A silver zinc battery is a secondary cell that utilizes silver(I,III) oxide and zinc.

Overview

Silver zinc cells share most of the characteristics of the silver-oxide battery, and in addition, is able to deliver one of the highest specific energies of all presently known electrochemical power sources. Long used in specialized applications, it is now being developed for more mainstream markets, for example, batteries in laptops and hearing aids. Silver–zinc batteries, in particular, are being developed to power flexible electronic applications, where the reactants are integrated directly into flexible substrates, such as polymers or paper, using printing or chemical deposition methods. Experimental new silver–zinc technology (different to silver-oxide) may provide up to 40% more run time than

lithium-ion batteries A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also se ...

and also features a water-based chemistry that is free from the thermal runaway and flammability problems that have plagued the lithium-ion alternatives.

Chemistry

The silver–zinc battery is manufactured in a fully discharged condition and has the opposite electrode composition, the cathode being of metallic silver, while the anode is a mixture of zinc oxide and pure zinc powders. The electrolyte used is a potassium hydroxide solution in water. During the charging process, silver is first oxidized to silver(I) oxide : 2 Ag(s) + 2 OH⁻ → Ag₂O + H₂O + 2 e⁻ and then to

silver(II) oxide Silver(I,III) oxide or tetrasilver tetroxide is the inorganic compound with the formula Ag4O4. It is a component of silver zinc batteries. It can be prepared by the slow addition of a silver(I) salt to a persulfate solution e.g. AgNO3 to a Na2S ...

: Ag₂O + 2 OH⁻ → 2 AgO + H₂O + 2 e⁻, while the zinc oxide is reduced to metallic zinc : 2 Zn(OH)₂ + 4 e⁻ 2 Zn + 4 OH⁻. The process is continued until the cell potential reaches a level where the decomposition of the electrolyte is possible at about 1.55 volts. This is taken as the end of a charge, as no further charge is stored, and any oxygen that might be generated poses a mechanical and fire hazard to the cell.

History and usage

This technology had the highest

energy density In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the ''useful'' or extract ...

prior to lithium technologies. Primarily developed for aircraft, they have long been used in space launchers and crewed spacecraft, where their short cycle life is not a drawback. Non-rechargeable silver–zinc batteries powered the first Soviet

Sputnik Sputnik 1 (; see § Etymology) was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for t ...

satellites, as well as US

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

launch vehicles, the

Apollo Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...

, lunar rover and life-support backpack. The primary power sources for the command module (CM) were the hydrogen/oxygen

fuel cells A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

in the service module (SM). They provided greater energy densities than any conventional battery, but peak-power limitations required supplementation by silver–zinc batteries in the CM that also became its sole power supply during re-entry after separation of the service module. Only these batteries were recharged in flight. After the

Apollo 13 Apollo 13 (April 1117, 1970) was the seventh crewed mission in the Apollo space program and the third meant to land on the Moon. The craft was launched from Kennedy Space Center on April 11, 1970, but the lunar landing was aborted aft ...

near-disaster, an auxiliary silver–zinc battery was added to the service module as a backup to the fuel cells. The Apollo service modules used as crew ferries to the Skylab space station were powered by three silver–zinc batteries between undocking and service module jettison, as the hydrogen and oxygen tanks could not store fuel-cell reactants through the long stays at the station. These cells are found in applications for the military, for example in Mark 37 torpedoes or on Alfa-class submarines.

References

{{Galvanic cells Disposable batteries Metal oxide–zinc batteries

Overview

Chemistry

History and usage

See also

References