Hi-Voltage Cells Extend Range
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PROTOTYPES built by European car makers have travelled 200 km on a single charge  |
 FOR SAFETY: A double-walled stainless battery box |
Sodium-nickel chloride batteries power zero-emission electric vehicles
Nickel magazine, Mar. 01 -- A nickel-based battery could play a key role in powering the
pollution-free electric vehicles of the future. Dubbed the "Zebra" battery, the high-energy unit has powered
prototype cars for more than 200 kilometres on a single charge and has run as efficiently in desert heat as
it has in Arctic cold.
A Swiss company, MES-DEA, is building the battery at its Beta Research & Development Ltd. plant in Derby,
England, harnessing the chemical reaction between nickel and ordinary salt (sodium chloride) to create three
times the electrical charge -- 100 kilowatt-hours per kilogram of battery weight -- as a conventional
lead-acid battery.
Compared with other batteries which are vying for a share of the electric vehicle market, the specific energy of the Zebra battery is more than 50% higher than that of nickel metal hydride batteries and is similar to that of lithium ion batteries.
"It translates almost directly into giving the electric car three times the range of a car with a lead-acid battery," notes Roy Galloway, a senior scientist with Beta R& D and one of the battery's developers. "It's a higher-voltage cell and that's very important for high-power applications such as electric vehicles."
The Zebra battery was developed on the basis of research that begun in the 1970s by a South African, Johan Coetzer, and the name pays homage to its African roots. It uses nickel in three forms, the most important being a commercially available powder -- Inco battery grade (carbonyl) 287 -- that serves as the positive electrode. About 120 grams of powdered nickel are required for each of the 216 cells that make up a single battery, which generates enough power to run a compact car. The metal reacts with salt to form nickel chloride and sodium when the cells are charged.
Nickel again comes into play as the current collector -- a copper rod clad with nickel alloy N02200 that carries the electric current to and from the battery. The sodium is contained in mild steel cell cases and these cells are housed inside a double-walled stainless steel (X5CrNiMoTi17-12-2) battery box.
Beta expects each battery to last more than a decade -- a long career in the world of electro- chemical technology. Once exhausted, it can be recycled as a nickel-rich feedstock to produce stainless steel. In the event of a severe crash, the two liquids (molten sodium and molten sodium aluminium chloride) combine to form solid sodium chloride and aluminium. Large Zebra batteries have passed all European Car Federation tests including a 30 miles-per-hour impact and penetration test and a 30-minute petroleum fire.
The battery creates a lot of heat, running at 250 to 270°C, which can be harnessed to warm the passenger compartments of vehicles in cold climates. Field trials have proven it is the only battery system that performs identically in the Arizona desert and on the frozen lakes of Sweden. In daily use, no energy is required to maintain battery temperature. "That's pretty important if you're selling a car to the public," says Galloway. "You don't want someone who lives in the cold climate to have a different performance to one that lives in a hot climate." Unlike other batteries, the Zebra won't lose its charge if left unused, and so it is ideal for use in vehicles and as an emergency power source for industry.
Several European car makers, including Mercedes, BMW, and Zytek Automotive (a British producer of high-performance engines), have incorporated the Zebra into prototype cars, vans, and buses. So far, Beta produces only several hundred of the batteries each year, but the future looks bright for their use in vehicles driven shorter distances, especially within cities. "It won't be the only type of car," Galloway predicts, "but it could become quite a large market eventually."
Photo: MES-DEA
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Beta Research & Development Ltd. |
