Dry cell

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A dry cell is a galvanic electrochemical cell with a pasty low-moisture electrolyte. A wet cell, on the other hand, is a cell with a liquid electrolyte, such as the lead-acid batteries in most cars.

While a dry cell's electrolyte is not truly completely free of moisture and must contain some moisture to function, when it was first developed it had the advantage of containing no sloshing liquid that might leak or drip out when inverted or handled roughtly, making it highly suitable for small portable electric devices. By comparison, the first wet cells were typically fragile glass containers with lead rods hanging from the open top, and needed careful handling to avoid spillage. An inverted wet cell would almost certainly leak, while a dry cell would not. Lead-acid batteries would not achieve the safety and portability of the dry cell, until the development of the Gel Battery.

A common dry cell battery is the zinc-carbon battery, using a cell sometimes called the dry Leclanché cell, with a nominal voltage of 1.5 volts, the same nominal voltage as the alkaline battery (since both use the same zinc-manganese dioxide combination). Multiple cells are commonly connected in series within a single case or battery compartment within a device to form a dry battery (or dry cell battery) of greater voltage than is provided by one cell. A well known dry battery is the 9-volt "transistor radio battery" (PP3 battery) which is internally constructed of a standard stack of six carbon-zinc or alkaline cells, or else three lithium cells.

In 2005 the Columbia dry cell battery was designated an ACS National Historical Chemical Landmark in recognition of its "significant improvement over previous batteries, meeting consumer demand for a maintenance-free, durable, no-spill, inexpensive electrochemical power source."[1]

[edit] Structure

See also: Zinc-carbon battery

For the cheapest carbon-zinc variety, a zinc outer casing (anode) contains a layer of NH₄Cl with ZnCl₂ aqueous paste separated by a paper layer from a mixture of powdered carbon & [[manganese(IV) oxide]=] (MnO₂) which is packed around a carbon rod (cathode). As the cell runs, manganese is reduced from an oxidation state of +4 to +3, collecting electrons from the carbon rod, while the zinc metal anode is oxidized to Zn²⁺ ions, producing the electrons. So the electrons travel outside the cell, from the zinc casing (the negative end or anode) through contacts and wires to the carbon rod (which is in contact with the manganese dioxide powder, the actual cathode material, and so is positive).

In so-called alkaline cells (see alkaline battery), some of the electrolyte in the paste is replaced with an alkaline paste of potassium hydroxide. However, the essential transfer of electrons from zinc to manganese still powers the cell.

The standard carbon-zinc dry cell is relatively cheap, and until recently, has been the most common type of cell (only recently being replaced in most uses by the alkaline type). It was the first commercial portable battery (technically, a battery is made of two or more cells) and therefore the dry cell had a large impact on society, as it contributed to the development of flashlights (torches) and portable radios.

[edit] Timeline of portable battery cell invention history

• 1800 - Alessandro Volta invents the voltaic pile and discovers the first practical method of generating low voltage high current electricity. Constructed of alternating discs of zinc and copper with pieces of leather soaked in brine between the metals, the voltaic pile is the first "wet cell battery."
• 1836 - Englishman, John Frederic Daniell invented the Daniell cell that used two electrolytes: copper sulfate and zinc sulfate. The Daniel Cell is safer and less corrosive then the Volta cell.
• 1859 - French inventor, Gaston Planté developed the first practical storage lead-acid battery that could be recharged (secondary battery). This type of battery is primarily used in cars today.
• 1866 - French engineer, Georges Leclanché patented the carbon-zinc wet cell battery called the Leclanché cell. It is assembled in a porous pot. The positive electrode consists of crushed manganese dioxide with a little carbon mixed in. The negative pole is a zinc rod. The cathode is packed into the pot, and a carbon rod was inserted to act as a current collector. The anode or zinc rod and the pot were then immersed in an ammonium chloride solution. The liquid acted as the electrolyte, readily seeping through the porous cup, acting as electrolyte, and making contact with the cathode material.
• 1868 - Twenty thousand of Georges Leclanche's cells were now being used with telegraph equipment.
• 1881 - J.A. Thiebaut patents the first battery with both the negative electrode and porous pot placed in a zinc cup.
• 1885 - Japanese clockmaker, Sakizou Yai invented the first dry cell battery.
• 1887 - Frederik Louis Wilhelm Hellesen invents the first dry cell battery based on Leclanché's design.
• 1887 - Carl Gassner invented the first commercially successful dry cell battery (zinc-carbon cell). It is very similar to the wet cell design, but simply with less water in the paste, and with the entire assembly sealed water-tight.
• 1899 - Waldmar Jungner invents the first nickel-cadmium rechargeable battery.
• 1901 - Thomas Edison invents the alkaline storage battery.
• 1949 - Lewis Urry invents the small alkaline battery.

[edit] Modern alkaline battery (cell)

Lewis Urry developed the small alkaline battery in 1949, working for the Eveready Battery Co. at their research laboratory in Parma, Ohio. Alkaline batteries use a different electrolyte, and last five to eight times as long as zinc-carbon cells, their predecessors. At the time, this was not considered patentable invention.