Silver–zinc: status of technology and applications

Abstract

Abstract Michel Yardney and Professor Henri Andre developed the first practical silver–zinc battery more than 55 years ago. Since then, primary and rechargeable silver–zinc batteries have attracted a variety of applications due to their high specific energy/energy density, proven reliability and safety, and the highest power output per unit weight and volume of all commercially available batteries. Although significant improvements have been achieved on traditional systems such as lead–acid and nickel/cadmium, and in spite of the advent of new electrochemistries such as lithium–ion and nickel/metal hydride, many users still rely on silver–zinc to satisfy their most demanding and critical requirements. Over the past few years, several of the internal components have been subject to many studies which resulted in significant improvements in the battery wet life and cycle life. Specifically, these include new separator materials which offer an alternative to the cellulosic membranes, improvements to the zinc electrode that include additives that help reduce shape-change and dendritic growth, and to a lesser extent, process changes to the silver electrode and additives to the electrolyte. In comparison, the commonly used secondary systems are lead–acid, nickel/cadmium, nickel/metal hydride, and lithium–ion. Each has attributes which make them desirable for certain applications. Where low cost, high voltage, and high rate capability is required, the lead–acid battery is an obvious choice whenever size and weight are not critical. For applications requiring longer wet life, moderate rate capability, and high cycle life, nickel/cadmium or nickel/metal hydride can be used in spite of their poor charge retention and higher costs. Relatively newer systems are also available such as lithium–ion or lithium polymer technology which are preferred for their high voltage and excellent cycle life. Among the disadvantages of these systems are higher costs, limited configurations (usually available in small cylindrical cells) and lack of an established data base. In spite of the advantages noted for the popular secondary systems, the silver–zinc couple still is the system of choice where high specific energy/energy density, coupled with high specific power/power density are important for high-rate, weight or size-sensitive applications. In the 1950s, Yardney developed the first practical rechargeable silver–zinc cell for an underwater application. The U.S. Navy, recognizing the potential of this system for torpedo propulsion, soon adopted it to power the majority of its electric torpedoes—increasing their speed and range, and allowing more room for increasing the performance capability of the torpedo. One of the first programmes which adopted the silver–zinc technology was the MK58 or `Brush' torpedo which consisted of 44 A h cells. At that time, silver–zinc batteries became the preferred system for many other applications. Some of the unique systems include the largest silver–zinc battery ever made, a 256-ton battery for the Albacore G-5 submarine. This battery consisted of a two-section, two-hundred-and-eighty-cell battery, with each cell rated at 20,000 A h. Each cell was essentially the size of a standard four-drawer filing cabinet. Since that time, many of the silver–zinc applications have considerably scaled down their power requirements. Underwater applications are consistently using the larger sized batteries while the smallest are typically found in missile applications. This paper will describe some of the current activities in addressing the major components of the cell and a summary of the current applications of the silver–zinc system.