New metal alloy could improve performance of rechargeable batteries

The new alloy, produced by the US Department of Energy’s Brookhaven National Laboratory, is composed of the metals nickel, tin and lanthanum. According to researchers at Brookhaven, when their new alloy is used in nickel/metal hydride (Ni/MHx) batteries, it has a long-lasting ability to be charged and recharged and good resistance to corrosion. Even better, the alloy contains no expensive cobalt, and no toxic cadmium, both of which are usually found in rechargeable batteries. “This new alloy is inexpensive and relatively environmentally benign,” said research team leader James Reilly.

Although regular rechargeable batteries have a greater ability to store hydrogen atoms, and therefore a greater initial charge capacity than those using Brookhaven’s new alloy, these hydrogen atoms cause the crystal lattice in which they are stored within the batteries to expand, and then contract as the battery discharges. “This expansion and contraction is repeated in each charge/discharge cycle of the battery, which pulverises the alloy into small particles that are more susceptible to corrosion,” said Reilly. “That’s why batteries don’t recharge an infinite number of times. Eventually, corrosion takes over.”

In order to counteract this effect in the past, cobalt has been used to stabilise the lattice. However, even small amounts of cobalt are so expensive that for batteries of the sizes needed in electric vehicles, the costs are prohibitive, say the researchers.

Instead of cobalt, however, Brookhaven’s new alloy uses a 1:5.157 ratio of lanthanum to nickel/tin, in which ‘dumbbells’ of two atoms of nickel carry out the stabilising role. These nickel ‘dumbbells’ make the structure more compact, which decreases its ability to store hydrogen, but also decreases the alloy’s tendency to corrode, increasing its long-term energy storage capacity, says Thomas Vogt, one of the researchers.