Sodium nickelate

The second electrolyte, the melt of sodium aluminum chloride, provides another advantage for the ZEBRA system. This second electrolyte makes the system tolerant to overcharge and overdischarge. In the overcharge reaction NaAlCl4 reacts with nickel to form sodium, nickel chloride, and... 

The high ionic conductivity of sodium (3"-alumina suggested that it would form a suitable electrolyte for a battery using sodium as one component. Two such cells have been extensively studied, the sodium-sulfur cell and the sodium-nickel chloride (ZEBRA) cell. The principle of the sodium-sulfur battery is simple (Fig. 6.13a). The (3"-alumina electrolyte, made in the form of a large test tube, separates an anode of molten sodium from a cathode of molten sulfur, which is contained in a porous carbon felt. The operating temperature of the cell is about 300°C. 

Figure 6.13 Batteries using p"-alumina electrolyte, schematic (a) the sodium-sulfur cell and (b) the sodium-nickel chloride (ZEBRA) cell.

The metal content can range from only a few parts per million to >1000 ppm. Trace elements such as iron, sodium, nickel, vanadium, lead, and arsenic can corrode metallic parts and damage heating equipment. Low levels of nickel, vanadium, and copper are known to deactivate refining catalysts. 

Among the elements that make up rocks and minerals, silicon, magnesium, and iron are of almost equal abundance followed by sulfur, aluminum, calcium, sodium, nickel, and chromium. Two of the most common minerals in meteorites and in the terrestrial planets are olivine ((Mg,Fe)2Si04) and pyroxene ((Mg,Fe,Ca)Si03). The composition obtained by averaging these two minerals is very similar to the bulk solar system composition, so it is really no surprise that they are so abundant. 

Strong contenders for automotive power are the sodium/sulphur and sodium/ nickel chloride batteries, the latter known as the ZEBRA cell. ZEBRA was originally (c. 1979) an acronym devised for commercial security reasons but now it stands for the very apt Zero Emissions Batteries Research Activity . Several European car manufacturers including BMW and Mercedes have incorporated the ZEBRA cell into prototype cars, vans and buses. The performance of the battery far outstrips that of the lead/acid counterpart, as is evident from Fig. 

Dvorak W, Sodium-nickel-chloride cell. In Wikimedia Commons CC-BY, 2011. Available from http //commons.wikimedia.Org/wiki/File Sodium-nickel-chloride cell.svg. 

The contents of sodium, nickel and manganese in the samples were determined by Seiko Instruments SPS7000A induced couple plasma (ICP) spectrometer after dissolved in a mixed solution of HCl and H2O2. 

Manganese dioxide, sodium nickel hexacynaoferrate, hydrous titanium oxide, zirconium phosphate, ferric hydroxide, different commercial sorbents... 

Nickel oxide electrodes constitute the positive plates of several storage systems (among which nickel-zinc, nickel cadmium, nickel metal-hydride, sodium-nickel chloride) [16]. In recent years, the high-specific energy and specific power of Ni-Zn systems has increased the interest in their use for electric vehicles with respect to the past years, when their application was essentially limited by a short cycle life. 

The last type of nickel based battery here considered is the so-called sodium-nickel chloride or Zebra battery, firstly developed in 80s in Pretoria, South Africa (Zebra stands for ZEolite Battery Research Africa). The anode is made of liquid sodium, the electrolyte is based on sodium ion conducting -alumina and the cathode is constituted by nickel chloride. This is flooded with liquid NaAlCU which acts as a secondary electrolyte, i.e., its function is to enhance the transport of sodium ions from the solid nickel chloride to and from the alumina electrolyte [19]. They work at high temperature (157°C is the temperature necessary to have sodium in its molten state, but the better performance is obtained in the range 250-350°C) and operate with the following discharge semi- reactions at the anode ... 

Ni/MH = nickel/metal hydride, VRLA polymer = valve-regulated lead-acid, Na/NiCL = sodium/nickel chloride, Li- ion = lithium-ion, Li polymer = lithium-... 

Safer versions of the lithium battery such as lithium-polymer are also being developed and are already available in small cells. Other battery chemistries (e.g., sodium/nickel chloride (Na/NiCL), nickel/zinc (Ni/Zn)) may be found in small numbers, but will... 

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