BATTERY CHEMISTRY—PART 1
Regardless of type, size or shape, all batteries operate on the same principal: a chemical reaction between two electrodes in the presence of an electrolyte. The metals can be solid or powdered, and the electrolyte can be liquid, aqueous paste or gel.
Early batteries and the typical automotive battery today are known as “wet cell” batteries due to the electrolyte being in a free-flowing liquid state. The electrolyte in so-called “dry cell” batteries is still in a liquid form but is suspended in a powdered matrix, and only enough is used to moisten the mix.
Many primary batteries use zinc as the negative electrode (anode) and manganese dioxide as the positive electrode (cathode).
Zinc-carbon (and zinc-chloride) batteries have an outer shell of zinc. An inert carbon rod acting as the cathode, suspended in the manganese dioxide powder that surrounds the carbon rod, is the electrolyte—an acidic aqueous paste of ammonium chloride (or zinc chloride). The zinc-carbon battery was the first dry cell and is still in production in many popular sizes, including AAA, AA, C and D cells, and 6-volt lantern batteries. The nominal voltage is 1.5 volts per cell; the 6-volt battery uses four cells connected in series (end to end, positive to negative).
Alkaline batteries use the same zinc and manganese dioxide electrode theme, but the electrolyte is an alkali paste containing potassium hydroxide. The chemical reaction inside an alkaline battery produces much more electrical power than does a zinc-carbon cell of the same size, giving it the capability to power devices that require higher current than the acidic battery can muster while maintaining the same nominal 1.5 volts. Alkaline batteries also have a much longer shelf life in storage than zinc-carbon or zinc-chloride batteries. Alkaline batteries can be used in devices suitable for non-alkaline cells of the same size and will provide much longer runtime before depletion.
Using the popular AA battery as an example, we can get an idea of how much difference battery chemistry can make: Non-rechargeable zinc–carbon AA batteries have around 400 to 900 milliampere hours (mah) of capacity. Zinc–carbon batteries are usually marketed as "general purpose" batteries. Zinc-chloride batteries store around 1,000 to 1,500 mah and are often sold as "heavy duty" or "super heavy duty." Alkaline AA batteries have a capacity from 1,700 to 2,850 mah.
Non-rechargeable lithium iron disulfide batteries are manufactured for devices that use a lot of power (such as digital cameras), where their high cost is offset by longer runtime between battery changes and more-constant voltage during discharge. Lithium iron disulfide batteries are intended for use in devices compatible with alkaline zinc batteries of the same physical size. Depending on the design and materials used, these disposable batteries are available in cell voltages from 1.5V (comparable to alkaline zinc) up to 3.7V. Lithium iron disulfide batteries can have a very long shelf life.