ATMOSPHERIC (30 CI 



ELtCTBOLYTE 



_l I I I I L. 



ICI I 



70 > 



- 20 



— 10 



30 60 90 120 150 



210 240 270 300 330 360 390 420 460 



TIME (MINI 



Fig. 7.4 Silver-zinc cell discharge characteristics under high pressure. 

 (From Ret. (12)1 



Pressure 



In 1963, Home (9) stated that the effects of 

 pressure on battery performance should be 

 slight, and subsequent experience proved 

 this correct. More recently, Funao et al. (12) 

 performed a number of experiments on sil- 

 ver-zinc secondary batteries. One result of 

 their studies is shown in Figure 7.4 and 

 indicates that there is no appreciable differ- 

 ence in capacity at atmospheric pressure 

 than at 600 kg/cm^ (8,532 psi). The range of 



fluctuation in electrolyte level due to pres- 

 sure was found to be larger than the range 

 due to discharge and the electrolyte did not 

 regain its original level after pressure was 

 removed. The authors could not explain the 

 phenomenon and suggest further study of 

 this irreversible process. 



Summarizing Home's and others' observa- 

 tions and his own. Work (11) concluded that 

 pressure might well be beneficial to battery 

 performance by: 1) Increasing the electrolyte 

 conductivity (5 percent in Pb-acid; 2 percent 

 in Ag-Zn), 2) reducing the volume of any gas 

 at or in a porous electrode making more 

 electrolyte available at the surface and effec- 

 tively increasing current density, and 3) 

 through some unknown mechanism, increas- 

 ing the power and providing greater watt- 

 hour efficiency. 



Cell Life and Cycling 



For all practical purposes the life of a 

 secondary battery begins when the electro- 

 lyte is introduced. At this point the battery 

 is said to be activated and its useful longev- 

 ity is termed wet life or shelf life. In sub- 

 mersible operations a battery is charged be- 

 fore and after each dive, and its usefulness 



TABLE 7.4 CELL CHARACTERISTICS OF THREE BATTERY TYPES [FROM REF. (10)] 



Shelf life in charged condition 



Composition, 

 charged state 



Cell potential, V 



Time to discharge 



Life in operation 



Without 

 maintenance 



With 

 maintenance 



Battery type Fast- Slow- Shelf life if If 



Pos. Neg. Elec- Open Dis- est, Av., est, discharged Charge loss. Shelf charged Shelf Cycles Float 



trolyte circ. charging (min) (hr) (days) (wet) % life each: life 



Lead-acid... PbOj Pb HjSO^ 2.14 2.1-1.46 3-5 8 >3 Not per- Low-rate; Days 30-45 Years To 500 To 14 yr 



mitted 15-20%/yr Months days 



Nickel-cadmium.. N1O2 Cd KOH 1.34 1.3-0.75 5 5 >3 Years Pocket; Months 30-45 Years 100-2,000 8-14 yr 



20-40%/yr Weeks days 25-500 4-8 yr 



Sintered; 

 10-15%/mo 



Silver-zinc... AgO Zn KOH 1.86 1.65-1.1 <0.5 5 >90 Years 15-20%/yr 3-12 mo 6 mo 1-2yr 100-300 1-2yr 



low dis. 

 5-100 



high dis. 



SOURCE: F. D. Yeaple, Dry Cell Performance, /"/-orf. Eng., 36;160 (1965). 



322 



