A Lithium-Powered Heart The cardiac pacemaker is amodern miracle of science that many of us take for granted-hut not a person who owns one! These pacemakers operate on hattery power, and the demands put on the tins hatteries that generate it are awesome! They must start the human machine every morning without fail, and the human lights and radio are running all the time. Yet many, many people are adding healthy years to life by betting on the chemical reactions that occur in these batteries to generate-day in, day out-the electric current that drives their pacemakers. These hatteries have special requirements because they must be implanted in a human body. They must he rugged and leakproof, have long life and minimal weight, and, of course, they must be nontoxic. The first hatteries used in pacemakers had a lifespan of only 2 years, and the periodic operations required for replacement meant additional risk and stress for the patient. Chemists began to tackle this problem, and research efforts in electrochemistry uncovered lithium metal, a new substance with the potential to give long life to hatteries. Unfortunately, lithium is highly reactive-it burns in air and reacts with water to produce flammable hydrogen gas. If lithium were to he used, i t would he necessary to discover new. nonaaueous electrolvte svstems. ~iectrolytesare suhstances'that dissolve in water t o form conductina solutions. Thev dissolve to nroduce ions. narticles carrying electrical charge. The movement of 'these charges carries the current as the batterv's chemistrv releases its stored energy. Conventional hatteries that draw on the chemical energy of zinc and mercuric oxide depend upon
844
Journal of Chemical Education
aqueous electrolytes. So the problem for the chemists to solve was defined-to design a battery that would operate without water. Extensive investigations into new solvents and new materials for use in high energy, long-life hatteries eve~tuallyled t o the discovery of a solid electrolyte for use with lithium metal. The solid electrolyte is iodine, and the lithinm-iodine battery was horn for biomedical applications. These revolutionary hatteries are currently in use, and they have an impressive lifespan of 10 years! The benefits to those who must depend upon cardiac pacemakers are incalculable. The lithium-iodine battery is not the end of the story. I t is a vast improvement over its predecessors and extremely useful in pacemakers, hut i t has a lower power than would he optimum for other uses. On the horizon is the need for new, higher-power hatteries for use in other implantable organs like artificial kidneys and hearts. But further electrochemical research will undoubtedly provide the answer. I t has in the past, and it will again.
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These short vignettes are taken from,"Opportunities in Chemistry", copyright 1985 by the National Academy of Sciences end repro. dumd with i b permission. This comprehensive report on future diretions and goals for chemical research contains much informatian both on chemistry and manpower and education that is of use to the teacher; these vignehes are being reproduced bemuse of their obvl0"s wide utility in the classroom. The full report can be purchasedf a $28.50 clothbound and $18.50 paperbound from: National Academy Press. 2101 Gonsliiution Avenue, NW, Washinglon. DC 20418. A quantitydiscoumof 15%for 5-24 copies end 25% f a 25-499 copies is available; all orders must be prepaid.
