108 Electricity & Electronics Panasonic Battery Sales Division Figure 7-5. Theoretical energy densities of lithium batteries compared with conventional batteries. Theoretical Energy Densities Lithuium Batteries Reaction E (Wh/kg) Battery Type nLi + (CF)n nLiF + nC 3.20 2,260 Polycarbonmonofl uoride lithium battery 8Li + 3SOCI2 6LiCl + Li2SO3 + 2S 3.61 1,877 Thionyl chloride lithium battery 2Li + CuF2 2LiF + Cu 3.54 1,646 ____________ 2Li + NiF2 2LiF + Ni 2.83 1,370 ____________ 2Li + 2SO2 Li2S2O4 2.95 1,114 Sulfur dioxide lithium battery 2Li + 2MnO2 Li2O + Mn2O3 2.69 768 Manganese dioxide lithium battery 2Li + Ag2CrO4 Li2CrO4 + 2Ag 3.35 520 Silver chromate lithium battery Conventional Batteries Reaction E (Wh/kg) Battery Type Zn + 2MnO2 Zn2– + 2MnOOH 1.70 234 Zinc-carbon battery Zn + HgO Zn(OH)42– 1.40 266 Mercury battery Zn + Ag2O ZnO + 2Ag 1.60 287 Silver-oxide battery Mercury Cell Th e mercury cell shown in Figure 7-4 creates a voltage of 1.34 volts from the chemical action between zinc (–) and mercuric oxide (+). However, the mercury cell creates about fi ve times more current than the conventional dry cell. It also maintains its terminal voltage under load for longer periods of operation. Th e mercury cell has found wide use in powering fi eld instruments and portable communications systems. Mercury cells may cause environmental and health issues, so its use is restricted. Lithium Cell Lithium has the highest negative potential of all metals. Many battery makeups are possible by mixing lithium with various substances. Energy densities of these batteries can be computed by respective reaction equations. Figure 7-5 shows the energy densities of lithium batteries compared with those of conventional batteries. Lithium is suitable for production of high voltage and lightweight batteries. Refer to Figure 7-6. Lithium batteries have a long life and are used in many implantable medical devices. Features of lithium batteries, such as voltage and discharge capacity, are determined by the type of substance used. Fluorocarbon is an intercalation (inserted between or among existing elements) compound. It is produced through reaction of carbon powder and fl uorine gas. Silver-Oxide Cell Silver-oxide cells have several advantages over other types of cells. Th ese advantages include: ■ Very stable discharge voltage. ■ Excellent high discharge characteristics. Electrolyte absorbent material Anode cylinders (4) Outer steel case Vent area Insulator spacer Depolarizer cylinders (3) Inner steel case Tin-plated steel inner top Nickel-plated steel outer top Panasonic Battery Sales Division Figure 7-4. Mercury cell. It creates voltage by chemical action between zinc and mercuric oxide. Copyright Goodheart-Willcox Co., Inc.