No abstract

A low cost negative electrode for lithium-metal-sulfide batteries has been developed. The electrode, which can be used for cells assembled in the discharged state, is an aluminum disk with a high porosity of 50-60%. It can be prepared by hot-pressing aluminum powder together with NaCI and subsequent leaching with water. The performance of this type of electrode was tested in half-cell arrangements and in complete cells. No polarization was caused by this electrode and it showed almost no swelling after cell operation. This behavior looks promising with regard to a low-cost electrode and cell fabrication. * Electrochemical Society Active Member.Published costs oJ this article were assisted by Bat-teIle-Institut e.V. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.210.126.199 Downloaded on 2015-06-27 to IP

The LiA1/FeS battery with molten KC1-LiC1 electrolyte operates at a temperature of about 450~ and is a promising candidate for load-leveling and traction applications (1-4).As part of the general R&D program of VARTA Batterie AG, Kelkheim, Battelle-Institut e.V., Frankfurt am Main was commissioned to conduct investigations into the self-discharge behavior of LiA1/FeS cells. Although it is well known from the measurement of coulomb efficiencies that the self-discharge rate is relatively low, quantitative data on this important property are not available. The objectives of the work described were therefore (i) to determine quantitatively the rate of self-discharge, (it) to discover the reasons for self-discharge, and (iii) to examine the effect of cell leakages on the rate of self-discharge. In order to isolate the principal effects, the investigations were carried out in cell types in which self-discharge reactions caused by contacts between the electrodes could be excluded from the start. Thus, it was possible to determine the smallest possible self-discharge rate of this battery system. Since this work is in a preliminary stage, an explanation of possible mechanisms of self-discharge is not given. Work in this direction is now in progress. ExperimentThe cells had a utilized capacity of 6 A-hr, limited by the positive electrode. They were assembled in an argon atmosphere in a glove box and operated in open air. Figure 1 shows the cell configuration. The electrodes were about 6 mm thick. The positive electrode was in contact with the stainIess steel casing. It was prepared in the uncharged state by hot-pressing a mixture of Li2S, Fe, and electrolyte powders. In order to prevent mass losses, the electrode was wrapped in a 300-mesh stainless steel screen. The preparation of the negative electrode is described in detail elsewhere (5). This electrode consists of a porous aluminum disk, also wrapped in a stainless steel screen. The distance between the electrodes was about 10-15 mm (investigations involving smaller spacings are now in progress). The capacity of the negative electrode was made about 30% higher than that of the positive electrode. Thus, the ~-field of the Li-A1 phase diagram has not been reached. The observed increase in voltage (see Fig. 2) therefore may be due to the formation of small amounts of FeS2.After having been assembled in the glove box the cells were soldered with a special solder. Conventional current feed throughs with ceramic bodies or spark plugs were used, which were carefully sealed with a ceramic cement. As the feed throughs were not in contact with the melt (see Fig. 1), it was possible to use 99.9% A1203 for the insulating ceramic. No 9 Electrochemical Society Active Member. Key words: lithium metal sulfide battery, self-discharge, molten salt electrolyte. 1311 attack was observed at these materials after the experiments. After heating to the operating temperature of 430~ the cells were charged to 1.6V with constant current (in most cases at a 20 hr rate).The actual rate of self-disc...