Maria Helena Braga

Alternative strategy for a safe rechargeable battery

The advent of a Li+ or Na+ glass electrolyte with a cation conductivity σi > 10−2 S cm−1 at 25 °C and a motional enthalpy ΔHm = 0.06 eV that is wet by a metallic lithium or sodium anode is used to develop a new strategy for an all-solid-state, rechargeable, metal-plating battery. During discharge, a cell plates the metal of an anode of high-energy Fermi level such as lithium or sodium onto a cathode current collector with a low-energy Fermi level; the voltage of the cell may be determined by a cathode redox center having an energy between the Fermi levels of the anode and that of the cathode current collector. This strategy is demonstrated with a solid electrolyte that not only is wet by the metallic anode, but also has a dielectric constant capable of creating a large electric-double-layer capacitance at the two electrode/electrolyte interfaces. The result is a safe, low-cost, lithium or sodium rechargeable battery of high energy density and long cycle life.

Novel Li3ClO based glasses with superionic properties for lithium batteries

Three types of next generation batteries are currently being envisaged among the international community: metal-air batteries, multivalent cation batteries and all-solid-state batteries. These battery designs require high-performance, safe and cost effective electrolytes that are compatible with optimized electrode materials. Solid electrolytes have not yet been extensively employed in commercial batteries as they suffer from poor ionic conduction at acceptable temperatures and insufficient stability with respect to lithium-metal. Here we show a novel type of glasses, which evolve from an antiperovskite structure and that show the highest ionic conductivity ever reported for the Li-ion (25 mS cm−1 at 25 °C). These glassy electrolytes for lithium batteries are inexpensive, light, recyclable, non-flammable and non-toxic. Moreover, they present a wide electrochemical window (higher than 8 V) and thermal stability within the application range of temperatures.

Thermodynamic assessment of the Li-Si system

The Li-Si binary system was thermodynamically assessed using experimental phase diagram and thermodynamic data. Due to inconsistencies in the experimental data, two optimizations were performed. In both cases, the obtained sets of parameters are different and are discussed.

The Cu-Li-Mg system at room temperature

The Cu‐Li‐Mg system still remains very unknown. Mel’nik et al. (Russ. Metall. 3 (1976) 152‐156) studied it at 643 K. They considered the existence of a stoichiometric compound Cu8Li2Mg15 with an orthorhombic structure. In this work, the Cu‐Li‐Mg system was studied at room temperature by means of SEM (scanning electron microscopy) / EDS (energy dispersive spectroscopy) and X-ray diffraction. Results were compared with the ones from (Russ. Metall. 3 (1976) 152‐156) and with the assessments for the binaries Cu‐Li, Cu‐Mg and Li‐Mg present in the literature (COST-507, Thermochemical database for light metal alloys, in: I. Ansara (Ed.), Concerted Action on Materials Sciences, European Commission DGXII Publ., 1994, pp. 132‐134; A.A. Nayeb-Hashemi, J.B. Clark, Phase Diagrams of Binary Magnesium Alloys, ASM International, 1988, pp. 184‐194). # 2000 Elsevier Science B.V. All rights reserved.

New Promising Hydride Based on the Cu-Li-Mg System

We investigated the ternary Cu-Li-Mg system, in particular the CuLixMg2-x (x = 0.08) for hydrogen storage. Instead of crystallizing in an orthorhombic phase, as CuMg2, this phase presents a hexagonal structure very similar to that of NiMg2 and NiMg2H0.3. In this work we will discuss the structure of CuLixMg2-x by the analysis of the neutron scattering data and first principles calculations. The first results for a hydride (deuteride) phase will also mentioned since preliminary studies at LANSCE showed that CuLixMg2-x might absorb approximately 5.3 to 6 wt% of H at an equilibrium pressure of approximately 27 bar at 200 o C. If these results are confirmed in future work, this will mean that, not only CuLixMg2-x absorbs a considerable amount of hydrogen (close to DOEs expectations for hydrogen storage materials), but also will probably release it at a temperature in the range of 50 to 150 o C, where applications are easier to develop. Hence it should be possible to use this alloy with fuel cells or in batteries. Another important observation is that cycling has a strong effect on the structure of the hydride.

HT-XRD in the study of Cu-Li-Mg

In a previous study on Cu-Li-Mg system, the authors of the present paper concluded that the ternary phase in that system corresponds to CuMg2-xLix (x ~ 0.11), with a hexagonal structure, space group P6222 (180), and lattice parameters a = b = 0.5260 nm, c = 1.3649 nm [1]. The structure was refined by the Rietveld method [2]. In order to characterize the thermal behaviour of the ternary compound and to assess the Cu-Li-Mg phase diagram [3], HT-XRD measurements were performed on samples whose compositions were close to the one corresponding to the ternary compound. SEM/EDS measurements of the phases’ compositions in equilibrium, as well as DSC/DTA heating curves, contributed to the identification of the transition temperatures and the phases present in equilibrium. It was concluded that the ternary phase decomposes at ~ 702 ± 2K. Introduction The Cu-Li-Mg system has not been, till now, the object of many studies although it is one of the ternaries of the Al-Cu-Li-Mg system which has been deeply studied, at least near the quasicrystalline T2 (Al6Li3Cu) phase, and which has many applications in the aeronautic industry. Mel’nik et al. [4] referred to the existence of a ternary phase in the Cu-Li-Mg system: Cu8Li2Mg15 with an orthorhombic structure (a = 0.524 nm, b = 0.899 nm, and c = 5.433 nm). Hämäläinen et al. [3] assessed the phase diagram of the system. Figure 1 presents two vertical sections for x(Li) = 0.04 and x(Li) = 0.07 from the Gibbs energy parameters obtained in [3]. In previous work, the present authors pointed out the existence of a phase with a stoichiometry close to that of Cu8Li2Mg15 [5] and, in recent work, the latter phase was defined as being CuMg2-xLix (x ~ 0.11) [1]. Taking into account that there were no experimental data about the thermal behaviour of the ternary phase, nor the high temperature equilibria, 300 European Powder Diffraction Conference, EPDIC 10 and that quenching seemed ineffective for such a narrow temperature range, some HT-XRD studies were developed. On the other hand, an important feature for a successful assessment is the crystallographic data; thus the models used to describe the phases should be supported by the phase’s crystal structure.

Increasing the reactive surface area of a Li three dimensional negative electrode by morphology control

The theoretical grounds establishing the ideal composition, temperature, and time to attain the highest interconnected interface area within a liquid miscibility gap were developed. A three dimension (3D) negative electrode (having low polarization, low density, and interconnected channels) based on the Li-LiH system is proposed for Li conversion batteries. Using the Gibbs free energy of the Li-LiH liquid phase and phase field simulations, we determined the corresponding 3D morphology finding the ideal conditions to increase the electrodes reactive surface area. The optimal morphology was obtained for the composition xH = 0.413 (in the Li-H system).

Neutron Scattering to Characterize Cu/Mg(Li) Destabilized Hydrogen Storage Materials

Cu-Li-Mg-(H,D) was studied as an example of destabilizer of the Ti-(H,D) system. A Cu-Li-Mg alloy was prepared resulting in the formation of a system with 60.5 at% of CuLi 0.08 Mg 1.92 , 23.9 at% of CuMg 2 and 15.6 at% of Cu 2Mg. Titanium was added to a fraction of this mixture so that 68.2 at% (47.3 wt%) of the final mixture was Ti. The mixture was ground and kept at 200 °C/473 K for 7h under H 2 or 9h under D 2 at P = 34 bar. Under those conditions, neutron powder diffraction shows the formation of TiD 2, as well as of the deuteride of CuLi 0.08 Mg 1.92. Similarly inelastic neutron scattering shows that at 10 K TiH 2 is present in the sample, together with the hydride of CuLi 0.08 Mg 1.92 . Interestingly, at 10 K TiH 2 is very clearly detected and at 300 K TiH 2 is still clearly present as indicated by the neutron vibrational spectrum, but CuLi 0.08 Mg 1.92 -H is not detected anymore. These results indicate that Ti(H,D) 2 is possibly formed by diffusion of hydrogen from the Cu-Li-Mg-(H,D) alloys. This is an intriguing result since TiH 2 is normally synthesized from the metal at T > 400°C/673 K (and most commonly at T ~ 700 °C/973 K). In the presence of CuLi 0.08 Mg 1.92 , TiH 2 forms at a temperature that is 300 – 400 K lower than that needed to synthesize it just from the elements.

Nontraditional, Safe, High Voltage Rechargeable Cells of Long Cycle Life

A room-temperature all-solid-state rechargeable battery cell containing a tandem electrolyte consisting of a Li+-glass electrolyte in contact with a lithium anode and a plasticizer in contact with a conventional, low cost oxide host cathode was charged to 5 V versus lithium with a charge/discharge cycle life of over 23,000 cycles at a rate of 153 mA·g-1 of active material. A larger positive electrode cell with 329 cycles had a capacity of 585 mAh·g-1 at a cutoff of 2.5 V and a current of 23 mA·g-1 of the active material; the capacity rose with cycle number over the 329 cycles tested during 13 consecutive months. Another cell had a discharge voltage from 4.5 to 3.7 V over 316 cycles at a rate of 46 mA·g-1 of active material. Both the Li+-glass electrolyte and the plasticizer contain electric dipoles that respond to the internal electric fields generated during charge by a redistribution of mobile cations in the glass and by extraction of Li+ from the active cathode host particles. The electric dipoles remain oriented during discharge to retain an internal electric field after a discharge. The plasticizer accommodates to the volume changes in the active cathode particles during charge/discharge cycling and retains during charge the Li+ extracted from the cathode particles at the plasticizer/cathode-particle interface; return of these Li+ to the active cathode particles during discharge only involves a displacement back across the plasticizer/cathode interface and transport within the cathode particle. A slow motion at room temperature of the electric dipoles in the Li+-glass electrolyte increases with time the electric field across the EDLC of the anode/Li+-glass interface to where Li+ from the glass electrolyte is plated on the anode without being replenished from the cathode, which charges the Li+-glass electrolyte negative and consequently the glass side of the Li+-glass/plasticizer EDLC. Stripping back the Li+ to the Li+-glass during discharge is enhanced by the negative charge in the Li+-glass. Since the Li+-glass is not reduced on contact with metallic lithium, no passivating interface layer contributes to a capacity fade; instead, the discharge capacity increases with cycle number as a result of dipole polarization in the Li+-glass electrolyte leading to a capacity increase of the Li+-glass/plasticizer EDLC. The storage of electric power by both faradaic electrochemical extraction/insertion of Li+ in the cathode and electrostatic stored energy in the EDLCs provides a safe and fast charge and discharge with a long cycle life and a greater capacity than can be provided by the cathode host extraction/insertion reaction. The cell can be charged to a high voltage versus a lithium anode because of the added charge of the EDLCs.

First principles, thermal stability and thermodynamic assessment of the binary Ni–W system

Abstract The Ni–W binary system was assessed using critically evaluated experimental data with assistance from first principles analysis and the CALPHAD method. The solution phases (liquid, fcc-A1 and bcc-A2) were modeled using the substitutional regular solution model. The recently discovered Ni8W metastable phase was evaluated as Fe16C2-like martensite with three sublattices, and shown to be possibly stable according to first principles calculations. Ni8W was also modeled as an interstitial compound, but the model is not good because the solubility of tungsten in nickel is very low, especially at low temperatures. There is no experimental evidence for such low solubility. The other binary compounds Ni4W and Ni3W were assessed as stoichiometric ones. Compared independent experimental and first principles data agree well with the calculated phase diagram using updated thermodynamic parameters.