Electrodes sintered-nickel

The other type of nickel electrode involves constmctions in which the active material is deposited in situ. This includes the sintered-type electrode in which nickel hydroxide is chemically or electrochemically deposited in the pores of a 80—90% porous sintered nickel substrate that may also contain a reinforcing grid. 

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. 

Sintered Cells. Tlie fabrication of sintered electrode batteries can be divided into fwe principal operations preparation of sintering-grade nickel powder preparation of the sintered nickel plaque impregnation of the plaque with actwe material assembly of the impregnated plaques (often called plates) into electrode groups and into cells and assembly of cells into batteries. 

Eor the negative electrolyte, cadmium nitrate solution (density 1.8 g/mL) is used in the procedure described above. Because a small (3 —4 g/L) amount of free nitric acid is desirable in the impregnation solution, the addition of a corrosion inhibitor prevents excessive contamination of the solution with nickel from the sintered mass (see Corrosion and corrosion inhibitorsCorrosion and corrosion control). In most appHcations for sintered nickel electrodes the optimum positive electrode performance is achieved when one-third to one-half of the pore volume is filled with active material. The negative electrode optimum has one-half of its pore volume filled with active material. 

For many years, sintered-nickel electrodes have been used as the positive electrodes for sealed-type nickel-cadmium batteries. With an increase in the demand for high energy density, this type of elec-... 

Sintered Electrodes In these electrodes the active materials are present in pores of a sintered nickel support plate. This plate is manufactured by sintering of highly disperse nickel powder produced by thermal decomposition of nickel pentacarbonyl Ni(CO)5. The plates are filled by impregnating them in alternation with concentrated solutions of salts of the corresponding metals (Ni or Cd) and with an alkali solution serving to precipitate insoluble oxides or hydroxides. 

Cell construction is mainly confined to two types, using either pocket plate electrodes (vented cells) or sintered , bonded or fibre plate electrodes (vented and sealed cells). In the former, the active materials are retained within pockets of finely perforated nickel-plated sheet steel which are interlocked to form a plate. Positive and negative plates are then interleaved with insulating spacers placed between them. In sintered plate electrodes, a porous sintered nickel mass is formed and the active materials are distributed within the pores. In sintered plate vented cells, cellulose or other membrane materials are used in combination with a woven nylon separator. In sealed or recombining cells, special nylon separators are used which permit rapid oxygen diffusion through the electrolyte layer. 

Recently, cells employing thick sintered nickel plates on nickel-plated porous steel substrates have been developed which have greatly improved energy densities. The active material is introduced by electroprecipitation. Electrodes based on nickel fibre supports are also being studied. 

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

The electrodes are flat. The anode is composed of porous sintered nickel along with additives, which inhibit the loss of surface area during operation. The anode is in direct contact with the electrolyte matrix. The cathode is a porous nickel oxide, which is initially fabricated in the form of a porous sintered nickel and is subsequently oxidized during the cell operation. 

Fuel cells (FCs) are electrochemical devices that directly convert fuel energy into electricity without the need for a thermal cycle. They are essentially galvanic cells in which the electrodes only collect and convey electrical charges, but (unlike in the Volta pile and all other electric cells and batteries) they do not participate in the electrochemical reaction, since they are chemically and electrochemically inert conductors (amorphous carbon, sintered nickel oxide, etc.). 

Alkaline FCs (AFCs) use KOH as electrolyte and work at 70-90 C they are fully developed and very reliable (they powered on-board instrumentation of the Apollo spacecrafts and they power on-board instrumentation of the space Shuttles). Electrodes are mostly sintered nickel (anode) and sintered, lithiated nickel-oxide (cathode). 

Hic purity partially sintered nickel sheets were obtained from ERC (Electric Research Ciorp.). The porosity of these sheets varied firom 60% to 70%. The proprietary nature of these materials prohibits any release of the pore size distribution. Disks with a thickness of 30 mils and a diameter of 11/4" were cut from this material. This disks were soaked in 1 molar liOH, dried at 100X1, and oxidized in room air at 650 C for at least 8 hours to form a lithiated NiO stmcture. Gravimetric analysis of these electrodes showed that they were greater than 98% converted to NiO. 

The sintered nickel substrate for the cathode is similar to that used for Ni-Cd and Ni-MH cell constructions. The nickel active materials are loaded into the sinter plate using either an aqueous (Bellcore) or alcoholic-based (Air Force or Pickett) electrochemical impregnation process. A 5-10% cobalt additive is deposited with nickel hydroxide to improve charge acceptance. These electrodes have a significantly longer cycle life over the standard vacuum impregnated or pasted nickel electrodes used in commercial Ni-Cd cells. 

The sintered-type electrode is formed by filling of the nickel hydroxide active material into the sintered nickel porous layer on the punched steel metal. The pasted-type electrode is formed by filling of the nickel hydroxide active material into the formed nickel substrate with very high porosity. In the sintering layer of the sintered-type electrode, the pore size is around 10 pm and the porosity is approximately 75 %. On the coti-trary, in the formed nickel substrate of the pasted-type electrode, the pore size is around 500 pm and the porosity is approximately 95 %. Therefore, the sintered-type electrode is suitable for a high power use, and the pasted-type electrode is used for a high capacity battery [4]. 

Sintered Nickel Electrode in Alkaline Batteries These batteries are galvanic devices containing a porous Ni matrix that holds the active (anodic) materials. The following reaction is reversed upon discharging [16-17]... 

A variety of plate formulations are used in vented, sintered nickel-cadmium cells produced by different manufacturers. The plates differ according to the nature of the substrate, method of sintering, impregnation process, formation and termination techniques. The predominate plate fabrication process used for vented sintered plate over the years has been described by Heischer." There are several reviews on electrode fabrication processes that have been used in flooded vented cells. ... 

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