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Cubic garnet Li6.24La3Zr2Al0.24O11.98 (LLZO) is a candidate material for use as an electrolyte in Li-Air and Li-S batteries. The use of LLZO in practical devices will require LLZO to have good mechanical integrity in terms of scratch resistance (hardness) and an adequate stiffness (elastic modulus). In this paper, the powders were fabricated by powder processing of cast ingots. All specimens were then densified via hot pressing. The room temperature elastic moduli (Young's modulus, shear modulus, bulk modulus, and Poisson's ratio) and hardness were measured by resonant ultrasound spectroscopy, and Vickers indentation, respectively. For volume fraction porosity, P, the Young's modulus was 149.8 0.4 GPa (P = 0.03) and 132.6 0.2 GPa (P = 0.06). The mean Vickers hardness was 6.3 0.3 GPa for P = 0.03 and 5.2 0.4 for P = 0.06., Pub. in Journal of Materials Science, v47 n23, p7978-7985, 2012.

The Li-CFx chemistry has been traditionally used for low rate applications at discharge rates of C/1000 or lower. The Army is supporting efforts to engineer Li/CFx batteries for Soldier applications that operate at higher rates, closer to C/10. This effort is based on the favorable specific energy and storage characteristics offered by this chemistry. Heat generation under high rate discharge is one potential concern in these batteries and, therefore, further study of the mechanism of heat generation and the differences in heat generation between various CFx materials is warranted. We demonstrate that the thermal power generated when a Li-CFx cell is discharged appears nearly instantaneously in the cell and ceases nearly as quickly when discharge is interrupted. Extrapolation of the running potential to zero heat results in a predicted voltage for the Li/CFx cell of 4.25 V, very near the theoretical potential calculated by Wood, et al. (1). The microcalorimetry results support the two phase model for discharge where a large overpotential, presumably due to the highly disfavored process of breaking covalent C-F bonds, dominates the OCV and running potential of the cell.

The performance of six different commercially available carbon monofluoride (CFx) materials were evaluated at four different discharge rates. The physical and chemical properties of the CFx materials were correlated to cell performance in lithium coin cells. This study was undertaken to determine if there are specific physical or chemical properties that can be tied to performance and if modification of these properties could lead to an improved carbon monofluoride material., The original document contains color images.

A survey is presented of the available literature on the problem of gas evolution in the Li/MnO2 primary battery system during storage. This gassing is due to the breakdown of the solvents, primarily propylene carbonate (PC) and dimethoxyethane (DME). Of these, the major contributor to gassing during storage is PC, which undergoes a hydrolysis reaction to form CO2. This reaction is a function of the amount of absorbed and structural water. Techniques to help eliminate gassing during storage include predischarging and the use of water scavengers, cathode additives, reactive dehydration, properly heat-treated MnO2, weak oxidizing salts, and oxidation-resistant solvents. Although not a major factor in gas evolution in stored batteries, DME has been observed to form methane (CH4) during discharging, probably via an oxidation reaction that is ultimately a function of the absorbed water content. The report also briefly reviews the self-discharge characteristics of Li/MnO2. Three factors determine the self-discharge of Li/MnO2: (1) The oxidation state of the manganese ion. For the types of MnO2 used, it is expected that the self-discharge rate would be low. (2) The nature of the electrolyte salt and amount of absorbed water. Self-discharge is higher for LiClO4 and LiCF3SO3 electrolytes than for fluorinated salt electrolytes. The nature of the solvent. Self-discharge is higher for ethers (e.g., DME) than for carbonates (e.g., PC).

This final report summarizes work accomplished on superplastic ceramics with special emphasis on developing processing methods for creating ultra-fine structures in iron carbide, quantifying its microstructure and assessing its superplastic characteristics. The two principal objectives of this program are (1) to develop processing methods for achieving stable ultrafine grained (in the order of one micron) carbide-base materials, and (2) to evaluate and understand the mechanical behavior of ultrafine grained carbides at high temperatures, with special attention to superplastic flow and failure mechanisms.