One of the promising future batteries for electric propulsion of vehicles and ships is the sodium/nickel chloride or ZEBRA battery. Despite some disadvantages with respect to the high temperature, the advantages with respect to specific energy and energy density are such that, especially in applications where the battery is used on a more or less continuous basis (e.g., in delivery vans and taxies) it is an interesting candidate battery. Another interesting application is on board of ships, like submarines or future electrical surface ships with electric propulsion.
The ZEBRA battery has an attractive specific energy and power (90 Wh/kg and 150 W/kg). The liquid electrolyte freezes at 157 C, and the normal operating temperature range is 270-350 C. The β-alumina solid electrolyte that has been developed for this system is very stable, both to sodium metal and the sodium chloroaluminate. Lifetimes of over 1500 cycles and five years have been demonstrated with full-sized batteries, and over 3000 cycles and eight years with 10- and 20-cell modules. Vehicles powered by ZEBRA batteries have covered more than 2 million km.
However Zebra battery chemistry is expensive and fairly heavy, compared to NiMH and Li-ion, but it is very robust against deep cycling (down to 20% charge), even at high discharge rates and extreme ambient temperatures. But, the battery must be heated, which is efficient only in vehicles such as city buses, delivery trucks, garbage trucks etc. that operate frequently at low speeds for extended periods.
It has also found application as a fixed storage alternative to offset peak energy demand in some electrical generating stations.
The Halton Hills Hydro, a small electricity producer in Acton, Ontario, installed a system comprising five 20-kilowatt-hour sodium-nickel chloride batteries and software that automatically determines the best time to charge and discharge the power. The project commenced in July 2006.
All of the electronics and power management systems used in Halton Hills are commercially available, and no specialized electrical work was required. ZEBRA batteries are the key to the system. They can store electricity more efficiently than hydrogen fuel cells, where the overall energy efficiency is about 18 percent. A ZEBRA battery system can meet or exceed 80 percent AC-to-AC efficiency.
Another area where these batteries show great promise is as a safer alternative to lead-acid technology that can also meet the power demands of a submarine.
More information can be found at http://www.betard.co.uk/, home of Beta Research and Development Ltd., very active in ZEBRA battery technology.
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