Cell voltage nickel iron

Because the nickel—iron cell system has a low cell voltage and high cost compared to those of the lead—acid battery, lead—acid became the dorninant automotive and industrial battery system except for heavy-duty appHcations. Renewed interest in the nickel—iron and nickel—cadmium systems, for electric vehicles started in the mid-1980s using other cell geometries. 

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 ( )...

The electrochemical equivalent of iron (if only the first step is taken into account) is 960 Ah/kg and the open-circuit voltage of the nickel/iron cell is 1.4 V. 

Potassium manganate obtained above is oxidized to the permanganate either by electrolysis or by chemical oxidation. Electrolytic oxidation is more common. Electrolytic cells have cathodes made of iron rods and nickel-plated anodes. Potassium manganate melt is extracted with water prior to its electrolysis and then electrolyzed at a cell voltage of 2.3V and current of about 1,400 amp. Permanganate is produced at the anode and water is reduced to gaseous hydrogen and hydroxyl ions at the cathode ... 

INCO produced electrolytic nickel at its refinery in Port Colborne, Ontario, Canada. The production started in 1926. The anodes were made by reducing nickel oxide with coke, and the anodes contained about 93.5% Ni, 4% Cu, and 1% Co. The sulfur content was low, about 0.6%. The approximate composition of the purified electrolyte was 60 g L-1 Ni2+, 95 g L-1 S042-, 35 g L-1 Na+, 55 g L-1 Cl , and 16 g L 1 boric acid, and the temperature was 60 °C. The current density of the process was 16 A/sq.ft (approximately 170 A m-2) and the cell voltage was about 1.6 V. At the normal cell operating voltage, the principal impurities - iron, cobalt, lead, arsenic, and copper - dissolved into the solution with nickel. Silver, gold, the PGMs, sulfur, selenium, and tellurium fell to the bottom of the cell as an insoluble slime. The produced cathodes... 

The INCO, Thompson plant in Manitoba, Canada, electrolyzes 240 kg sulfide anodes in a sulfate-chloride electrolyte. The approximate composition of the electrolyte is 60 g L x Ni2+, 95 g L 1 SC>42, 35 g L 1 Na+, 60 g L 1 Cl-, and 16 g L 1 H3BO4, and the temperature is 60 °C. Nickel, cobalt, and copper dissolve from the anode, while sulfur, selenium, and the noble metals form an insoluble sludge or slime, from which they can be recovered. The anode sludge contains 95% elemental sulfur, sulfide sulfur, nickel, copper, iron, selenium, and precious metals. Nickel is deposited on to pure nickel starting sheets. The anode cycle is 15 days and the cathode cycle is 5 to 10 days. Electrolysis is carried out at a current density of 240 A m-2 giving a cell voltage of 3 to 6 V [44, 46]. 

Alkaline electrolytes offer further advantages over acidic electrolytes. Oxygen reduction is considerably faster in alkaline electrolytes, which implies that the working potential of the oxygen electrode is more positive, and a larger cell voltage can be realized. Also, apart from the advantages in catalyst selection, less severe corrosion conditions allow nickel and alloys of iron to be used as structural materials in AFCs. 

Ferrous iron in the anolyte is oxidized to Fe " by dissolved chlorine. Since the solubility product of ferric hydroxide is very small ( 10 ), iron deposits on the membrane surface before it can penetrate the membrane. Iron, therefore, does not affect the selectivity of the membrane but may increase the voltage drop by reducing the effective area. Nickel has similar effects. Iron is generally less harmful because of very low solubility. However, it was reported [109] that in the presence of iron contamination, the current efficiency of Asahi Chemical cells with Aciplex membranes decreased by 2%. The cell voltage, on the other hand, was unaffected over 50 months of operation. The source of the iron was potassium ferrocyanide, an anticaking agent in the evaporated salt used as the raw material. 

Thomas Alva Edison invented the alkaline nickel-iron battery at the beginning of the 20 century. Iron is the negative pole, nickel oxide the positive. One cell has a voltage of 1.15 V. Several cells, connected in series, were used in industrial applications and for emergency power. The battery Hfe was restricted to about 10 years. 

Types of Batteries. The two primary types of batteries used are lead-acid and nickel-iron-alkaline. A lead-acid battery will provide 2.0 to 2.3 V per cell, while the nickel-iron-alkaline battery will provide 1.2 V per cell. Voltages used for modern battery-powered mobile equipment are 12,24,36,48, and 72, with some higher voltages used in larger equipment. 

The average cell voltage of 1.2 V is slightly lower than that of the Edison cell. Cadmium is preferred to iron in the nickel-aUcaline cell because cadmium hydroxide is more conductive than iron hydroxide. The absence of higher oxidation states for cadmium minimizes side reactions, which occur in the Edison cell. The nickel-cadmium cell can also be charged at a lower voltage since there is no overvoltage, as there is at the iron electrode. 

The first systems to be examined are the nickel/iron and the nickel/zinc systems. Values ranging from 60 to 80kWh/kg seem realizable, without regard to life expectancy. The nickel/iron and nickel/zinc systems will always be more expensive than a comparable lead-acid battery for the following three reasons the materials involved are more expensive, the production involves more expenditure, which is partly the case because a greater number of cells are required for the same voltage, and more cells are needed because each cell yields less voltage. So to be more... 

FIGURE 25.5 Effect of decreasing rate on battery voltage of nickel-iron cell. 

FIGURE 25.6 Time-voltage discharge curves of nickel-iron battery end voltage 1.0 V per cell. From Ref. 9.)... 

FIGURE 25.8 Hours of service of nickel-iron battery at discharge rates and temperatures end voltage 1.0 V cell. 

The battery is less damaged by repeated deep discharge than any other battery system. In practice, an operator will drive a battery-operated vehicle until it stalls, at which point the battery voltage is a fraction of a volt per cell (some cells may be in reverse). This has a minimal effect on the nickel-iron battery in comparison with other systems. 

Figure 4.12 shows the voltage profile for a single nickel-iron cell tested to the constant current modes as indicated. 

---