Overcharging reaction

The overcharge reactions for the cell are the same as for nickel—cadmium and nickel—hydrogen cells. The oxygen generated on the nickel electrode at the end of charge and overcharge finds its way to the anode and reacts to form water in the Ni—H2 case and Cd(OH)2 in the Ni—Cd case. 

Overcharge Reactions. Water electrolysis during overcharge is an irreversible process. Oxygen forms at the positive electrode ... 

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 cell reactions are shown in Fig. 8.21, from which it can be seen that overdischarge and overcharge reactions are possible. Use is made of the overdischarge reaction to allow the assembly of the cell without the addition of elemental sodium. To the products of the discharge reaction - nickel and sodium chloride - is added a small quantity of aluminium which on the first charge generates enough excess sodium to prime the sodium electrode ... 

Sufficient sodium chloride is added to chlorinate over 30% of the nickel, after which the overcharge reaction occurs in which sodium chloride is abstracted from NaAlCU to give an AlCl3-rich melt. 

Fig. 9.15. Representation of primary charge-discharge processes and overcharge reactions in VRLA cell. Vertical arrow just to the left of j-axis denotes potential for oxygen reduction to water.

Figures 10.1 and 10.2 compare the 12-V overcharge reaction divided into four regions, and provide a diagram of the factors affecting the increase in the cell temperature during a portion of the overcharge tests. Regions III and IV should be...

The finishing charge and overcharge reactions that electrolyze water form a mixture of hydrogen (H2) and oxygen (O2) gases. At the positive plate, [8]... 

The total overcharge reaction is the electrolysis of water to form oxygen and hydrogen [10]... 

This corresponds to an overcharge reaction and requires a higher voltage than 3.05 V. 

As commented in CeU Chemistry, mechanical damage in a ceramic electrolyte is recovered even in the mechanical damage. And hquid electrolyte reacted with the hquid sodium forms layer of salt and aluminum equal to the overcharge reaction. This reactirm reduces the thermal load by about 1/3 compared to the total electrochemicaUy stored energy. CeU case was closed by TCB to stand up to 900 °C. Thermal insulatirHi material is made out of foamed Si02. This is thermally stable over 1,000 °C, and the heat conductivity is very low (only 0.006 W/mK) in the vacuum insulation box. Even when the vacuum environment... 

Overcharge reaction. The charge capacity of the ZEBRA cell is determined by the quantity of salt (NaCl) available in the cathode. In case a cell is fully charged and the charge voltage continues to be applied to the cell for whatever reasons, the liquid salt NaAlCU supplies a sodium reserve following the reversible reaction... 

This overcharge reaction requires a higher voltage than the normal charge, as illustrated in Figure 10.5. This has three practical very welcome consequences ... 

Barrier by the chemistry. In case of severe mechanical damage of the battery the brittle ceramic breaks, whereas the cell case made out of steel is deformed and most likely remains closed. In any case the liquid electrolyte reacts with the liquid sodium to form salt and aluminum equal to the overcharge reaction described above. These reaction products form a layer covering the NiCl2 cathode and thus passivate it. This reaction reduces the thermal load by about 1 /3 compared to the total electrochemically stored energy. 

The reactions that produce the gases are called the overcharge reactions. These reactions differ depending on whether one deals with a sealed or vented ceU. 

The result in a sealed cell is that electricity is converted into heat without any net chemical change in the cell. The overcharge reaction is exothermic, particularly the chemical recombination reaction in the sealed cell. 

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