Page 40 - Lindens Handbook of Batteries
P. 40

BASIC CONCEPTS       1.15

                                     10000
                                                                                   Theoretical specific energy
                                                                                   active materials
                                                                                   Theoretical specific energy
                                                                                   practical battery
                                                                                   Actual specific energy
                                    Specific energy (Wh/kg)  100
                                     1000













                                       10            Zinc/air
                                             Leclanche dry cell  Alkaline/MnO 2  Lithium/MnO 2  Lithium/SO 2  Lead-acid  Nickel-cadmium  Nickel-metal hydride  Lithium-ion







                                               Primary batteries  Rechargeable batteries
                                  FIGURE 1.4  Theoretical and actual specific energy of battery systems.


                                   In Fig. 1.4, the following values for some major batteries are plotted:
                                1.  The theoretical specific energy (based on the active anode and cathode materials only)
                                2.  The theoretical specific energy of a practical battery (accounting for the electrolyte and nonreactive
                                  components)
                                3.  The actual specific energy of these batteries when discharged at 20°C under optimal discharge
                                  conditions
                                   These data show:

                                •  That the weight of the materials of construction reduces the theoretical energy density of the bat-
                                  tery by almost 50%, and
                                •  That the actual energy delivered by a practical battery, even when discharged under conditions
                                  close to optimum, may only be 50 to 75% of that lowered value
                                The development of “pouch cells” which use foil-laminate packaging has significantly reduced the
                                weight and volume penalty associated with the container. (See Chapters 26 and 27.)
                                   Thus, the actual energy that is available from a battery under practical, but close to optimum,
                                discharge  conditions  is  only  about  25  to  35%  of  the  theoretical  energy  of  the  active  materials.
                                Chapter 3 covers the performance of batteries when used under more stringent conditions.
                                   These data are shown again in Table 1.2 which, in addition to the theoretical values, lists the char-
                                acteristics of each of these batteries based on the actual performance of a practical battery. Again,
                                these values are based on discharge conditions close to optimum for that battery.
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