Prototype cells of the configuration Li/,~SM S as Li2S,, THF, 1M LiAsF6/C have been characterized with regard to capacity, rate, and rechargeability. Virtually 100% of the theoretical capacity could be realized at 50~ at rates below 1.0 mA/cm 2. In high rate cell configurations, 75% cathode utilization is possible at ,-.4 mA/cm 2 (C/3-C/4rate). The capacities at high rate are enhanced by Lewis acids, although the ultimate cause of rate limitation is passivation of the current collector by discharge products. The self-discharge rates of Li in contact with 4-5M S (as Li2Sn) solutions reveal capacity losses of 0.5%/day at 25~ to 4.4%/day at 71~ Based on the experimental results, a practical energy density of ~300 W-hr kg-' is possible using a standard cell design. Results on the battery's rechargeability are briefly reviewed.An ambient temperature Li/S battery utilizing an organic electrolyte has many attractive possibilities, among them high energy density, and the use of relatively low cost, relatively safe materials. Previous attempts to develop such a cell have involved the incorporation of insoluble Ss directly into the current collector (1-3). In general, very poor discharge efficiencies were obtained. One explanation put forth for these results is that some of the Ss was reduced to soluble polysulfide, Sn -2, which "escaped" from the cathode current collector and self-discharged on the Li anode (4). One recent moderately successful approach to increasing the S utilization efficiency was to add a Lewis acid, BF3, supposedly to suppress polysulfide formation (4, 5).The highest rate Li batteries, such as Li/SOC12 (6-8) and Li/SO2 (9, 10), have employed liquid cathodes. Here, very good electrical contact is maintained between the cathode material and the current collector through all phases of discharge. Both Ss and its ultimate discharge product, Li2S, are electrical insulators. Thus, it is likely that insulation of the cathode material, rather than S,~ -~ formation, led to poor results for Li/S cells. In our experience, the reaction between Li and dissolved Sn -2 is very slow, and the formation of dissolved Sn -2 enhances cathode utilization. In this regard, the explanation of the effect of BF8 on sulfur utilization is not very convincing.In contrast to most previous work on Li/S batteries, we have chosen to investigate a system where the S is completely dissolved in the electrolyte, as Li2S~ (11,12). Hence, the theoretical cell reaction becomes

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Condensation of s i l i c a from b r i n e s supersaturated i n s i l i c i c a c i d w a s s t u d i e d over a range of pH (4.5-6. S), temperature (75O-l05OC), s a l i n i t y , and s i l i c i c a c i d concentration (700 t o 1200 ppm as Si02). technique involved analyses f o r molybdate-reactive s i l i c i c a c i d as a function of t i m e a f t e r a supersaturated s o l u t i o n of Si(OH)4 was prepared by mixing a l i q u o t s of a s t o c k s i l i c a t e s o l u t i o n with buffered b r i n e .

This report describes work carried out on the development of rechargeable, ambient temperature Li/sulfur and Li/metal sulfide batteries. The Li/S system has the cathode material dissolved in the electrolyte, as Li2S n. Tetrahydrofuran, 1M LiAsF6, is one of the more attractive electrolytes discovered for this cell, since it can dissolve up to ^10M S as Li2S n. Despite the oxidative nature of the electrolyte, Li is stable in it and can be electrodeposited from it on battery charge. Passivation of the Li due to insoluble Li +-permeable films is thought to be responsible for this stability. Cells of the configuration Li 5M S(as Li2S n), THF, 1M LiAsFs/carbon can be discharged at 50°C with a utilization of nearly 1.5e"/S at the C/3 rate. This corresponds to our rate-capacity goal for this battery (>50% utilization at C/3) in its proposed vehicular or load-leveling applications. Further improvements in rate are possible with Lewis acidic • catalysts such as 3B or Ba + 2. Rechargeability of 135 cycles of 0.1e"/S and ^45 cycles of 0.5e~/S have been demonstrated for this cell. The self-discharge reaction keeps the Li electrode free of electrically isolated dendrites. Ultimate failure on cycling is due to cathode depletion via precipitation of Li2S on the anode in a form which is insoluble in the electrolyte. To date, attempts to solubilize the Li2S by the internal generation of an oxidizing "scavenger" (e.g., Br2) or by addition of Lewis acids have met only with limited success. Cells of configuration Li/THF, 1M LiAsF6/insoluble metal sulfide were investigated, using the following cathodes: CuS, NiS, SiS2, MnS2, FeS and Bi2S3. Of these, the most promising new material in terms of energy density and rechargeability is CuS. Well over 100 cycles for Li/CuS cells with moderate cathode loadings have been demonstrated, giving cathode efficiencies of >0.8 eq/mole. CuS compares favorably with TiS2 in terms of energy density and rechargeability and is superior in terms of economics.

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