Alkali Peroxydisulfates for Water‐Activated Reserve Batteries

Abstract

Peroxydisulfates (persulfates) possess very high specific free energy changes for oxidation in aqueous systems. The alkali persulfates are very soluble and yield, in 40% aqueous systems, cell voltages, at the 4 hr rate, that exceed 2V. Persulfates are stable and can be dry-stored for long periods with little loss of oxidizing power. Used in conjunction with Mg alloy (AZ-61) anodes, persulfate cells can be activated with most common aqueous media. The Na2S2Os/AZ-61 cell has fast start-up capability and a flat discharge characteristic at all reasonable rates of discharge. Comparisons to other battery systems at equivalent currents and rates are presented. The persulfate cell is seen as a potentially useful reserve battery for either high or low rates~ Water-activated batteries were rapidly developed during the 1940's when there was specific need for long shelf-life, higher power, reserve systems. The impetus for development came from military applications (1, 2). An early result of the intensive work done to develop such new energy sources was the silver chloridemagnesium reserve battery, which became commercially available in 1943 (3, 4). After 1946; applications for the AgC1/Mg battery grew rapidly and this system, despite its relatively high cost, became widely adopted. It has been used for weather baUons, air-sea rescue equipment, and sonobuoys, the latter application having accounted for a major fraction of production.The cuprous chloride-magnesium reserve battery (Cu2C12/Mg) first became commercially available in 1949 (5, 6). Like the AgC1/Mg battery, it is a long shelf-life, water or seawater activated unit. It is not suitable for the same kinds of use as the AgC1/Mg battery, having lower rate capability and, generally, lower energy density.The high cost of silver and the lower rate capabilities of Cu2C12 have led to considerable effort to find other systems suitable to replace the AgC1/Mg system. A number of water-activated systems appeared in the 1970's and deserve mention. Aluminum/ai?" battery.--The Furukawa BatteryCompany, Limited, of Tokyo introduced an aluminum/ air battery in 1969 (7). It consisted of a series of closed cells containing KOH pellets and utilized a 2.54 mm thick aluminum anode and a 3.38 mm thick, porous carbon, air breathing cathode. The battery was a fivecell device activated with water poured into one cell, which then filled all five subunits through overflow connections. Sold as a low rate (0.3A) battery, this system did not fulfill its advertised energy density goals. Moreover, though sealed in water-vapor resistant PET-plastic film bags, the KOH deteriorated after 5-6 months of storage.Cuprous ~2uoride/magnesium.--This cell system, Cu2F2/Mg (AZ-31) is a retained electrolyte cell of tea-* Electrochemical Society Active Member.1 Present address: Institute of Gas 'l~eehnology, Chicago, Illinois 60616.Key words: magnesium electrodes, persulfatesj water-activated batteries.sonably high power density (8). It was not, in the configurations tested here, a water-activated battery, but car...