrotron based XRD technique, they were able to identify a two-phase coexistence region of hexagonal phase H1 and H2, which has been mistakenly indexed as a single phase region for monoclinic phase M1. Interesting similarities and differences between these two systems are also discussed.
Date: October 17, 1999
Creator: Yang, X. Q.; Sun, X. & McBreen, J.
Partner: UNT Libraries Government Documents Department

In situ synchrotron x-ray studies of LiMn{sub 2}O{sub 4} cathodes

Description: LiCoO{sub 2} cathodes are now used in most commercial lithium ion batteries. LiMn{sub 2}O{sub 4} is an attractive low cost alternative. However, it is difficult to make reproducibly. At Brookhaven National Laboratory two in situ synchrotron x-ray techniques, that are available at the National Synchrotron Light Source (NSLS), have been used to investigate LiMn{sub 2}O{sub 4}. The techniques are x-ray absorption and high resolution x-ray diffraction. With x-ray absorption it is possible to follow the changes in the Mn oxidation state and the changes in the Mn-O and Mn-Mn bond lengths on cycling. Also it is possible to detect amorphous phases. The high energy x-rays at the diffraction Beam Lines at the NSLS (up to 24 KeV) permit in situ x-ray diffraction, in the transmission mode, in thin lithium and lithium ion cells. The evolution of the structural chances that occur on cycling can be followed. These in situ measurements were done on Li/LiMn{sub 2}O{sub 4} cells with a liquid electrolyte (1 M LiPF{sub 6} in a 1:1:3 PC:EC:DMC solvent).
Date: May 1997
Creator: McBreen, J.; Mukerjee, S. & Yang, X. Q.
Partner: UNT Libraries Government Documents Department

Composition and function in AB{sub 5} hydride electrodes

Description: Multicomponent AB, hydrides are attractive replacements for the cadmium electrode in nickel - cadmium batteries. This paper is concerned with the differential effects of Ni substitution by cobalt, Mn and Al upon electrode corrosion and capacity, using alloys having the generic composition of Al(NiCoMnAl){sub 5} and similar to those used for the preparation of commercial battery electrodes. The corrosion of metal hydride electrodes is determined by two factors, surface passivation due to the presence of surface oxides or hydroxides and crystal lattice expansion - contraction the charge - discharge process. Thus, in addition to determining the effects of Ni substitution we will also address the question of whether an observed change is due to a change lattice expansion or to a change in surface passivation, e.g. the formation a corrosion resistant oxide layer.
Date: December 31, 1996
Creator: Adzic, G.D.; Johnson, J.R.; Mukerjee, S.; McBreen, J. & Reilly, J.J.
Partner: UNT Libraries Government Documents Department

Corrosion of AB{sub 5} metal hydride electrodes

Description: Metal hydride electrodes are an attractive substitute for the cadmium electrode in Cd/Ni batteries because of their relatively benign environmental impact and higher energy density. However, even though MH{sub x}/Ni batteries are currently competitive in certain applications, their full potential as cheap, reliable, energy storage devices is not yet realized: a severe penalty has been incurred in storage capacity and materials costs in order to inhibit corrosion and attain acceptable electrode cycle life. Currently there are two types of alloys which are useful as metal hydride electrodes, the AB{sub 5} and the AB{sub 2} classes of intermetallic compounds. Commercial AB{sub 5} electrodes use mischmetal, a low cost combination of rare earth elements. The B{sub 5} component remains primarily Ni but is substituted in part with Co, Mn, Al etc. The partial substitution of Ni increases thermodynamic stability of the hydride phase and corrosion resistance. Such an alloy is commonly written as MmB{sub 5} where Mm represents the mischmetal component; the B{sub 5} composition in commercial batteries is variable but electrodes consisting of MmNi{sub 3.55}Co{sub .75}Mn{sub .4}Al{sub .3} have good storage capacity and cycle life and most AB{sub 5} battery electrodes have a similar composition. The authors have been concerned with the function that individual components play in such an alloy with respect to lattice expansion, hydride stability, and surface passivation. Thus they have focused on the properties of a similar alloy, A(NiCoMnAl){sub 5} where A is La or La{sub 1{minus}x}Ce{sub x}. Some of their results noted here have previously appeared in separate publications; the purpose of this paper is to combine them with new data to give a more coherent and complete whole.
Date: November 1, 1997
Creator: Adzic, G.D.; Johnson, J.R.; Mukerjee, S.; McBreen, J. & Reilly, J.J.
Partner: UNT Libraries Government Documents Department

Synthesis and studies of boron based anion receptors and their use in non-aqueous electrolytes for lithium batteries

Description: A new family of anion receptors based on boron compounds has been synthesized. These compounds can be used as anion receptors in lithium battery electrolytes and can greatly increase solubility and ionic conductivities of various lithium salts, such as LiF, LiCl, CF{sub 3}COOLi and C{sub 2}F{sub 5}COOLi, in DME solutions. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy studies show that Cl{sup {minus}} anions of LiCl are complexed with these compounds in DME solutions. The electrochemical stability of lithium salts and one of the boron compounds in deferent solvents was studied. For the first time, LiF has been successfully used as conducting salt in a novel electrolyte with this boron compound as an additive in DME. A rechargeable Li/LiMn{sub 2}O{sub 4} cell using this electrolyte was successfully cycled 51 times. However, the capacity fades with cycling due to decomposition of the solvent. The cycling performance of the battery was greatly improved by replacing DME with PC-EC-DMC as the solvent.
Date: December 31, 1998
Creator: Sun, X.; Yang, X.Q.; Lee, H.S.; McBreen, J. & Choi, L.S.
Partner: UNT Libraries Government Documents Department

Comparative Studies of the Electrochemical and Thermal Stability of Composite Electrolytes for Lithium Battery Using Two Types of Boron-Based Anion Receptors

Description: Comparative studies were done on two new types of boron based anion receptors, tris(pentafluorophenyl) borane (TFPB) and tris(pentafluorophenyl) borate (TFPBO), regarding conductivity enhancement electrochemical and thermal stability when used as additives in composite electrolytes for lithium batteries. Both additives enhance the ionic conductivity of electrolytes of simple lithium salts, LiF, CF{sub 3}CO{sub 2}Li and C{sub 2}F{sub 5}CO{sub 2}Li in several organic solvents. The electrochemical windows of TPFB based electrolytes in ethylene carbonate (EC)-propylene carbonate (PC)-dmethyl carbonate (DMC) (1:1:3, v/v) are up to 5, 4.76 and 4.96 V for LiF, CF{sub 3}CO{sub 2}Li and C{sub 2}F{sub 5}CO{sub 2}Li respectively. TPFBO has lower electrochemical stability compared to TPFB. The thermal stability of pure TFPB is better than TFPBO. The lithium salt complexes have higher thermal stability than these two compounds. TPFB based electrolytes showed high cycling efficiencies and good cycleability when they were tested in Li/LiMn{sub 2}O{sub 4} cells. The capacity retention of the cells using TFPB based electrolytes during multiple cycling is better than those using TFPBO based electrolytes.
Date: October 17, 1999
Creator: Yang, X. Q.; Lee, H. S.; Sun, X. & McBreen, J.
Partner: UNT Libraries Government Documents Department

New Polymer and Liquid Electrolytes for Lithium Batteries

Description: All non-aqueous lithium battery electrolytes are Lewis bases that interact with cations. Unlike water, they don't interact with anions. The result is a high degree of ion pairing and the formation of triplets and higher aggregates. This decreases the conductivity and the lithium ion transference and results in polarization losses in batteries. Approaches that have been used to increase ion dissociation in PEO based electrolytes are the use of salts with low lattice energy, the addition of polar plasticizers to the polymer, and the addition of cation completing agents such as crown ethers or cryptands. Complexing of the anions is a more promising approach since it should increase both ion dissociation and the lithium transference. At Brookhaven National Laboratory (BNL) we have synthesized two new families of neutral anion completing agents, each based on Lewis acid centers. One is based on electron deficient nitrogen sites on substituted aza-ethers, wherein the hydrogen on the nitrogen is replaced by electron withdrawing groups such as CF{sub 3}SO{sub 3{sup -}}. The other is based on electron deficient boron sites on borane or borate compounds with various fluorinated aryl or alkyl groups. Some of the borane based anion receptors can promote the dissolution of LiF in several solvents. Several of these compounds, when added in equivalent amounts, produce 1.2M LiF solutions in DME, an increase in volubility of LiF by six orders of magnitude. Some of these LiF electrolytes have conductivities as high as 6 x 10{sup -3} Scm{sup -1}. The LiF electrolytes with borane anion acceptors in PC:EC:DEC solvents have excellent electrochemical stability. This has been demonstrated in small Li/LiMn{sub 2}O{sub 4} cells.
Date: March 29, 1999
Creator: McBreen, J.; Lee, H. S.; Yang, X. Q. & Sun, X.
Partner: UNT Libraries Government Documents Department

In situ X-Ray Absorption Spectro-Electrochemical Study of Amorphous Tin-Based Composite Oxide Material

Description: We have measured the XAFS spectra of a sample of tin-based composite oxide (TCO) material with a nominal composition of Sn{sub 1.0}B{sub 0.56}P{sub 0.40}Al{sub 0.42}O{sub 3.47} during the discharge and charge cycles in an ''in situ'' configuration. Our results confirm the amorphous nature of TCO and show that Sn in TCO is coordinated with 3 oxygen atoms at a distance of 2.12 {angstrom}. Upon discharging, initially, Li interacts with the electrochemically active Sn-O center forming metallic Sn in the form of clusters containing just a few atoms. Upon further discharge, Li alloys with Sn forming initially highly dispersed forms of Li{sub 2}Sn{sub 5} and/or LiSn and then Li{sub 7}Sn{sub 3}, Li{sub 5}Sn{sub 2}, Li{sub 13}Sn{sub 5}, or Li{sub 7}Sn{sub 2}. The true nature of the formed alloys could be significantly different from that of the corresponding crystalline phases. Upon charging, metallic Sn is produced with a Sn-Sn distance intermediate to those of gray and white Sn.
Date: November 1, 1998
Creator: Mansour, A. N.; Mukerjee, S.; Yang, X. Q. & McBreen, J.
Partner: UNT Libraries Government Documents Department

In Situ Synchrotron X-Ray Techniques for the Study of Lithium Battery Materials

Description: The combination of in situ X-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) is a very powerful technique in the study of lithium battery cathode materials. XRD identifies the phase changes that occur during cycling and XAS gives information on the redox charge compensation processes that occur on the transition metal oxides. Because of its element specific nature XAS can identify the occurrence of redox processes on the various cations in doped oxide cathode materials. Since XAS probes short range order and is particularly useful in the study of amorphous tin based composite oxide anode materials.
Date: November 1, 1998
Creator: McBreen, J.; Mukerjee, S.; Yang, X. Q. & Sun, X., Ein-Eli, Y.
Partner: UNT Libraries Government Documents Department

In Situ XAS and XRD Studies of Substituted Spinel Lithium Manganese Oxides in the 4-5 V Region

Description: Partial substitution of Mn in lithium manganese oxide spinel materials by Cu and Ni greatly affects the electrochemistry and the phase behavior of the cathode. Substitution with either metal or with a combination of both shortens the 4.2 V plateau and results in higher voltage plateaus. In situ x-ray absorption (XAS) studies indicate that the higher voltage plateaus are related to redox processes on the substituents. In situ x-ray diffraction (XRD) on LiCu{sub 0.5}Mn{sub 1.5}O{sub 4} shows single phase behavior during the charge and discharge process. Three phases are observed for LiNi{sub 0.5}Mn{sub 1.5}O{sub 4} and two phases are observed in the case of LiNi{sub 0.25}Cu{sub 0.25}Mn{sub 1.5}O{sub 4}. The electrolyte stability is dependent on both the operating voltage and the cathode composition. Even though Ni substituted materials have lower voltages, the electrolyte is more stable in cells with the Cu substituted materials.
Date: November 1, 1998
Creator: McBreen, J.; Mukerjee, S.; Yang, X. Q.; Sun, X. & Ein-Eli, Y.
Partner: UNT Libraries Government Documents Department

Investigation of the electrocatalysis for oxygen reduction reaction by Pt and binary Pt alloys: an XRD, XAS and electrochemical study

Description: Electrocatalysis for the oxygen reduction reaction (ORR) on five binary Pt alloy electrocatalysts (PtCr/C, PtMn/C, PtFe/C, PtCo/C and PtNi/C) supported on carbon have been investigated. The electrochemical characteristics for ORR in a proton conducting fuel cell environment has been correlated with the electronic and structural parameters determined under in situ conditions using XANES and EXAFS technique respectively. Results indicate that all the alloys possess higher Pt 5d band vacancies as compared to Pt/C. There is also evidence of lattice contraction in the alloys (supported by XRD results). Further, the Pt/C shows increase in Pt 5 d band vacancies during potential transitions from 0.54 to 0.84 V vs. RHE, which has been ration@ on the basis of OH type adsorption. In contrast to this, the alloys do not exhibit such an enhancement. Detailed EXAFS analysis supports the presence of OH species on Pt/C and its relative absence in the alloys. Correlation of the electrochemical results with bond distances and d-band vacancies show a volcano type behavior with the PtCr/C on top of the curve.
Date: December 31, 1995
Creator: Mukerjee, S.; McBreen, J. & Srinivasan, S.
Partner: UNT Libraries Government Documents Department

Polymer electrolytes for a rechargeable li-Ion battery

Description: Lithium-ion polymer electrolyte battery technology is attractive for many consumer and military applications. A Li{sub x}C/Li{sub y}Mn{sub 2}O{sub 4} battery system incorporating a polymer electrolyte separator base on novel Li-imide salts is being developed under sponsorship of US Army Research Laboratory (Fort Monmouth NJ). This paper reports on work currently in progress on synthesis of Li-imide salts, polymer electrolyte films incorporating these salts, and development of electrodes and cells. A number of Li salts have been synthesized and characterized. These salts appear to have good voltaic stability. PVDF polymer gel electrolytes based on these salts have exhibited conductivities in the range 10{sup -4} to 10{sub -3} S/cm.
Date: October 1, 1996
Creator: Argade, S.D.; Saraswat, A.K.; Rao, B.M.L.; Lee, H.S.; Xiang, C.L. & McBreen, J.
Partner: UNT Libraries Government Documents Department

Effect of Ce composition on the structural and electronic characteristics of some metal hydride electrodes: A XANES and EXAFS investigation

Description: Substitution of the B component in the prototype AB{sub 5} type (LaNi{sub 5}) metal hydride alloys have resulted in their increased acceptance as anodes for rechargeable alkaline batteries. Recently substitution of the A component (La) for imparting properties such as increased corrosion resistance has received attention. This investigation deals with the role of Ce as a substituent for the La and its effect in terms of corrosion resistance. The alloys chosen have the general composition of La{sub x}Ce{sub 1-x}B{sub 5} (x = 1, 0.8, 0.5 and 0.25) where B is Ni{sub 3.55}CO{sub 0.75}Mn{sub 0.4}Al{sub 0.3} together with alloys containing the mischmetal (Mm) as the A component (both synthetic and commercial). Electrochemical cycling results show that Ce lowers the capacity loss in the alloys and that this effect is not a simple function of the extent of lattice expansion during hydriding as was previously suggested. Correlation of the electrochemical and XAS results show that capacity loss is directly related to the extent of Ni corrosion. Effect of Ce substitution seems to result in a stable Ce oxide hydroxide coating which imparts the corrosion resistance.
Date: December 31, 1994
Creator: Mukerjee, S.; McBreen, J.; Reilly, J.J.; Johnson, J.R.; Adzic, G.; Kumar, M.P.S. et al.
Partner: UNT Libraries Government Documents Department

Reaction kinetics and x-ray absorption spectroscopy studies of yttrium containing metal hydride electrodes

Description: This was a study of electrode degradation mechanisms and the reaction kinetics of LaNi{sub 4.7}Sn{sub 0.3}, La{sub (1{minus}x)} Y{sub x}Ni{sub 4.7}Sn{sub 0.3} (x = 0.1, 0.2, and 0.3) and La{sub 0.7}Y{sub 0.3}Ni{sub 4.6}Sn{sub 0.3}Co{sub 0.1} metal hydride electrodes. Alloy characterization included x-ray diffraction (XRD), x-ray absorption (XAS), hydrogen absorption in a Sieverts apparatus, and electrochemical cycling of alloy electrodes. The atomic volume of H was determined for two of the alloys. Electrochemical kinetic measurements were made using steady state galvanostatic measurements, galvanodynamic sweep, and electrochemical impedance techniques. XAS was used to examine the degree of corrosion of the alloys with cycling. Alloying with Y decreased the corrosion rate. The results are consistent with corrosion inhibition by a Y containing passive film. The increase in the kinetics of the hydrogen oxidation reaction (HOR) with increasing depth of discharge was much greater on the Y containing alloys. This may be due to the dehydriding of the catalytic species on the surface of the metal hydride particles.
Date: December 31, 1998
Creator: Ticianelli, E.A.; Mukerjee, S.; McBreen, J.; Adzic, G.D.; Johnson, J.R. & Reilly, J.J.
Partner: UNT Libraries Government Documents Department

An XAS investigation of corrosion characteristics in AB{sub 5} type metal hydride electrodes

Description: Apart from the stress cracking due to lattice expansion and contraction during cycling, several substituents such as Ce and Co, and additions to the electrolyte such as ZnO have the ability to significantly improve the cycle life and corrosion characteristics in AB5 type metal hydride alloys. In situ XANES and SVET studies reveal that Ce substitution causes a protective passivation layer comprising of Ce oxides. This significantly reduces the extent of corrosion of substituents such as Ni despite greater percent volume expansion and contraction cycle compared with non Ce substituted samples. The Co substitution reduces the extent of percent volume expansion in the lattice cycle and hence the extent of stress cracking. It also segregates to the surface as Co(OH)2 which due to its higher conductivity counters the resistive effects due to build up of surface Ni(OH)2. Addition of ZnO to the electrolyte suppresses corrosion of substituents such as Ni in non Ce substituted alloys resulting in improved cycle life. The effects on Ce substituted alloys is negligible.
Date: August 1, 1997
Creator: Mukerjee, S.; McBreen, J.; Reilly, J.J.; Johnson, J.R.; Adzic, G.D. & Marrero, M.R.
Partner: UNT Libraries Government Documents Department

Ion pair dissociation effects of aza-based anion receptors on lithium salts in polymer electrolytes

Description: The addition of aza-based anion receptors greatly increases the conductivity of polymer electrolytes based on LiCl and KI complexes with poly(ethylene oxide) (PEO). In some cases the conductivity increase is more than two orders of magnitude. Also the addition of the anion acceptors imparts a rubber like consistency to the normally stiff PEO salt films. Ion-ion, ion-polymer and anion-complex interactions were studied using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the K and Cl K edges and at the I L{sub I} edge. The NEXAFS results show that Cl{sup {minus}} and I{sup {minus}} anions are complexed with the nitrogen groups of the anion receptors. The degree of complexation is related the chain length of the complexing agent and the number of R{double_bond}CF{sub 3}SO{sub 2} groups that are used to substitute for the amine hydrogen atoms in these aza-ether compounds. NEXAFS spectra at potassium K edge provide supplemental evidence for the ion pair dissociation effects of the anion receptors. The results show that dissociated K{sup +} cations are complexed with oxygen atoms of the PEO chains.
Date: December 31, 1996
Creator: Yang, X.Q.; Lee, H.S.; Xiang, C.; McBreen, J.; Choi, L.S. & Okamoto, Y.
Partner: UNT Libraries Government Documents Department

In situ x-ray diffraction studies of a new LiMg{sub 0.125}Ni{sub 0.75}O{sub 2} cathode material

Description: A Synchrotron x-ray source was used for In Situ x-ray diffraction studies during charge on a new LiMg{sub 0.125}Ti{sub 0.125}Ni{sub 0.75} cathode material synthesized by FMC Corp. It had been demonstrated by Gao that this new material has superior thermal stability than LiNiO{sub 2} and LiCo{sub 0.2}Ni{sub 0.8}O{sub 2} at over-charged state. In this current paper, studies on the relationship between the structural changes and thermal stability at over-charged state for these materials are presented. For the first time, the thermal stability of these materials are related to their structural changes during charge, especially to the formation and lattice constant change of a hexagonal phase (H3). The spectral evidence support the hypothesis that the improvement of thermal stability is obtained by suppressing the formation of H3 phase and reducing the shrinkage of its lattice constant c when charged above 4.3 V.
Date: July 1, 1999
Creator: Yang, X.Q.; Sun, X.; McBreen, J.; Gao, Y.; Yakovleva, M.V.; Xing, X.K. et al.
Partner: UNT Libraries Government Documents Department