A British defense technology company, Qinetiq, is testing a new type of lithium-ion battery for hybrids and electric vehicles that could be substantially cheaper and more powerful than existing batteries.
The battery is based on lithium-ion iron-sulfide chemistry, which has a number of advantages over the chemistry of existing batteries, says Gary Mepsted, technical manager for Qinetiq's power sources group. The new battery would cost half as much as existing vehicle batteries and could last longer and recharge more quickly that other lithium batteries. Mepsted says that compared to standard lithium-ion batteries, the new battery has demonstrated about 1.6 times the energy density (which would extend a plug-in electric's range) and a 50 percent higher power density (which would let hybrids charge and discharge more rapidly).
Packing power: The new battery pack, designed for a prototype hybrid diesel vehicle, is made with a novel lithium-ion chemistry that could boost the battery’s performance while bringing down the cost.
Researchers have long viewed lithium-ion batteries as an attractive alternative to the expensive metal-based batteries now used in hybrids. But although standard lithium-ion batteries are relatively cheap and can store about twice as much energy as standard nickel metal hydride cells, developers have had to overcome a number of technological challenges to make them practical for vehicles.
Plug-in electric vehicles need batteries with higher energy densities to extend their range between charges, says Mepsted. And for hybrids, the power density of standard lithium-ion batteries is less than ideal for coping with the rapid charging and discharging that comes with the regenerative braking systems used in hybrids.
Another issue is safety, says Jeff Dahn, a professor of physics and chemistry at Dalhousie University in Halifax, Canada. In small devices like cell phones, this is less of an issue, he says. "But in large cells, it's hard to remain stable under abuse conditions." Such conditions include overcharging or collisions, which can cause the batteries to combust or even explode.
Qinetiq's approach involves making cathodes from lithium-ion iron sulfide instead of the more common lithium-cobalt oxide. Because this chemistry results in two lithium ions for every sulphide, it creates a massive increase in energy density.
Cost is a major issue, says Dahn. "Batteries are about three to five times more expensive than what we want," he says. But while there are energy and cost advantages to using iron sulfide, it can be problematic to use in manufacturing. "Iron sulfide is stable in air, but when you react it with lithium it loses this stability," he says.
Qinetiq says it has solved this issue, although the company won't go into details about how. Based on early estimates, using low volumes of materials, the new batteries should be half the cost of conventional nickel-metal hydride batteries, Mepsted says.
Developed as part of a $3.2 million two-year project in collaboration with Ricardo, based in Warwickshire, the battery has so far been tested under only limited conditions. In the lab, the cell has demonstrated 50 percent improvements in discharge rates. "There needs to be more development in the cell chemistry before it could be considered for production," says Colin Wren, a researcher at Ricardo. But because it can be tailored for either high energy density or high power density, he says, the technology is suited to both plug-in electrics and hybrids.
By Duncan Graham-Rowe
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