Alkaline battery - AbsoluteAstronomy.com

Alkaline batteries are a type of primary batteries dependent upon the reaction between zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

and manganese dioxide (Zn

Zinc

/Mn

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

₂). A rechargeable alkaline battery

Rechargeable alkaline battery

Rechargeable alkaline battery is a type of alkaline battery that is rechargeable. The first generation rechargeable alkaline technology was developed by Battery Technologies Inc in Canada and licensed to Pure Energy, EnviroCell, Rayovac, and Grandcell...

allows reuse of specially designed cells.

Compared with zinc-carbon batteries

Zinc-carbon battery

A zinc–carbon dry cell or battery is packaged in a zinc can that serves as both a container and negative terminal. It was developed from the wet Leclanché cell . The positive terminal is a carbon rod surrounded by a mixture of manganese dioxide and carbon powder. The electrolyte used is a paste of...

of the Leclanché or zinc chloride types, alkaline batteries have a higher energy density

Energy density

Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...

and longer shelf-life, with the same voltage. Button cell

Button cell

A watch battery or button cell is a small single cell battery shaped as a squat cylinder typically 5 to 12 mm in diameter and 1 to 6 mm high—like a button on a garment, hence the name. Button cells are used to power small portable electronics devices such as wrist watches, pocket...

silver-oxide batteries

Silver-oxide battery

A silver oxide battery , not to be confused with a similar but different silver–zinc battery, which is a secondary cell, is a primary cell with relatively very high energy/weight ratio. They are costly due to the high price of silver...

have higher energy density and capacity but also higher cost than similar-size alkaline cells.

The alkaline battery gets its name because it has an alkali

Alkali

In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...

ne electrolyte of potassium hydroxide

Potassium hydroxide

Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...

, instead of the acidic ammonium chloride or zinc chloride electrolyte of the zinc-carbon batteries. Other battery systems also use alkaline electrolytes, but they use different active materials for the electrodes.

Alkaline batteries account for 80% of manufactured batteries in the US and over 10 billion individual units produced worldwide. In Japan alkaline batteries account for 46% of all primary battery sales. In Switzerland alkaline batteries account for 68%, in the UK 60% and in the EU 47% of all battery sales including secondary types.

History

The alkaline dry battery was invented by Canadian engineer Lewis Urry

Lewis Urry

Lewis Frederick Urry, , was a Canadian chemical engineer and inventor. He invented both the alkaline battery and lithium battery while working for the Eveready Battery company....

in the 1950s while working for the Eveready Battery company.
On October 9, 1957, Lewis Urry

Lewis Urry

Lewis Frederick Urry, , was a Canadian chemical engineer and inventor. He invented both the alkaline battery and lithium battery while working for the Eveready Battery company....

, Karl Kordesch

Karl Kordesch

Karl Kordesch was an Austrian chemist and inventor, most notable for jointly inventing the alkaline battery.-Life:...

, and P.A. Marsal filed US patent (2,960,558) for the alkaline battery. It was granted in 1960 and was assigned to Union Carbide

Union Carbide

Union Carbide Corporation is a wholly owned subsidiary of The Dow Chemical Company. It currently employs more than 2,400 people. Union Carbide primarily produces chemicals and polymers that undergo one or more further conversions by customers before reaching consumers. Some are high-volume...

Corporation.

Chemistry

In an alkaline battery, the anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

(negative terminal) is made of zinc

Zinc

powder, which gives more surface area for increased current, and the cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

(positive terminal) is composed of manganese dioxide. Unlike zinc-carbon (Leclanché

Leclanché cell

Georges Leclanché invented and patented his battery, the Leclanché cell, in 1866. The battery contained a conducting solution of ammonium chloride, a cathode of carbon, a depolarizer of manganese dioxide, and an anode of zinc...

) batteries, the electrolyte

Electrolyte

In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

is potassium hydroxide

Potassium hydroxide

rather than ammonium chloride

Ammonium chloride

Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...

or zinc chloride

Zinc chloride

Zinc chloride is the name of chemical compound with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. ZnCl2 itself is hygroscopic and even deliquescent. Samples should therefore be protected from...

.
The half-reactions are:

Zn (s) + 2OH⁻ (aq) → ZnO (s) + H₂O (l) + 2e⁻

2MnO₂ (s) + H₂O (l) + 2e⁻ →Mn₂O₃ (s) + 2OH⁻ (aq)

Capacity

Capacity of an alkaline battery is greater than an equal size Leclanché cell

Leclanché cell

or zinc-chloride cell because the manganese dioxide anode material is purer and denser, and space taken up by internal components such as electrodes is less. An alkaline cell can provide between three and five times capacity.

The capacity of an alkaline battery is strongly dependent on the load. An AA

AA battery

An AA battery is a standard size of battery. Batteries of this size are the most commonly used type of in portable electronic devices. An AA battery is composed of a single electrochemical cell...

-sized alkaline battery might have an effective capacity of 3000 mAh

MAH

The National Security Service was the governmental intelligence organization of Turkey between 1926 and 1965, when it was replaced by the National Intelligence Organization ....

at low drain, but at a load of 1 ampere

Ampere

The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...

, which is common for digital cameras, the capacity could be as little as 700 mAh. The voltage of the battery declines steadily during use, so the total usable capacity depends on the cut-off voltage

Cutoff voltage

In electronics, the cutoff voltage is the voltage at which a battery is considered fully discharged, and it is good practice to stop discharge at this point...

of the application. Unlike Leclanche cells, the alkaline cell delivers about as much capacity on intermittent or continuous light loads. On a heavy load, capacity is reduced on continuous discharge compared with intermittent discharge, but the reduction is less than for Leclanche cells.

Voltage

The nominal voltage of a fresh alkaline cell is 1.5 V. Multiple voltages may be achieved with series of cells.
The effective zero-load voltage of a non discharged alkaline battery varies from 1.50 to 1.65 V, depending on the purity of the manganese dioxide used and the contents of zinc oxide in the electrolyte. The average voltage under load depends on discharge and varies from 1.1 to 1.3 V. The fully discharged cell has a remaining voltage in the range of 0.8 to 1.0 V.

Current

The amount of current an alkaline battery can deliver is roughly proportional to its physical size. This is a result of decreasing internal resistance as the internal surface area of the cell increases. A general rule of thumb is that an AA alkaline battery can deliver 700 mA without any significant heating. Larger cells, such as C and D cells, can deliver more current. Applications requiring currents of several amperes, such as powerful flashlight

Flashlight

A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...

s and portable stereos, will require D-sized cells to handle the increased load.

Construction

Alkaline batteries are manufactured in standardized cylindrical forms interchangeable with zinc-carbon batteries, and in button forms. Several individual cells may be interconnected to form a true "battery", such as those sold for use with flashlights and the 9 volt transistor-radio battery.

A cylindrical cell is contained in a drawn steel can, which is the cathode connection. The cathode mixture is a compressed paste of manganese dioxide with carbon powder added for increased conductivity. The paste may be pressed into the can or deposited as pre-molded rings. The hollow center of the cathode is lined with a separator, which prevents mixing of the anode and cathode materials and short-circuiting of the cell. The separator is made of a non-woven layer of cellulose or a synthetic polymer. The separator must conduct ions and remain stable in the highly alkaline electrolyte solution.

The anode is composed of a dispersion of zinc powder in a gel containing the potassium hydroxide electrolyte. To prevent gassing of the cell at the end of its life, more manganese dioxide is used than required to react with all the zinc.

When describing standard AAA, AA, C, sub-C and D size cells, the anode is connected to the flat end while the cathode is connected to the end with the raised button.

Recharging of alkaline batteries

Some alkaline batteries are designed to be recharged (see rechargeable alkaline battery

Rechargeable alkaline battery

), but most are not. Attempts to recharge may cause rupture, or the leaking of hazardous liquids which will corrode the equipment.

Leaks

Alkaline batteries are prone to leaking potassium hydroxide

Potassium hydroxide

, a caustic agent that can cause respiratory, eye and skin irritation This can be avoided by not attempting to recharge disposable alkaline cells, not mixing different battery types in the same device, replacing all of the batteries at the same time, storing in a dry place, and removing batteries for storage of devices.

Once a leak has formed due to corrosion of the outer steel shell, potassium hydroxide forms a feathery crystalline structure that grows and spreads out from the battery over time, following up metal electrodes to circuit boards where it commences oxidation of copper tracks and other components, leading to permanent circuitry damage.

The leaking crystalline growths can also emerge from seams around battery covers to form a furry coating outside the device, that corrodes any objects in contact with the leaking device.

Disposal

When introduced in the 1960s, alkaline batteries contained a small amount of mercury amalgam

Amalgam (chemistry)

An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

to control side reactions at the zinc cathode. Improvements in the purity and consistency of materials have allowed manufacturers to reduce the mercury content in modern cells.
Unlike other types of batteries, alkaline batteries are allowed to be disposed of as regular domestic waste in some locations. This, however, may not be environmentally friendly

Environmentally friendly

Environmentally friendly are terms used to refer to goods and services, laws, guidelines and policies claimed to inflict minimal or no harm on the environment....

, as some alkaline batteries produced before 1996 contain mercury. For example the state of California has deemed all batteries as hazardous waste when discarded, and has banned the disposal of batteries with other domestic waste.
In the US, one company shreds and separates the battery case metals, manganese and zinc.http://www.toxco.com/processes.html Another company mixes batteries in as a feedstock in steel making furnaces, to make low-grade steel such as rebar; the zinc fumes are recovered separately.http://www.batteryrecycling.com/Battery+Recycling+Process
In Europe battery disposal is controlled by the WEEE regulations, and as such alkaline batteries must not be thrown in with domestic waste. They should be disposed through local recycling

Battery recycling

Battery recycling is a recycling activity that aims to reduce the number of batteries being disposed as municipal solid waste. Batteries contain a number of heavy metals and toxic chemicals, their dumping has raised concern over risks of soil contamination and water pollution.-Battery recycling by...

stations/waste dumps. In the EU most stores that sell batteries are required by law to accept old batteries for recycling.

Applications

Alkaline batteries are used in many household items. This includes MP3 players, CD players, digital cameras, pagers, toys, lights, and radios, to name a few.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

Chemistry

Capacity

Voltage

Current

Construction

Recharging of alkaline batteries

Leaks

Disposal

Applications

See also

External links