BAT­TERY CHEM­ISTRY—PART 1

American Survival Guide - - FIRST WORDS -

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.

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