Positive nickel electrode material

Electrochemical Design. The electrochemical design of the cell consists primarily of balancing the active materials present in the electrodes. This previously has been discussed for each of the two electrodes separately, the nickel positive electrode and the zinc negative electrode. When combined in the cell, the two active materials must be present in some ratio with respect to each other. As with most other alkaline nickel batteries, the nickel-zinc system is typically positive (nickel electrode) limited. This means that the cell contains more zinc active material, on an Ampere-hour basis, than nickel active material. This must take into account the active materials present in the cell in addition to the active material utilization of each. 

In this cell design the positive nickel electrode is sealed to a metallized j5-alumina collar which is then attached to a -alumina canister by a glass seal. This assembly is then welded onto a mild steel can and the space in between filled with sodium metal. The -alumina tube is then filled with positive electrode material namely nickel powder, sodium chloride and aluminium powder. 

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. 

In acidic electrolytes only lead, because it forms passive layers on the active surfaces, has proven sufficiently chemically stable to produce durable storage batteries. In contrast, in alkaline medium there are several substances basically suitable as electrode materials nickel hydroxide, silver oxide, and manganese dioxide as positive active materials may be combined with zinc, cadmium, iron, or metal hydrides. In each case potassium hydroxide is the electrolyte, at a concentration — depending on battery systems and application — in the range of 1.15 - 1,45 gem"3. Several elec-... 

Unlike the cathodic reaction, anodic oxidation (ionization) of molecular hydrogen can be studied for only a few electrode materials, which include the platinum group metals, tungsten carbide, and in alkaline solutions nickel. Other metals either are not sufficiently stable in the appropriate range of potentials or prove to be inactive toward this reaction. For the materials mentioned, it can be realized only over a relatively narrow range of potentials. Adsorbed or phase oxide layers interfering with the reaction form on the surface at positive potentials. Hence, as the polarization is raised, the anodic current will first increase, then decrease (i.e., the electrode becomes passive see Fig. 16.3 in Chapter 16). In the case of nickel and tungsten... 

However, it is recognized that slightly soluble intermediates such as CdO(OH) and Cd(OH)3 are involved. Cadmium does not corrode since its equilibrium potential is more positive than that of hydrogen in the same solution. The active material in pocket plate cells consists of metallic cadmium, with up to 25% of iron and small quantities of nickel and graphite to prevent agglomeration. Two methods of preparation are used. One involves the electrochemical co-reduction of a solution of cadmium and iron sulphate in the other, dry mixtures of cadmium oxide or hydroxide and Fe304 or iron powder are used. In some methods of pocket plate manufacture, the electrode material is pressed into pellets or briquettes before being inserted into the pockets, and various waxes or oils may be used to facilitate this process. 

Pocket-type cadmium electrodes are made by a procedure similar to that described for the positive electrode. Because cadmium active material is more dense Ilian nickel active material, and because cadmium has a 2+ valence, cadmium electrodes, when fabricated to equal thicknesses, have almost twice the working capacity of the nickel electrode. 

Nonactive/slightly reactive electrode materials include metals whose reactivity toward the solution components is much lower compared with active metals, and thus there are no spontaneous reactions between them and the solution species. On the other hand, they are not noble, and hence their anodic dissolution may be the positive limit of the electrochemical windows of many nonaqueous solutions. Typical examples are mercury, silver, nickel, copper, etc. It is possible to add to this list both aluminum and iron, which by themselves may react spontaneously with nonaqueous solvent molecules or salt anions containing atoms of high oxidation states. However, they are not reactive due to passivation of the metal which, indeed, results from the formation of stable, thin anodic films that protect the metal at a wide range of potentials, and thus the electrochemical window is determined by the electroreactions of the solution components [51,52],... 

Some of the more exotic electrode materials are nickel coated with manganese, tungsten or ruthenium oxides for positive electrodes. These metals give quicker action for the part of the reaction that occurs at the positive electrode. Nickel plated platinum can be used on the negative... 

---