Why Is Zinc Used in Batteries?

Alkaline batteries produce 1.5 volts due in part to their zinc anodes.

The first battery, designed and built by Alessandro Volta in 1799, incorporated zinc metal as the anode and copper metal as the cathode. The use of zinc in batteries persists today. Modern alkaline batteries use zinc as their anode and manganese dioxide as their cathode material. Other batteries incorporating zinc include the zinc-mercury oxide batteries, commonly used in hearing aids, and the silver-zinc batteries, usually reserved for aeronautical applications.

Battery Basics

All batteries share three common components: an anode, a cathode and an electrolyte. The anode supplies electrons, through whatever device the battery is powering, to the cathode. This process, however, results in a charge imbalance in the electrodes, which the electrolyte corrects by allowing negative particles called anions to flow to the anode and positive particles called cations to flow to the cathode.

Oxidation and Reduction

All of the processes taking place in a battery represent chemical reactions. Zinc, as an anode, gives up electrons in a process called oxidation. The cathode material accepts the electrons in a process called reduction. These processes always occur in conjunction, and chemists refer to them collectively as "redox" reactions. The ability of a material to donate or accept electrons varies from one material to the next. Chemists quantify this tendency to donate or accept electrons with redox potentials.

Redox Potentials

Chemists measure reduction potentials relative to the tendency of hydrogen to accept electrons. That is, the reaction in which two positively charged hydrogen atoms gain electrons to form hydrogen gas is assigned a potential of zero volts. All other materials either exhibit a greater tendency to accept electrons and thus generate redox potentials more positive than hydrogen, or they exhibit a weaker tendency to accept electrons than hydrogen and thus generate negative redox potentials. The voltage produced by an electrochemical cell reflects the difference between these potentials for the anode and cathode. In the case of an alkaline battery, the redox potentials between zinc and manganese dioxide sum to about 1.5 V, which represents the voltage produced by the battery.

Zinc and Batteries

Most of the benefits of incorporation of zinc in a battery relate to its favorable electrochemistry, i.e. its ability to donate electrons, and its relative stability. Many metals would technically produce a higher voltage in a battery than zinc because they more easily donate electrons. But above a certain point, the ability to donate electrons becomes problematic. Sodium metal, for example, will donate electrons to water, which means it would react with the battery's electrolyte. Aluminum tends to easily form oxide coatings on its surface, which would inhibit its performance. Zinc benefits from one other significant advantage in that, as a raw material, it is inexpensive.

References

• Montclair State University, College of Humanities and Social Sciences: Early Batteries...
• Nassau Community College: Batteries
• University of Washington, Dept. of Materials Science & Engineering Education: How Do Batteries Work?
• College of St. Benedict, St. John's University: Oxidation/Reduction (Redox) Reactions
• Georgia State University, Dept. of Physics: Oxidation-Reduction Potentials
• University of Hawaii: The "Dry-Cell" Battery

Resources

• Purdue University, Dept. of Chemistry: Electrochemical Reactions
• Northwestern University: Power System: How Do Batteries Work?