Charge ZEBRA cell

The thermoneutral potential is 2.72 V this means that during charging at voltage below this value ZEBRA cells will be cooled thermodynamically. 

The ZEBRA cell shows the similar behavior during the charging reaction, in which the nickel is converted to nickel chloride within the reaction front. During the charging reaction the reaction front also moves from the / " -alumina into the positive electrode. 

One innovative aspect of the ZEBRA technology is that the cell is constructed with the reaction products , metallic nickel and sodium chloride in situ that is the cell is in the discharged state, greatly facilitating fabrication. The liquid sodium and nickel chloride are formed by charging the cell. 

Fig. 4.35 Schematic of the Na/NiCl2 ZEBRA cell (charged state).

The charge capacity of the ZEBRA cell is governed by the quantity of NaCl available in the positive electrode. During an operation, the liquid salt NaAlCU is a Na reserve as shown in the following reaction ... 

Charging of ZEBRA cells and batteries is at a 6 h rate for normal charge and 1 h rate for... 

At a charged state, positive and negative electrode could be NiQ2 and Na metal. It is quite difficult to handle these materials in a production scale, and the cell is usually built with NaQ and Ni metal as discharged products. In order to maintain the sufficient utilization of Na electrode, A1 powder is incorporated in the positive electrode side to form NaAlCU that can be an electrolyte when the electrode materials are melted. Operation temperature is at around 270-350 °C. Sodium ion conductivity has a practical value (>0.2 - 1 cm ) at 260 °C and is temperature dependent with a positive gradient [3]. Thus, the operational temperature of ZEBRA batteries has been chosen for the range above. Current collector for positive electrode is Cu wire with Ni plating. 

There is no side reaction in the cell chemistry of ZEBRA battery, and therefore, the charge and discharge cycle has almost 100 % efficiency. This is due to the ceramic electrolyte. Figure 2 shows a first charge and discharge curves of Na/NiCl2 ceU assembled in a discharged state [4]. This ceU contains no additives like FeS. 

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