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This paper describes a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell. The cell is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymer-ceramic materials, and a solid-state composite air cathode prepared from high surface area carbon and ionically conducting GC powder. The cell exhibited excellent thermal stability and rechargeability in the 30-105 C temperature range. It was subjected to 40 charge-discharge cycles at current Densities ranging from 0.05 to 0.25mA/sq cm. The reversible charge/discharge voltage profile of the Li-O2 cell with low polarizations between the discharge and charge are remarkable for a displacement-type electrochemical cell reaction involving the reduction of oxygen to form lithium peroxide. The results represent a major contribution in the quest of an ultra high energy density electrochemical power source. We believe that the Li-O2 cell, when fully developed, could exceed specific energies of 1000 Wh/kg in practical configurations., Prepared in cooperation with Univ. of Dayton, Dayton, OH. and E-KEM Sciences, Needham, MA.

The work carried out under this contract had its primary goal, the development of a polymer electrolyte-based rechargeable battery with the rate capability and cycle life required by batteries for the Army's communication devices. In particular, the battery is to perform over the temperature range of 239 to 343 K. The cell being developed has the configuration: Li/solid polymer electrolyte (SPE)/LiMn2O4. Polyacrylonitrile (PAN) based electrolytes with improved low temperature conductivity can be prepared with the use of carefully selected plasticizer compositions from ternary solvent mixtures consisting of propylene carbonate (PC), ethylene carbonate (EC) and butylene carbonate (BC), or from mixtures of PC, EC and 3-methyl-2-oxazolidinone (MEOX). All of the polymer electrolytes were prepared as free-standing films with a thickness of approx. 4.5 mil. Their conductivities were of the order of 0.003 S/cm at 298 K and 0.00011 S/cm at 233 K. They exhibited good stability to oxidation with oxidative currents of the order of 0.5 microamps per square centimeter at 4.2V versus a metallic lithium reference electrode on aluminum.

The Li/SOCl2 chemical couple represents the highest energy density electrochemical cell presently available, both with respect to volume and weight. The cell has an open circuit potential of 3.65V, a theoretical gravimetric energy density of 670 Wh/lb (1470 Wh/Kg), and a volumetric energy density of 33 Wh/in3 (2.0 Wh/cm3). Energy densities of up to 300 Wh/lb and 21 Wh/in(3) have been realized in practical D size Li/SOCl2 cells. Despite the attractive features such as high energy density, high load voltage and wide operational temperature range, some important problems persist hindering its widespread application. Notable among these is voltage delay, i.e., the initial depression of the cell voltage below 2.0V on load after prolonged storage, especially storage at 70 deg C followed by discharge at high rates and low temperatures. The Li anode instantaneously forms a protective film of LiCl on its surface when it comes in contact with the SOCI2/LiAlCl4 electrolyte. Although the reaction of Li and SOCl2 is strongly favored by thermodynamics, the formation of this LiCl film passivates the Li, kinetically hindering the reaction. Prolonged storage of the cell leads to an increase in the thickness of the LiCl film, and voltage delay is associated with this passivating film.

Several methods have been developed to dimensionally stabilize polymer electrolytes based on poly-(bis(methoxyethoxyethoxide)phosphazene, known as MEEP. In contrast to the poor dimensional stability exhibited by complexes of MEEP with most Li salts, those prepared with LiAICI4 have been isolated as the first example of free-standing MEEP-(LiX)n films. The mechanical properties of dimensionally unstable MEEP-(LIX)n complexes can be significantly improved by forming composites with polymers such as poly(ethylene oxide), poly(propylene oxide), poly(ethylene glycol diacrylate) and poly(vinyl pyrrolidinone). The conductivity of 0.000067 per ohm per cm at 25C exhibited by 55 w/o MEEP/45 w/o PEO-LiN(CF(3)SO(2)20.13 is among the highest values reported to date for a dimensionally stable electrolyte. The preparation, and conductivity, calorimetric and electrochemical studies of these electrolytes are described. Cyclic voltammetric data indicated that these electrolytes have anodic stability at least up to 4.5V versus Li+/Li. They have shown excellent compatibility with Li metal making them suitable for use as Li+ conductive solid electrolytes in solid-state Li batteries. Li/TiS2 solid-state cells utilizing some of these electrolytes have exceeded 200 cycles. (R.H.)

Studies of lithium/Titanium Sulfide cells utilizing polybis(methoxyethoxyethoxide) phosphazene) (MEEP) based polymer electrolytes have demonstrated the excellent potential of this inorganic polymer electrolyte for use in solid-state rechargeable Li batteries of applications at or near room temperature. A major drawback of the MEEP electrolyte has been its lack of dimensional stability, manifested in its tendency to flow. This flow property prevented the preparation of thin film solid electrolytes. A solution to this problem has been found in this program by blending MEEP with poly(ethylene oxide), PEO, which resulted in novel mixed polymer electrolytes exhibiting superior mechanical stability and high conductivity. We have also developed a technique to fabricate solid-state cells with the pure MEEP electrolyte by supporting it on a thin, porous matrix comprising a fiberglass separator.

The European Science Notes Information Bulletin (ESNIB) 89-10 is a compilation of reports on recent developments in European science of specific interest to the U.S. research and development community, and is issued in support of the mission of the Office of Naval Research European Office. Issue Number 89-10, in addition to European area news, notes, and abstracts, contains reports in the fields of Acoustics, Materials, Mathematics, Mechanics, Psychology, Physics, and the Subject Index of 1989 ONREUR Publications. It is not intended to be part of the scientific literature. The value of the ESNIB to Americans is to call attention to current activity in European science and technology and to identify the institutions and people responsible for these efforts. The ESNIB authors are primarily ONREUR staff members; other reports are prepared by or in cooperation with staff members of the USAF European Office of Aerospace Research and Development or the U.S. Army Research, Development and Standardization Group. Scientists from the U.S. who are traveling in Europe may also be invited to submit reports. Keywords: Foreign technology, Scientific literature.

As part of the ongoing High Energy Batteries for Weapons Programs at NSWC, various cell parameters were investigated to examine their effect on the performance, safety, and chemistry of Li/SOC12 cells. This report summarizes the influence of cobalt dibenzo-tetraazaannulene (Co-TAA) cataylsis on the discharge and overdischarge chemistry and performance of spirally wound commercial C-size cells. Co-TAA catalyst improved the performance and safety of C-size Li/SOC12 cells. The catalyst was most effective at high rate or low temperature operation. The presence of water increased the risk of hazards at high rates of discharge. The generation of gases such as COS, CS2, HC1, etc. was dependent on the internal temperature. Originator supplied keywords include: Lithium Battery, Catalyst, Tetraazaannulene, Thionyl Chloride., See also AD-A157 203.

One of the goals of the Navy's High Energy Batteries for Weapons Block Program is to achieve a better understanding of safety hazards in high energy lithium batteries. To attain this objective, a statistical survey was planned to examine how various cell parameters (cell design, cell balance, catalysis, moisture content, etc.) would affect performance and safety in Li/SOC12 cells. Five replicate tests were planned for each cell parameter during various modes of testing including overdischarge, partial discharge and storage followed by further discharge, etc. Cell performance, and individual electrode potentials, cell internal and external temperatures, and pressure were measured during discharge and forced over-discharge at different rates at ambient and subambient temperatures. The effect of partial discharge and storage on cell performance was assessed. At various stages, the cell chemistry was compared using X-ray, gas chromatography, IR and mass spectrocopy techniques. The effects of water, the presence of a catalyst and lithium vs. cathode-limited cell balance were also examined. The data have been summarized in two reports. This first report primarily addresses the effect of test conditions and cell parameters on performance and chemistry. The second report will discuss the effect of the catalyst., See also AD-A157 383.

In this study we investigated the formation of protective surface films on in situ freshly Li in LiAlCl4/SOCl2 electrolytes using electro-chemical techniques. Based on the results we propose a film model consisting of three region. Region I forms rapidly (less than one hour) upon exposure of a fresh surface. It has a thickness between 200 and 400 A and an apparent resistivity of -2.10 7 cm. It appears to have significant imperfection and some microporosity along the grain boundaries. This is followed by a Region II film which is more ordered and more compact. Its resistivity is approximately 2.l0 to the 8th power cm and it grows to 200 to 600 A within a 20 hour period. Further growth is slow. (Author)

The lithium/sulfur dioxide primary electrochemical cell has received considerable attention as a high energy power source in the last decade. However, during the same time a number of safety hazards have been associated with its use. This report is the initial part of a research-oriented investigation intended to identify and document present Li/SO2 safety hazards, then to identify the chemical reactions responsible for these hazards, and finally to investigate methods of controlling them. This report presents the results of a survey of the safety hazards associated with Li/SO2 cells. The report documents specific safety incidents experienced with Li/SO2 cells, presents some of the causes identified or postulated for the incidents, and identifies general aspects of Li/SO2 use presently believed to be potentially hazardous. The survey was carried out by reviewing safety studies and reports of safety incidents appearing in the literature and by gathering unpublished information of the experiences of users of Li/SO2 cells in both government and industry. The results of the report can serve as basis for deciding which aspects of the Li/SO2 safety hazard at present need further investigation.

The cathodic behavior or V6013 was investigated in rechargeable Li cells of the type, Li/2Me-THF,LiAsF6/V6013,C. Two forms of V6013 were synthesized and characterized. These were a stoichiometric form, i.e., V02.17, and a slightly non-stoichiometric form, i.e., V02.19. Stoichiometric V6013 was prepared by heating requisite quantities of V205 and V powder for 24 hrs. at 650 C. The slightly non-stoichiometric V6013 was prepared by the thermal decomposition of NH4V03 at 450 C. The discharge characteristics of the stoichiometric oxide at 60 C were similar to that of non-stoichiometric oxide at room temperature. The rechargeability of both the oxides were found to be sensitive to the lower voltage cutoff. The safest limits of cycling were 3.0 and 1.9V. Potentiostatic discharges of the oxides between 1.9 and 1.3V revealed a high capacity irreversible reduction process at about 1.6V. Three types of hermetically sealed cells were constructed and tested. In a high capacity (5Ah) prismatic cell utilizing the non-stoichiometric oxide, energy densities of 106 Whr/kg and 190 Whr/DM3 were achieved.

The safety related chemistry of the Li/SO2 battery has been further investigated. The normal discharge stoichiometry, 2 Li + 2SO2 yields Li2S2O4, has been confirmed for current densities up to 8 mA/sq. cm at room temperature, and for discharges at -25 C. Experiments have revealed that Li2S2O4 in the carbon cathode decomposes at approx. 180 C producing one mole of SO2 per three moles of Li2S2O4. The other decomposition products are S, Li2SO3, and small amounts of CO2, COS and CS2. The decomposition of forced overdischarged cathodes containing Li2S2O4 and Li appears to occur at an accelerated rate at approx, 180 C, producing larger quantities of COS, CO2 and CS2, along with SO2. The higher exothermicity of the latter composition is believed to be due to the reduction of Li2S2O4 by Li. A preliminary study of the chemistry in partially discharge and stored cells has been carried out. Li-polythionates along with Li2S2O4 have been identified on the anodes of such cells. The implication of this chemistry to the safety of the system is not yet understood, The effects of parameters such as current density, depth of discharge, electrolyte composition, and storage time and temperature on the storage chemistry of the battery remain to be assessed.

New catalysts which improve the discharge performance of Li/SOCl2 cells have been identified. These catalysts were obtained by thermal treatment of acetylene black carbon doped with the precursors, Co(NO3)2, manganese phthalocyanine (MnPc) or vanadium phthalocyanine oxide (VOPc). The latter two materials appear to be superior to many catalysts presently available for use in Li/SOCl2 cells. Compared with uncatalyzed cells, MnPc-containing cells showed a 60% increase in cell capacity and a 10% increase in cell voltage at room temperature. VOPc-containing cathodes increased the cell capacity by 50% and cell voltage by 10% under the same conditions. The use of VOPc also resulted in significant improvements in cell performance at low temperature, e.g., at -30 C. Keywords: Catalysis, Lithium batteries, Thionyl chloride.

Cycle lifes of secondary Li cells utilizing THF/LiAsF6 solutions have been significantly improved by the use of small amounts of additives such as 2,methyl-furan, 2,methyl-thiophene or similar unsaturated organic compounds. A most important consequence of the discovery has turned out to be the practical utility of the mixed electrolyte, 50 v/o THF:50 v/o 2Me-THF/LiAsF6(1.5M). This solution combined with approx. 3.5 v/o 2Me-furan has enabled 5 A-hr Li/TiS2 cells to exhibit more than 200 cycles at 60% depth-of-discharge. This cycle life is twice that achieved with 2Me-THF/LiAsF6(1.5M). In addition, the mixed electrolyte cells have shown low temperature discharge capabilities superior to those containing either THF/LiAsF6(1.5M) or 2Me-THF/LiAsF6(1.5M).

Cr0.5V0.5S2 has been characterized as a useful positive electrode material for rechargeable Li cells. The positive electrode reaction involves intercalation of Li during discharge and deintercalation of Li during recharge. A discharge capacity equivalent to nearly le-/Cr0.5Vo.5S2 has been obtained in early cycles at low rates. The average capacity which could be realized in long-term cycling appears to be 0.7-0.8e-/Cr0.5V0.5S2. Laboratory cells exceeded 200 deep discharge cycles. Although Cr0.5V0.5S2 and its Li intercalates are good electronic conductors, optimum rate and rechargeability were found in electrodes with 15-20 weight percent carbon. Because of this relatively large amount of carbon, the volumetric energy density achieved in cells has been significantly lower than what was anticipated at the outset of the program. The major objective of the program, development of a technology base for the construction of large rechargeable Li cells, has been accomplished. Cells with theoretical capacities of 10 and 20 Ah have been constructed and tested. In limited cycle tests, these large cells performed as well as laboratory test cells.

The chemistry associated with the discharge and forced overdischarge of the Li/SO2 cell was investigated in detail. A procedure for the quantitative determination of Li2S2O4 in discharged Li/SO2 cells is described. The amount of Li2S2O4 found in cells discharged to potentials down to zero volt was in very good agreement with the discharge stoichiometry, 2Li + 2SO2 yields Li2S2O4. The Li2S2O4 formed in the carbon cathode was also characterized by infrared, ESCA, and X-ray analyses. A number of organic compounds including CH4 and 3,5-diamino-2,4-hexenenitrile have been identified in forced overdischarged cells. Products identified in cells which vented during forced overdischarge include: CO2, CS2, COS, H2S, CH4, C2H4, C2H2, Li2S, and Li2SO3.

2Methyl-tetrahydrofuran (2Me-THF)/LiAsF6 and several diethyl ether (DEE)/LiAsF6-based electrolytes have been characterized for their usefulness in rechargeable Li/TiS2 cells. This characterization has involved extended room temperature cell cycling at various depths of discharge, evaluation of rate/capacity behavior of cells at 25C and -10C, and storage of cells at 50C for up to one month with subsequent cycling. The thermal stability of the electrolytes at 71C was evaluated by storage experiments in sealed-tubes, followed by product analysis. The performance of 2Me-THF/LiAsF6 cells far surpassed the others. The present data further substantiate previous reports from this laboratory of the superior behavior of 2Me-THF/LiAsF6 solutions in rechargeable Li cells. The DEE/LiAsF6 based electrolytes are too unstable thermally to be practically useful. (Author)

The usefulness of tetrahydrofuran (THF) as a cosolvent with 2-methyltetrahydrofuran (2Me-THF)/LiAsF6 for improving the low temperature rate capability of rechargeable Li cells has been explored. Li/TiS2 cells utilizing 2Me-THF/LiAsF6 blended with 15-50 volume-percent THF have shown substantially improved rate characteristics at 0 and -10C. In addition, the Li electrode in such cells has exhibited practically useful cycling efficiencies. (Author)