ZEBRA batteries

The electrolyte / " -alumina has already been described in Chapter III, Sec. 9. This section relates to additional information on the manufacture of / "-alumina and its application and behavior in high-tem-perature batteries (ZEBRA and Na /S). 

Recently the development of Na/S batteries for car applications has been abandoned only Na/S batteries for stationary applications (load leveling) are still under development in Japan. Among the high-temperature batteries, the ZEBRA battery is the only system at present which is being commercialized for car applications. 

Because of the less advanced status of the lithium aluminum/iron sulfide battery, only the ZEBRA battery and the Na/S battery are described in this section. 

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. 

Nickel chloride is preferred and ZEBRA batteries are based today on nickel chloride and sodium. According to the very simple cell reaction... 

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 ZEBRA cells are connected in series to obtain the demanded voltages, and chains of these cells are connected in parallel to obtain the capacity which is requested. At present there is a request from the car companies to obtain battery voltages close to 300 V, which means that about 110-120 cells will be connected in series in one string. The capacity of one... 

The performance of the ZEBRA battery system is shown in Table 3 ... 

Table 3. Data for ZEBRA batteries (including peripheral equipment)...

The battery system has reached more than 1700 cycles in life cycle tests. The calendar life of the /zebra battery has been proven to be close to five years in a continuing life test. In practical operation in cars the ZEBRA battery exceeded 110000 km within a three year period. This excellent result proves the ZEBRA battery to be a reliable system. 

Figure 8. Power density of ZEBRA batteries during discharge.

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. 

The electrolytes for ZEBRA batteries at AEG Anglo Batteries as well as for the NaS batteries at ABB are manufactured by the isostatic method. In contrast to this, Silent Power used electrophoretic deposition as the forming method for their so-... 

In the discharged state of ZEBRA batteries NaCl is formed in the positive electrode, which is beside the NaAlCl4. In abuse experiments, e.g., overheating, less volatile material will be released in the discharged state compared with the charged state where no NaCl is present. This is due to the lower vapor pressure of mixtures with increased NaCl content. 

The effects of Flix sediment pollution on invertebrates were examined at two levels. Local populations of zebra mussels and crayfish (P. clarkii) were sampled right over the Flix residue sediment, across the reservoir, in a meander immediately downstream the dam and in Asco, in addition to the Riba-roja reference site (Fig. 5a, b). Results from a battery of biochemical biomarkers (Fig. 5c) were similar... 

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.

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 ... 

One of the problems encountered with the Werth cell was an increase in resistance with cycling. This may have been caused in part by the /3-alumina reacting with the acidic sodium chloroaluminate melt. Coetzer had the idea of using transition metal chlorides as a positive electrode and chose a basic sodium chloroaluminate melt as the liquid electrolyte. This is compatible with /3-alumina, and a new class of secondary cells based upon the reaction between sodium metal and transition metal chloride has resulted from this work. Collectively, the term Zebra battery is used to describe this new class of cell. 

The Zebra battery is presently at the pilot line production stage. About 170 batteries are on test, mostly in vehicles but some on bench tests. The batteries are installed in passenger cars and in buses, and in the German electric vehicle fleet test on the island of Rugen, 52% of the 60 or so vehicles are equipped with Zebra batteries. A lifetime of 4 years, 1260... 

Zebra batteries have been subjected to a series of tests to demonstrate their ruggedness and safety. These include overcharge, short circuit, overheating and vibration and shock. Drop testing to simulate the effect of a... 

The related Zebra cell 205 uses the same solid electrolyte as in the Na-S battery, and operates at similar temperatures, but the cell reaction comprises the reaction of Na with NiCl2 to Ni and NaCl,... 

Fig. 4.25 Ragone plot comparing the internal combustion engine with the ZEBRA battery and fuel cells (very approximate). [The plot was introduced for comparing batteries (standardized to a weight of 300 kg) to include the performances of engines and fuel cells in a meaningful way their masses, together with the fuel carried, should be standardized to 300 kg.].

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. 

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