Nickel discharge

Electrodes. A number of different types of nickel oxide electrodes have been used. The term nickel oxide is common usage for the active materials that are actually hydrated hydroxides at nickel oxidation state 2+, in the discharged condition, and nickel oxide hydroxide [12026-04-9] NiO OH, nickel oxidation state 3+, in the charged condition. Nickelous hydroxide [12034-48-7J, Ni(OH)2, can be precipitated from acidic solutions of bivalent nickel... 

Some y-NiOOH has been shown to be formed in sintered nickel electrodes (38), and changes in water and KOH concentration during the cycling of nickel electrodes has been studied (12,39—41). Although there is some disagreement on the movement of water, KOH is adsorbed on the nickel electrode when the cell is charged and desorbed from the electrode when the cell is discharged. 

Lower cost and lower weight cylindrical cells have been made using plastic bound or pasted actwe material pressed into a metal screen. Tliese cells suffer slightly in utilization at high rates compared to a sintered-plate cylindrical cell, but they may be adequate for most applications. Tlie effect of temperature and discharge rate on the capacity of sealed nickel-cadmium cells is illustrated in Figure 8 and Table 3. 

Fig. 8. Discharge capacity of small sealed nickel—cadmium cells where the hiitial charge is 0.1 C x 16 h at 20°C and the discharge is 1 C at temperatures of...

Electrochemistry and Kinetics. The electrochemistry of the nickel—iron battery and the crystal stmctures of the active materials depends on the method of preparation of the material, degree of discharge, the age (Life cycle), concentration of electrolyte, and type and degree of additives, particularly the presence of lithium and cobalt. A simplified equation representing the charge—discharge cycle can be given as ... 

Siatered nickel electrodes used in nickel iron ceUs are usually thicker than those used in Ni/Cd ceUs. These result in high energy density ceUs, because very high discharge rates are usually not required. 

Fig. 10. Power and voltage characteristics of the nickel—iron cell where the internal resistance of the cell, R, is 0.70 mQ, at various states of discharge ( )...

Some efforts toward sealed battery development (76) were made. However, a third electrode, an oxygen recombination electrode was required to reduce the cost of the system. High rate appHcations such as torpedo propulsion were investigated (77) and moderate success achieved using experimental nickel—zinc ceUs yielding energy densities of 35 W-h/kg at discharge rates of 8 C. A commercial nickel—zinc battery is considered to be the most likely... 

Fig. 17. 50 A-h nickel—hydrogen performance showing (a) pressure and (b) voltage curves where region A represents charging at 10 A, region B represents overcharge at 10 A, region C represents discharge at 25 A, and region D represents reversal at 25 A. To convert MPa to psi, multiply by 145.

A number of manufacturers started commercial production of nickel—MH cells in 1991 (31—35). The initial products are "AA"-size, "Sub-C", and "C -size cells constmcted in a fashion similar to small sealed nickel —cadmium cells. Table 6 compares the Ovonics experimental cell and a similar sized nickel—cadmium cell. Ovonics also deUvered experimental electric vehicle cells, 22 A-h size, for testing. The charge—discharge of "AA" cells produced in Japan (Matsushita) are compared in Figure 22. 

From these data, the hydride cells contain approximately 30—50% more capacity than the Ni—Cd cells. The hydride cells exliibit somewhat lower high rate capabiUty and higher rates of self-discharge than nickel—cadmium cells. Life is reported to be 200—500 cycles. Though not yet in full production it has been estimated that these cells should be at a cost parity to nickel—cadmium cells on an energy basis. 

A. Charkey, "Nickel—Zinc Cells for Sustained High-Rate Discharge," Proceedings of the 7th Intersociety Pnerg Confersion Engineering Conference, 1972. 

Lateritic Ores. The process used at the Nicaro plant in Cuba requires that the dried ore be roasted in a reducing atmosphere of carbon monoxide at 760°C for 90 minutes. The reduced ore is cooled and discharged into an ammoniacal leaching solution. Nickel and cobalt are held in solution until the soflds are precipitated. The solution is then thickened, filtered, and steam heated to eliminate the ammonia. Nickel and cobalt are precipitated from solution as carbonates and sulfates. This method (8) has several disadvantages (/) a relatively high reduction temperature and a long reaction time (2) formation of nickel oxides (J) a low recovery of nickel and the contamination of nickel with cobalt and (4) low cobalt recovery. Modifications to this process have been proposed but all include the undesirable high 760°C reduction temperature (9). 

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