Anthony F. Sammells

Thermodynamic Studies of Li‐Ge Alloys: Application to Negative Electrodes for Molten Salt Batteries

The objectives of this work are (i) to gain some preliminary understanding of the electrochemical and chemical characteristics of Li-Ge alloys under the conditions present in the lithium-metal sulfide battery system in order to identify the feasibility of using germanium as an additive to lithium alloys currently being investigated for this battery system and (ii) to evaluate the Li-Ge alloy system for its inherent utility as a negative electrode for molten salt batteries. 33 refs.

Galvanic Cells Containing Cathodes of Iron‐Doped Beta‐Alumina

Galvanic cells of the form Na//~-alumina/Na20.11(Fe~A12-=O~) where x varied between 0.9 and 1.2 were operated at 120~ and currents of 50 m A / c m 2 could be drawn. The cells were electrochemically regenerative, and the cathodes could be thermal ly regenerated. Ini t ia l open-circuit voltages varied between 2.37 and 2.45V. Cells were discharged at constant current, and two distinct voltage regions were observed. The reduction process was investigated by MSssbauer spectroscopy. The lower voltage region was shown to involve the reduction of Fe 3+ to Fe 2+. The higher voltage region is possibly explained by the filling of holes in the valence band of the i ron-doped spineltype structure, created dur ing the sintering process. Sodium E-alumina Na20.11 A1203 has become increasingly attractive as an electrolyte in recent years due to its relat ively high conductivity and its applicabi l i ty to alkali metals (sodium in part icular) as potential anode materials. Be ta -a lumina single crystals have been shown to exhibit rapid sodium ion diffusion in the plane perpendicular to the c-axis (1), and the sodium ions can be almost completely exchanged in molten salts for Ag, K, Li, Rb, and to a lesser extent Cs ions. This ion exchange property infers ion conduct ivi ty and makes B-alumina an electrolyte also worthy of consideration in any bat tery systems that incorporate K or Li as anode materials. Sodium ions, however, exhibit the largest diffusion coefficient, the mechanism of which has been shown to be interstitial. Interest in E-alumina as a sodium ion conducting electrolyte has revolved around its use in the sodium/sul fur bat tery first reported by K u m m e r and Weber (2). This bat tery operates in excess of 300~ due to the high mel t ing point of the sodium polysulfide cathode mater ia l used. Many of the early investigations with B-alumina as a sintered polycrystal l ine mater ia l were concerned not only with the achievement of high conductivity but also with the deterioration of the electrolyte at such temperatures. The development of batteries operative st temperatures considerably below 300~ has been l imited by low conductivities of the sintered electrolyte mater ia l and the avai labi l i ty of suitable cathode materials. Recent investigations (3-5) have shown that sodium ion conductivi ty in sintered B-alumina can be sufficiently increased by the incorporation of MgO to make E-a lumina feasible as an electrolyte at temperatures considerably below 300~ Cathode materials for E-alumina galvanic cells present more formidable problems. The subst i tut ion of M 3+ transi t ion metals for A13+ sites in E-alumina was first suggested for cathode mater ia l by Hever (6) who synthesized cathode materials of the stoichiometry (a) Na20-5 (Fe0.95Ti0.0~A103), and (b) 1.3 K20-0.2Na20.10 * E l e c t r o c h e m i c a l Soc ie ty A c t i v e Member . * Electrochemical Society S t u d e n t Associa te . K e y words: battery cell, beta-alumina, iron sp ine ls , MSssbaue r spectroscopy, sodium elect rode. (Fel.gTi0.103). Cell (a) used the electrolyte M-br ick (Harb ison-Carborundum) which consists of an a -a lumina /B-a lumina eutectic in which the presumed mobile species was Na § The electrolyte used in cell (b) was 1.3 K20-0.2 Li20-10 AI~O~ in which K + was assumed to be the mobile species. In these cells both of the electrodes consisted of the same material, and the cell was charged after fabrication. The t ransi t ion metal ions were considered to be immobile, and the electrochemical process taking place in the cathode did not involve a phase change. It was postulated that the measured voltage came from the reduct ion of M 3+ to M 2+ accompanied by the migrat ion of Na + through the electrolyte to main ta in electroneutrali ty. T i tan ium dioxide was added to the cathode mater ial to increase the electronic conductivi ty by providing F d § donor ions. These cells ran at 300~176 under vacuum (10 -4 Torr) and exhibited potentials of < 1V. The cells had identical electrodes in which one acted as an anode while the other acted as a cathode. The charge capacity was l imited by the avai labi l i ty of Na + in the electrolyte material. In order to devise a cell using sodium B-alumina electrolyte which is not l imited by the amount of electrolyte material, the anode must supply the needed sodium ions. The na tura l choice for such an anode is sodium metal. We report here electrochemical cells which were operated at temperatures just above the mel t ing point of sodium and contained sintered cathodes in which some of the A1 ~+ sites were replaced by Fe d+ in the B-alumina structure.

A Zinc Chlorine Molten Salt Cell

The feasibility of using molten salt electrolytes in the zinc/chlorine system is examined. It would seem unlikely that very high current densities are practical with the molten salts studies (ZnCl/sub 2/--NaCl--KCl, ZnCl/sub 2/--NaCl and ZnCl/sub 2/--KCl eutectics). Greater discharge rates may result from increased electrolyte conductivities and optimization of the chlorine electrode performance.