1998 MRS Fall Meeting & Exhibit

Chairs

Christian Julien, Univ Pierre et Marie Curie 
Gholam-Abbas Nazri, GM NAO R&D Center

Symposium Support 

• Lawrence Berkeley National Laboratory
• U.S. Department of Energy 

* Invited paper

SESSION EE1: CATHODE MATERIALS FOR ADVANCED BATTERIES 
Chairs: Gholam-Abbas Nazri and Jean-Marie Tarascon 
Monday Morning, November 30, 1998 
Constitution (S)

8:30 AM *EE1.1 
SUPERCAPACITORS AND BATTERIES. J.B. Goodenough , V. Manivannan, and Hee Y. Lee, Texas Material Institute, University of Texas at Austin, Austin, TX. 

Design criteria for the cathode of a rechargeable battery are compared with those for the electrodes of a supercapacitor. Chemical tuning of redox energies is a critical consideration for both applications, and some tuning principles will be discussed. The brannerite and NASICON structures offer high-power battery-cathode hosts; the former has a voltage limitation, the latter a capacity limitation. Supercapacitor electrodes may be identical after discharge, as in the case of amorphous RuOOHnH₂O, but they may also have different chemical compositions. Some preliminary supercapacitor data will be presented. 

9:00 AM *EE1.2 
INTERCALATION IN LITHIUM-METAL OXIDES: FIRST-PRINCIPLES MODELING TO UNDERSTAND PHASE STABILITY AND ELECTROCHEMICAL PROPERTIES. G. Ceder , Massachusetts Institute of Technology, Department of Materials Science and Engineering, Cambridge MA. 

Many of the properties of insertion electrodes can be directly computed with first-principles methods. Such computations are solely based on the basic laws of Physics and therefore require no experimental data. This makes them particularly suitable for predicting the properties of novel or incompletely characterized materials. We have recently demonstrated the applicability of first-principles methods to predict the Li-insertion potential and the phase stability in lithium-metal oxides [1-3]. This has already been used to predict the insertion behavior of previously untested compounds[4]. We present first-principles results for the phase stability in the Li_xCoO₂ and Li_xMnO₂ systems. In Li_xCoO₂ we predict the occurence of ''staging'' at low Li concentrations. Calculations are also highly effective instyding the electronic changes that occur in the material upon lithiation. While Li insertion in LixCoO2 transfer an extra electron to the t_2g band of the material we find that the net-electron increase is largely located around the oxygen ions. This is due to the increased ionicity of the cobalt-oxygen bond upon lithiation. We demonstrate how this effect relates to important cathode properties such as the average lithiation voltage and the variation of lattice constant with Li content. 

9:30 AM *EE1.3 
INTERCALATE AGGREGATION AND NLO PROPERTIES OF INTERCALATED LAMELLAR CHALCOGENO PHOSPHATE LATTICES. Rene Clement, Thibaud Coradin, Laboratoire de Chimie Inorganique, Univ de Paris-Sud, Orsay, FRANCE; Anthony Francis , Jennifer Holt, Dept of Chemistry, Univ of Michigan, Ann Arbor, MI. 

The transition metal chalcogeno-phosphates form a family of broad band-gap, p-type semiconductors that crystallize in highly anisotropic 2D structures. The archetypal structure consists of a plane of octahedrally coordinated transition metal ions (M) sandwiched between sheets of chalcogen atoms (X). The three dimensional structure is generated by a stacking arrangement secured by van der Waal's interactions between the adjacent chalcogen atom layers. The lability of the dipositive 1st-row transition metal cations and the availability of low-energy interlamellar sites facilitates a solid-state cation exchange reaction. As guest cations enter the interlamellar interstices from solution, lattice cations are displaced from the lamella creating mobile lattice vacancies. The low energy required to create this characteristic defect is essential to the facile cation exchange chemistry of the MPS₃ lattices. 
After intercalation, fully 25% of the lattice cation sites may be vacant. The structure, mobility and organization of vacancies in MPX₃ materials profoundly affect the properties of these 2D materials and distinguish their solid-state chemistry from that of 3D solids. The diffusion of vacancies and interstitials leads to the formation of vacancy and interstitial aggregates or superlattices that affect the dielectric and magnetic behavior of these materials. 
Intercalation compounds of MPS₃ lattices with dipolar molecular cations exhibit high efficiency optical second harmonic generation (SHG). This is unexpected since the native MPS₃ materials crystallize in centrosymmetric crystal lattices. The SHG may result from spontaneous spatial organization of the intercalate. For efficient SHG, spatial organization must have a characteristic length scale on the order of the second harmonic wavelength, or about 1 micron. We have carried out extensive spectroscopic and magnetic resonance studies of vacancy diffusion and intercalate aggregation in these materials. 

10:30 AM *EE1.4 
HYDROTHERMAL SYNTHESIS AND ELECTROCHEMICQAL PROPERTIES OF LAYERED VANADATES. Jacques Livage ¹, Laure Bouhedja¹, Socorro Castro-Garcia¹, Christian Julien². ¹Chimie de la Matière Condensée and ²Milieux Désordonnés et Hétérogénes, Université Pierre et Marie Curie, Paris, FRANCE. 

The hydrothermal synthesis of vanadates leads to a large variety of crystalline materials. The nature of the molecular precursor mainly depends on pH, but the way these precursors condense to give a solid phase can be controlled by other ions in the solution. Layered structure are formed around pH=6 where negatively charged species such as [VO(OH)₄(OH₂)]^-should behave as precursors. Condensation occurs via V-OH groups in the equatorial plane leading to layered structures in which cations are inserted between the vanadate planes. Fibrous crystals of NaV₃O₈,H₂O are obtained from a mixture of V₂O₅ and NaOH. Some reduction may also occur when organic cations such as tetramethyl ammonium N(CH₃)₄]⁺ (TMA) are used leading to mixed valence vanadates, (TMA)₄V₄O₁₀, TMAV₃O₇ or TMAV₈O₂₀. The mixed valence -Na_xV₂O₅ bronze is obtained in the presence of Na⁺ and (TMA)⁺. It has a layered structure close to that of V₂O₅ with mixed Na⁺ ions inserted between valence [V₂O₅]^- planes. 
This paper discusses the chemical mechanisms involved in the formation of these layered vanadate phases and describes their electrochemical properties. Hydrothermal syntheses often lead to fibrous crystals. Such a morphology appears to improve diffusion processes at the electrode-electrolyte interface. Discharge curves show that up to one Li⁺ ion per vanadium can be reversibly inserted in -Na_xV₂O₅. This compound is already well known for its low temperature spin-Peierls transition but its potential use as secondary cathode in lithium batteries has never been pointed out. 

11:00 AM *EE1.5 
SYNTHESIS OF MANGANESE AND VANADIUM OXIDES AS CATHODES FOR LITHIUM BATTERIES. M. Stanley Whittingham , Materials Research Center and Chemistry Department, State University of New York at Binghamton, Binghamton, NY. 

The limitation to presently available lithium batteries is the relatively low capacity of the cathode, so that cells such as Li/cobalt oxide have no higher an energy density than the original sulfide cells based on titanium. Much effort is therefore being targeted at cathodes where one lithium can be reversibly stored per transition metal. Our research is aimed at synthesizing new transition metal oxides that meet this target, using predominantly soft chemistry approaches such as solvothermal, ion-exchange and intercalation. Recent results for vanadium oxides and alkali manganese oxides will be described. For the former, systematic studies have been made of the effect of pH, acid, the organic template/reducing agent, organic content, and vanadium oxidation state on the structure and electrochemical behavior. For the latter, close to 1 Li/Mn can be cycled, but there is a degradation of the ordered layered structure on cycling toward the spinel lattice. Both soft chemistry and high temperature approaches for diminishing the Mn diffusion by pillaring the lattice will be described. Supported by DOE (Office of Transportation Technologies) and NSF-DMR. 

11:30 AM EE1.6 MOLYBDENUM AND VANADIUM OXIDE POLYCRYSTALLINE FILMS. PROPERTIES AND APPLICATION TO LITHIUM MICROBATTERIES. B. Yebka , L. El-Farh, C. Julien, Laboratoire des Milieux Desordonnes et Heterogenes, Universite Pierre et Marie Curie, Paris, France; G.A. Nazri, Physics and Physical Chemistry Department, RCEL, General Motors R&D Center, Warren, MI. 

We report on the growth of flash-evaporated MoO3 and V2O5 films and their application as positive electrodes in lithium microbatteries. We have characterized various polycrystalline samples and studied how their structural and electrical properties are affected by the different preparation conditions. The highest quality films were grown on silicon substrate maintained at 250C and annealed at 300C. It is shown that the growth conditions play an important role in the electrochemical properties of the film. Both thermodynamics and kinetics are strongly dependent on the film morphology. Microbatteries fabricated with cathodes formed at moderate temperature show a volumetric capacity 80 A h/m/cm2. The cells exhibit a monotonous discharge profile indicating that the cathode materials remain in the single phase even for a large degree of intercalation. 

SESSION EE2: CATHODE MATERIALS FOR ADVANCED BATTERIES 
Chairs: Christian Julien and Stanley Whittingham 
Monday Afternoon, November 30, 1998 
Constitution (S)

1:30 PM *EE2.1 EFFECT OF Bi SPECIES ON THE MnO₂-TYPE PHASES OBTAINED FROM LiMn₂O₄ IN AQUEOUS ACIDIC MEDIA. D. Larcher, P. Courjal, A. Blyr, A. du Pasquier, G. Amatucci^*, and J-M Tarascon, Laboratoire de Reactivite et Chimie des Solides, Universite de Picardie Jules Verne, Amiens, FRANCE ^*Bellcore, NJ. 
The nature of the phases obtained at room temperature and 95 ƒC by acid digestion of LiMn₂O₄ phases prepared was investigated. The transformation from -MnO₂ to -/-MnO₂ observed when LiMn₂O₄ is treated in H₂SO₄ aqueous solution (2.5 M) at 95 ƒC was found to be the result of a dissolution-crystallization mechanism involving 1) a delithiation process leading to -MnO₂ 2) a progressive dissolution of -MnO₂, and 3) a surface oxidation of the dissolved Mn²⁺ species to form the -/-MnO₂ phases. We found that -/-MnO₂ precipitation can be strongly modified with the addition of a soluble Bi³⁺ salt in the reaction media with the kinetics of this transformation depending on the amount of added salt. Furthermore, we demonstrated that some Bi species are chemically adsorbed at the surface of the -MnO₂ oxide. Based on these observations the mechanism to account for the role of Bi in modifying the -MnO₂ to -/-MnO₂ phase transformation will be proposed. The relevance of such findings with respect to the optimization of the LiMn₂O₄/C Li-ion system will be discussed. 

2:00 PM *EE2.2 
ELECTROCHEMICAL AND PHYSICAL STUDY OF LiMn₂O₄ BASED DEFECT SPINELS. Yves Chabre , Universite Joseph Fourier, Grenoble, FRANCE; Rosa Palacin, ICMAB (CSIC), Bellatera, SPAIN; Glenn G. Amatucci, Bellecore, Red Bank, NJ; Michel Anne, Pierre Strobel, CNRS, Grenoble, FRANCE; Michel Menetrier, ICMCB, Universite de Bordeaux, FRANCE; Jean-Marie Tarascon, Universite de Picardie, Amiens, FRANCE. 

The LiMn₂O₄ spinel phase has been given intensive studies for years as positive electrode material for Li-ion batteries, due to its reversible Li deintercalation in the 4.0-4.15 V potential range. But when prepared with some specific conditions (heat treatment temperature, quenching or slow cooling, etc..) this compound was shown to present a reversible redox step at 4.5 V as well as a reduction step at 3.3 V, both appearing to the expense of the 4.0-4.15 V one. These states have attracted attention because they correspond to electrode materials with lower cycling performances. Tarascon et al. suggested that the 4.5 V step is related to Li-Mn cation mixing with Mn³⁺ in tetrahedral sites, whereas Gao and Dahn gave evidence that the presence of the 3.3V reduction step is related to that of the 4.5 V redox one, and that their amplitude are related to the amount of oxygen deficiency. An intriguing question is the occurence of these states for both manganese oxide spinels given as cation defective, i.e. LiMn₂O₄ with x < 1, and manganese oxifluoride spinels LiMn₂O_4-yF_y, i.e. anion defective ones. We will present in this paper results of an extensive study undertaken for determining the physico-chemical origin of these states. This includes electrochemical, chemical, thermal, XRD and NMR measurements on several heat treated Li_xMn₂O₄, and also on a partly (y = 0.26) fluorinated sample. The main results deals with a) PITT determination of the oxidation potential of the 3.3 V reduction, which appears to occur with a large hysteresis; b) a structural study using high resolution in-situ XRD with synchrotron radiation in transmission mode, which made possible to observe and follows the evolution of satellites and additional lines upon electrochemical cycling; and c) a study of the electrochemical behavior of the system below the temperature of the cubic to tetragonal distorsion which is know to occur close to room temperature in these defect spinels. We will present and discuss all these observations which lead us to assign both the 3.3 

2:30 PM EE2.3 
FIRST-PRINCIPLES CALCULATIONS FOR LITHIATED MANGANESE OXIDES. R. Prasad, R. Benedek , M.M. Thackeray, Argonne National Laboratory, Argonne, IL; J.M. Wills, Los Alamos National Laboratory, Los Alamos, NM. 

The judicious introduction of dopants is a fruitful strategy for tuning the performance of Li battery cathodes, for example by enhancing structural stability. First principles theory can assist in the search for appropriate additives if sufficient accuracy in predictions of relative energies of different phases (with and without dopants) can be achieved. Calculations with the full-potential linearized muffin-tin orbital (FP-LMTO) method will be presented for lithiated manganese dioxides. The Li_xMnO₂compounds under investigation have layered-type, spinel-type and hollandite-type structures with different crystallographic symmetries, e.g., monoclinic, orthorhombic, tetragonal, rhombohedral and cubic. Mn atoms have a strongly magnetic character, which must be incorporated in a realistic treatment. Our calculations address relatively small unit cell antiferromagnetic atomic configurations, which represent at least reasonable approximants to the ground state configurations. Magnetic neutron diffraction measurements are available only for the orthorhombic structure. Calculated densities of electronic states for all systems show the Mn d-band near the Fermi edge, above the O-2p band. The magnetic moment varies from system to system. This behavior is in contrast with recent Hartree-Fock calculations by Mackrodt and Williamson, which show the occupied part of the Mn-d band below the O-2p band. 

3:30 PM *EE2.4 
MANGANESE DIOXIDES: CHEMICAL-STRUCTURAL DISORDER, ELECTRONIC PROPERTIES, ELECTROCHEMICAL ACTIVITY AND PROTON REVERSIBLE INSERTION. Christiane Poinsignon , Laboratoire d'Electrochimie, de Physicochimie des Materiaux et des Interfaces, CNRS-INP, Grenoble, FRANCE. 

The synthetic battery active manganese dioxides (MD) are disordered materials who's electrochemical activity is due to the presence of structural disorder associated to chemical defects induced by the synthesis conditions and evidenced in the chemical formula defined by Ruetschi. Analysis of their XRD pattern was performed thanks to intergrowth (Pr) and microtwinning (Tw) defects, associated respectivelly to the presence of Mn3+ and manganese vacancies. A classification of these dioxides in terms of increasing rate of Pr and Tw gives account for their increasing electrochemical activity deduced from the analysis of the reduction voltamograms in 1N KOH. Their IR spectra exhibit OH bending modes of increasing width with increasing defects rate. Each type of defect induces a modification of the electronic properties making the Fermi energy level to decrease then the electrode potential to increase as well as the reduction kinetics. The semi-conducting properties of these samples confirm the influence of the defects on the conductivity. The activation energy of conductivity gives access to the width of the gap which varies as the inverse of the electrochemical activity: the semi-metallic behavior of beta-MD is confirmed. The kinetics study by Impedance spectroscopy of the MD reversible reduction in 1N KOH provides a direct measurement of the proton diffusivity for each reduction rate. 

4:00 PM EE2.5 
DIRECT OBSERVATION OF ELECTROCHEMICAL CYCLING INDUCED DAMAGE IN LITHIUM BATTERY CATHODES. Haifeng Wang , Young-Il Jang, Biying Huang, Yet-Ming Chiang and Donald R. Sadoway, Massachusetts Institute of Technology, Department of Materials Science and Engineering, Cambridge, MA. 

Lithium transition metal oxides used as intercalation electrodes for rechargeable lithium batteries are widely studied in search of structural stability and improved electrochemical performance. In this study we show that even LiCoO₂, considered to be amongst the most stable in the layered rock-salt structure (-NaFeO₂), is irreversibly damaged by repeated electrochemical cycling. We used high temperature processed LiCoO₂ powders to make test cells for electrochemical testing. Tests resulted in little capacity fade over 50 cycles (130 mAh/g, 2.5-4.35 V), and bulk X-ray diffraction (XRD) did not show any apparent structural transformation. However, direct observation at the particle scale using TEM and structural simulations revealed severe damage to the individual particles in the form of crystallographic defects and cation disorder. Also reported will be observations in the LiMnO₂ system, where aluminum doping has been shown to stabilize the monoclinic phase [Y.-I. Jang et al., Electrochem. Solid-State Lett., 1998] and improve the capacity retention at elevated temperatures. 

4:30 PM *EE2.6 
THIN FILMS OF IONIC CONDUCTORS BY LASER ABLATION. M. Morcrette, P. Barboux , J. P. Boilot, Physique de la Matiere Condensee, Ecole Polytechnique, Paris, FRANCE. 

Laser ablation was used to deposit thin films of insertion compounds and solid state electrolytes for studies in the domain of electrochemical ion and gas sensors. Lithium conducting materials such as lisicon phosphates and perovskites (in the Li-La-Ti-O system) as well as complex lithium transition metal oxides (LiMO where M is a transition metal Co, Ni, Mn) have been deposited. The chemical composition in the films has been studied by Rutherford Backscattering spectrometry and nuclear activation reactions in the case of the light elements (O, Li). At low oxygen pressures, a large loss of the light elements (Li, P, O) is generally observed. But this loss may have different origins. In the case of lisicon (LiTi (PO )), phosphorus species are scattered by collisions in the laser plasma. In the case of lithium transition metal oxides (LiMO), the oxygen and lithium contents are determined by a thermodynamical equilibrium between the films and the partial pressures in the chamber. In these cases, laser ablation allows the synthesis of crystalline structures with a large range of oxygen non stoichiometry as compared to solid state reactions. They lead to interesting electrical properties. Using the appropriate temperatures and oxygen pressures, films with the correct stoichiometry could be obtained as polycrystalline onto Si or Si/Pt substrates whereas they exhibit high texturing and epitaxial growth onto MgO or MgO/Pt. We have used the films of LiMnO and LiCoO as electrochemical sensors for measurement of the concentration of lithium in solutions. They show a very rapid and selective response. 

SESSION EE3: POSTER SESSION 
Chairs: Christian Julien, Gholam-Abbas Nazri and Aline D. Rougier 
Monday Evening, November 30, 1998 
8:00 P.M. 
Grand Ballroom (S)

EE3.1 
FLUORINE-SUBSTITUTED BISMUTH-CONTAINING OXIDE SUPERCONDUCTORS AS ELECTRODE MATERIALS. Gennady S. Petrov , Leonid A. Bashkirov and Andrew I. Clyndyuck, Belarus State Technol Univ, Dept of Phys and Col Chem, Minsk, BELARUS. 

A great majority of studies of high-temperature superconductors known was made below room temperature. But these compounds, having high non-ionic electrical conduction, are considered as perspective electrode materials in high-temperature electrochemical devices of different types. However physicochemical investigations of HTS phases above room temperature are scarce, in spite of physicochemical data for these materials are valuable in many practical and theoretical fields. Aim of our paper is synthesis and study of thermal expansion (quartz dilatometer) and DC electrical conductivity (four-probe method) in air above room temperature of HTS-phases Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O_xF_y in the system Bi-Sr-Ca-Cu-O with simultaneous partial substitution of bismuth by lead and of oxygen by fluorine. Samples were prepared from oxides of bismuth, lead, copper, carbonates of strontium, calcium, fluorides of bismuth (sample I) and copper (sample II). For (I) and (II) at 473 - 973 K temperature dependence of relative elongation was close to the linear, here certain divergence of data, obtained for heating and cooling regimes, took place. Calculated values of average linear thermal expansion coefficient were 12.9 x 10^-6 and 14.3 x 10^-6 for K^-1 (I) and (II) respectively. For (I) and (II) up to 600 - 650 K temperature dependencies of electrical resistivity were close to the linear, hysteresis of data for heating cooling cycles was absent. Absence of linear Arrhenius dependencies for conductivity  made it impossible to evaluate energy activation of conduction. In (S cm^-1) values at 300 (900) K were: 5.4 (4.5) and 4.6 (3.8) for (I) and (II) respectively. Note that above properties of (I) and (II) did not change practically after storage in air for three months. The results obtained make it possible to consider (II) and (II) as electrode materials. 

EE3.2 
CONDUCTIVITY OF MIXED OXYFLUORIDES OF RARE-EARTH ELEMENTS. Raida A. Vecher, Lyudmila M. Volodkovich , Alim A. Vecher, Bel State Univ, Dept of Phys Chem, Minsk, BELARUS. 

This paper gives the results of measurements of electrical conduction of a number of mixed oxyfluorides of rare-earth elements La₂Ln₂O₃F₆ (Ln = Nd, Sm, Dy, Yb) as well as La₂NdO₃F₃. All oxyfluorides were prepared by sintering of mixtures La₂O₃ and LnF3 in atmosphere of argon at temperatures 1200-1300 K. X-ray analysis showed that all oxyfluorides La₂Ln₂O₃F₆ had tetragonal symmetry, structure of La₂NdO₃F₃ was rhombohedral. Measurements of AC conductivity (1000 Hz) were made on pressed polycrystalline samples in argon atmosphere, using graphite blocking electrodes. For all oxyfluorides La₂Ln₂O₃F₆ we found kinks on temperature dependences of conductivity, connected with transition to the high-temperature cubic phase. Temperatures (T, K) of reversible phase transition were: 713 (Nd), 734 (Sm), 743 (Dy), 806 (Yb), 837 (La₂NdO₃F₃). The highest conductivity (a) was determined for La₂NdO₃F₃: 
Ig[T/(Scm^-1 )](0.06) = 7.75 - 5.7510³ (1/T), (570-713 K) 
Ig[T/( Scm^-1 )](0.01) = 4.87 - 3.7510³ (1/T), (713-905 K) 
Note that transition of oxyfluorides to the high-temperature modification is accompanied by essential decreasing of energy activation of conductivity down to 0.4-0.8 eV. By measurements of EMF of galvanic elements Cu₂O, Cu  oxyfluoride  CoO, Co and Tubandt method transference number of oxygen ions was evaluated, which was about 0.95-0.99 above 850 K.