The electrochemical behavior of the magnesium electrode in thionyl chloride (TC) solutions was studied. It was found that this electrode is covered by a passivating layer which consists of some insoluble magnesium salt, probably MgCl2 . The properties of this layer determine the chemical and electrochemical behavior of the electrode in TC solutions. Magnesium was deposited on a nickel cathode from TC solutions containing normalMgfalse(FeCl4)2 . Magnesium deposition begins after the nickel cathode is covered by a passivating layer (consisting of reduction products of TC) in which tMg2+∼1 . It was concluded that the rds for the deposition‐dissolution process of the magnesium electrode in TC solutions is not the electron‐transfer reaction, but is instead the migration of the Mg2+ ions through a passivating layer which covers the electrode.

The lithium-SO2 cell shows good performance over a wide range of temperatures and a good shelf life. In addition, it has the highest power density of all commercially available cells (1). For example, a C-size cell is capable of continuously delivering 1.5A at room temperature (2). However, because of hazard limitations, its recommended maximum continuous rate is only 0.36A (2). Recently, both the safety and rate capability of the Li-SO2 system were improved (3-5), and the recommended maximum continuous rate was doubled. All of this was accomplished by, among other things, the use of balanced Lito-SO2 ratio and greater electrode area. The main hazard factors in high rate lithium cells are the deposition of very reactive high surface area lithium during reversal and charging abuses (6-8).The calcium-thionyl chloride system has recently attracted attention, as a safer alternative to lithium high rate cells (9-17). Encouraging electrical performance was obtained for cells of various sizes -between 3.5 and 2000 Ah -containing LiAIC14 electrolyte (15)(16)(17).Recent studies in our laboratory, with the use of small laboratory cells (10 cm 2 electrode area) containing Ca(AICI~)2 electrolyte, have shown (9-12) good electrical performance and much better safety characteristics. Unlike lithium cells or the Ca/LiA1C14-TC cell, the Ca/Ca(A1C14)2-TC cell successfully resists charging and reversal abuses (9-12). It behaves like an "electrochemical diode" (11, 12), Le., it delivers high current densities (up to ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 137.99.31.134 Downloaded on 2015-06-01 to IP Vol. 131,No. 10 Ca/Ca(A1C14)2--THIONYL CHLORIDE CELL

The lithium-thionyl chloride cell has the highest energy density among all the commercially available batteries. The low rate, AA-bobbin cathode cell has been in the marketplace for several years while the wound or spiral electrode cell is still in the stage of development and not commercially available. The main reason for this is that the safety hazard problems of the high rate version have not yet been completely and satisfactorily understood and solved. The basic reasons for the safety hazard problems are the very high reactivity of lithium toward thionyl chloride and the rather low melting point of lithium (180.5~The practical stability of this system and the excellent storageability of this cell is due to an LiCl-passivating layer which forms spontaneously on the immersion of the lithium in the electrolyte. The part of this layer that is close to the lithium surface serves as a solid electrolyte interphase (SEI) through which only lithium can pass (1-5).As the electronic conductivity of the SEI is very low it retards further corrosion of the anode. This SEI covers the lithium not only on OCV but also during plating and stripping (charging and discharging). As long as the lithium anode is fully covered by the LiC1-SEI, no hazardous conditions are created. This SEI can be momentarily damaged in several ways, such as plating, anodic stripping, or by mechanical deformation of the lithium. In most cases it will heal immediately by fast precipitation of LiC1 (a corrosion product of lithium with thionyl chloride). However, in extreme conditions, such as hot spots, electric sparks, and a fast melting of lithium, the SEI cannot be fully healed due to either a fast streaming of molten lithium, or a fast local evaporation of lithium. As a result a very exothermic reaction of molten lithium with thionyl chloride occurs possibly resulting in an explosion of the cell.Cells in which the electrode surface area is high have a very high short-circuit current. As a result an internal or external short leads to a fast heating of the * Electrochemical Society Active Member. ~Present address: Tel-Aviv University, Tel-Aviv, Israel. Work performed at GTE Laboratories while on sabbatical. 2 Present address: Duracell, Incorporated, Burlington, Massachusetts.cell, fast melting of lithium anode (above 180~ and finally to explosion. A possible way to improve the safety performance of lithium cells, still under experimental development and testing, is to use lithium alloys instead of pure lithium. The compatibility of several lithium alloys with thionyl chloride was recently studied (5). No substantial difference was found between pure lithium and the four following alloys~ (Li-6% A1, Li-5% Mg, Li-5% Ca, Li-4% Si) regarding the growth rate of the SEI, the resistivity of the SEI, and the overall corrosion rate. The discharge characteristics and storageability of several lithium alloys in thionyl chloride are described in a recently published technical report (6).The purpose of this work was to study ways to reduce the short-circuit curre...

Durch Zusammenrollen von Ca‐Folie mit Glasseparatoren und teflongebundener C‐Kathode wurde eine Testzelle (C‐size) mit 100 cm2 Elektrodenfläche erhalten, deren volumetrische Energiedichte mit der von Li‐SO2‐Zellen vergleichbar ist.

Das chemische und elektrochemische Verhalten der Mg‐Elektrode in Thionylchlorid wird durch eine Passivierungsschicht aus einem unlöslichen Mg‐Salz, wahrscheinlich MgCl2 , bestimmt.