Lithium-ferrate-based cathodes for molten carbonate fuel cells

Argonne National Laboratory is developing advanced cathodes for pressurized operation of the molten carbonate fuel cell (MCFC) at approximately 650 degrees Centigrade. These cathodes are based on lithium ferrate (LiFeO[sub 2]) which is attractive because of its very low solubility in the molten (Li,K)[sub 2]CO[sub 3] electrolyte. Because of its high resistivity, LiFeO[sub 2] cannot be used as a direct substitute for NiO. Cation substitution is, therefore, necessary to decrease resistivity. The effect of cation substitution on the resistivity and deformation of LiFeO[sub 2] was determined. The substitutes were chosen because their respective oxides as well as LiFeO[sub 2] crystallize with the rock-salt structure

Strain effect on electronic transport and ferromagnetic transition temperature in La0.9_{0.9}Sr0.1_{0.1}MnO3_{3} thin films

We report on a systematic study of strain effects on the transport properties and the ferromagnetic transition temperature $T_{c}$ of high-quality La$_{0.9}$Sr$_{0.1}$MnO$_{3}$ thin films epitaxially grown on (100) SrTiO$_{3}$ substrates. Both the magnetization and the resistivity are critically dependent on the film thickness. $T_{c}$ is enhanced with decreasing the film thickness due to the compressive stain produced by lattice mismatch. The resistivity above 165 K of the films with various thicknesses is consistent with small polaronic hopping conductivity. The polaronic formation energy $E_{P}$ is reduced with the decrease of film thickness. We found that the strain dependence of $T_{c}$ mainly results from the strain-induced electron-phonon coupling. The strain effect on $E_{P}$ is in good agreement with the theoretical predictions.Comment: 6 pages and 5 figures, accepted for publication in Phys. Rev.

Li1.5La1.5MO6 (M = W6+, Te6+) as a new series of lithium-rich double perovskites for all-solid-state lithium-ion batteries

Solid-state batteries are a proposed route to safely achieving high energy densities, yet this architecture faces challenges arising from interfacial issues between the electrode and solid electrolyte. Here we develop a novel family of double perovskites, Li1.5La1.5MO6 (M = W6+, Te6+), where an uncommon lithium-ion distribution enables macroscopic ion diffusion and tailored design of the composition allows us to switch functionality to either a negative electrode or a solid electrolyte. Introduction of tungsten allows reversible lithium-ion intercalation below 1 V, enabling application as an anode (initial specific capacity >200 mAh g-1 with remarkably low volume change of ∼0.2%). By contrast, substitution of tungsten with tellurium induces redox stability, directing the functionality of the perovskite towards a solid-state electrolyte with electrochemical stability up to 5 V and a low activation energy barrier (<0.2 eV) for microscopic lithium-ion diffusion. Characterisation across multiple length- and time-scales allows interrogation of the structure-property relationships in these materials and preliminary examination of a solid-state cell employing both compositions suggests lattice-matching avenues show promise for all-solid-state batteries

Superplastic behavior of a fine-grained Mg-9Li material

A fine-grained (/ = 1.5 /xm) laminate containing 91.0 wt. % magnesium and 9.0 wt. % lithium was prepared by a foil metallurgy technique involving rolling and pressing at low homologous temperature (0.39-0.49 Tm). The processed material exhibits superplastic characteristics above 70 CC (0.40 Tm). The strain-rate-sensitivity exponent is about 0.5 and an elongation-to-failure of 450% was obtained at 100 °C (0.43 Tm). The activation energy for plastic flow in the superplastic region is 65 kJ/mole. This value of the activation energy is related to the expected activation energy for grain boundary diffusionThe United States Office of Naval Research provided financial support for this program under Contract No. N-00014-91-J-1197.Peer reviewe

Creep behavior of single-phase γ-TiAl

Creep data of single-phase γ-TiAl alloys from different sources can be explained by a single deformation mechanism that incorporates a threshold stress. It is suggested that the creep behavior of single-phase γ-TiAl alloys is controlled by a dislocation climb process (n≈ 4.5) with an activation energy for creep of about 313 kJ/mol. © 1994.Peer Reviewe

Processing and superplastic properties of fine-grained iron carbide

Fine-grained iron carbide material (80 vol pct iron carbide and 20 vol pct of an iron-base second phase) was prepared using two different powder metallurgy procedures: (1) hot isostatic pressing followed by uniaxial pressing and (2) hot extrusion followed by uniaxial pressing. Both procedures yield materials that are superplastic at elevated temperature with low values of the stress exponent (n = 2 to 1) and tensile elongations as high as 600 pct. The strain rate in then = 2 region is inversely proportional to approximately the cube of the grain size with an activation energy for superplastic flow between 200 and 240 kJ/mol. It is postulated that superplastic flow in the iron carbide material, in then = 2 region, is grain-boundary sliding accommodated by slip controlled by iron diffusion along iron carbide grain boundaries. The flow stress in compression is about 2 times higher than in tension in the region where grain-boundary sliding is the rate-controlling process. It is believed that the difference in flow stress is a result of the greater ease of grain-boundary sliding in tension than in compression. Tensile elongations were observed to increase with a decrease in stress and a decrease in grain size. These effects are quantitatively explained by a fracture mechanics model that has been developed to predict the tensile ductility of superplastic ceramics.Peer reviewe

Tension versus compression superplastic behavior of a Mg-9 wt% Li-5 wt% B4C composite

A fine-grained (2 μm) Mg-9 wt% Li-5 wt% B4C particulate composite was superplastic in the temperature range 150-200°C. The flow stress in compression was about two to three times higher than in tension in the superplastic region. This difference is attributed to a greater ease of grain-boundary sliding in tension than in compression. © 1992.Peer Reviewe

Mixed Electronic and Ionic Conduction Properties of Lithium Lanthanum Titanate

With the continued increase in Li‐metal anode rate capability, there is an equally important need to develop high‐rate cathode architectures for solid‐state batteries. A proposed method of improving charge transport in the cathode is introducing a mixed electronic and ionic conductor (MEIC) which can eliminate the need for conductive additives that occlude electrolyte–electrode interfaces and lower the net additive required in the cathode. This study takes advantage of a reduced perovskite electrolyte, Li0.33La0.57TiO3 (LLTO), to act as a model MEIC. It is found that the ionic conductivity of reduced LLTO is comparable to oxidized LLTO (σbulk = 10−3–10−4 S cm−1, σGB = 10−5–10−6 S cm−1) and the electronic conductivity is 1 mS cm−1. The ionic transference numbers are 0.9995 and 0.0095 in the oxidized and reduced state, respectively. Furthermore, two methods for controlling the transference numbers are evaluated. It is found that the electronic conductivity cannot easily be controlled by changing O2 overpressures, but increasing the ionic conductivity can be achieved by increasing grain size. This work identifies a possible class of MEIC materials that may improve rate capabilities of cathodes in solid‐state architectures and motivate a deeper understanding of MEICs in the context of solid‐state batteries.Lithium lanthanum titanate can exhibit both high ionic conductivity and high electronic conductivity depending on its oxidation state. While electronic conductivity in solid electrolytes is typically undesirable, the ability to conduct both Li‐ions and electrons may pose useful for cathode composites. This work investigates the conduction properties of lithium lanthanum titanate and potential methods to control transference number.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154428/1/adfm201909140_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154428/2/adfm201909140-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154428/3/adfm201909140.pd