ZEBRA system/cell

The ZEBRA battery is a high-energy battery based on a cell with electrodes of sodium and metal chloride. The ZEBRA system was first described by Coetzer in 1986 12J. 

The molten salt, sodium aluminum chloride, fulfills two other tasks in the cell system. The ceramic electrolyte "-alumina is sensitive to high-current spots. The inner surface of the ceramic electrolyte tube is completely covered with molten salt, leading to uniform current distribution over the ceramic surface. This uniform current flow is one reason for the excellent cycle life of ZEBRA batteries. 

The molten salt electrolyte also contributes to the safety behavior of ZEBRA cells. The large amount of energy stored in a 700 g cell, which means about 30 kWh in a 300 kg battery, is not released suddenly as heat as be expected in a system with liquid electrodes such as the sodium sulfur cell. In the case of accidental destruction of ZEBRA cells, the sodium will react mainly with the molten salt, forming A1 sponge and NaCl. -The diffusion of the NaAICI ... 

The safety of the ZEBRA battery has been proven extensively by abuse testing overheating, overcharging, short-circuiting of battery terminals and of cell groups, crash tests on the battery itself by dropping it at 50 km h 1 onto a pole or spike, and crash tests of cars with built-in ZEBRA batteries at 50 kmh-1 [10]. The results of abuse testing prove the ZEBRA battery to be a safe battery system. 

Figure 18. Phase diagram of the NaCl - NiCI2 system. The stipled area is the operating region of the ZEBRA cell.

Currently interest has now been directed toward a similar high temperature system, the ZEBRA Battery, which also uses P-alumina as a Na ion conductor. The sulfur electrode is replaced by nickel chloride or by a mixture of ferrous and nickel chlorides. Contact between the NiCl2 electrode and the solid electrolyte is poor as they are both solids, and current flow is improved by adding a second liquid electrolyte (molten NaAlCb) between this electrode and the P-alumina. The overall cell reaction is now ... 

Also in Germany, Mercedes-Benz has been developing electric vehicles for over 30 years. Many of the later vehicles utilized advanced sodium—nickel chloride (ZEBRA) batteries. By 1997, over 1 million km of road testing of these batteries had been accumulated, much of it in the electric version of the Mercedes-Benz A-Class car. In 1994, the company commenced its research on fuel cell vehicles - the New Electric Car (NECAR) programme. Following the evaluation of a series of prototypes, the NECAR 5 was launched in November 2000. This, too, was based on the A-Class car. Power was supplied by a 75 kW fuel-cell system that was fed by an on-board methanol reformer. The car featured a cold-start facility to remove the need for the reformer to... 

Another type of battery is the so-called Zebra cell, obtained for the first time in South Africa by Coetzer [425] at Zebra Power Systems (Pty) Limited. The development of this battery is being actively pursued in the United Kingdom for high energy density applications such as electric vehicles, load leveling and spacecraft. This type of battery has sodium as the negative electrode, and the positive electrode is made from Fe/FeCl2 or Ni/NiCU. 

TuttoTransporti/Marcopolo (Brazil). In 1995 under the frame of the UNDP scheme a project was signed to show the advantages of fuel cell technology for Brazil. The hybrid powertrain was integrating two Hy80 fuel cell systems (Daimler) and three Zebra batteries in the vehicle back [52]. 

Small cracks in the ceramic electrolyte can be closed by formed salt and Al. When crack is larger, formed Al short-circuits between positive and negative electrode. This cell loses voltages, but still the whole system can be operated as long as failed cell was within 5-10 % of the total cells. The battery controller detects this and adjusts all operative parameters. In this meaning, ZEBRA battery is failure tolerant to some extent. 

Brett DJL, Aguiar P, Brandon NP, Bull RN, Galloway RC, Hayes GW, Lillie K, Mellors C, Smith C, Tilley AR (2006) Concept and system design for a ZEBRA battery-intermediate temperature solid oxide fuel cell hybrid vehicle. Concept and system design for a ZEBRA battery-mediate. J Power Sources 157 782-798... 

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