Battery spells good news for energy

Scientists have given a 21st-century makeover to the nickel-iron battery, a gadget conceived by Thomas Edison during the era of the steam engine and horse and buggy. The upgraded battery can be recharged in around two and half minutes, as opposed to several hours at present, and discharges in under 30 seconds. Because it can store and release energy so quickly, the battery could be a boon for the renewable-energy industry and also help power cars as Edison originally envisaged, the researchers say. Devised by Edison and fellow inventor Waldemar Jungner in 1902, the nickel-iron battery comprises two electrodes, one made of nickel and the other of iron, that are immersed in an alkaline solution. Its advantage is that materials are abundant and cheap and the solution is relatively harmless compared to toxic lead-acid batteries. Nickel-iron batteries were marketed for cars until the 1920s, but then dropped out of the picture because they were not as powerful as petrol and diesel fuel engines. Another downside was that they took a long time to recharge. They remained a robust backup power source for railways, mines and other industries before falling out of favor in the mid-1970s. Today, just a handful of companies make the batteries, mainly to store surplus electricity from solar and wind generators and release it during times of peak demand. The new-generation battery comes courtesy of a team led by Hongjie Dai, a chemistry professor at Stanford University in California. They have bonded the electrodes to carbon nanotubes and to graphene, a super-material made of carbon just one atom thick, gaining a dramatic boost in conductivity. "Coupling the nickel and iron particles to the carbon substrate allows electrical charges to move quickly between the electrodes and the outside circuit," Dai said in a press release. "The result is an ultra-fast version of the nickel-iron battery that's capable of charging and discharging in seconds." So far, Dai's lab has made a small one-volt prototype that can operate a flashlight. Size for size, it has nearly 1,000 times the density energy of traditional nickel-iron batteries. Scaling up the lab gadget to bigger applications should not be a problem, and it should find a ready outlet in situations where a quick jolt is needed from a power source that is easily replenished. "Our battery probably won't be able to power an electric car by itself, because the energy density is not ideal," said researcher Hailiang Wang. "But it could assist lithium-ion batteries (in cars) by giving them a real power boost for faster acceleration." The battery could then be replenished from regenerative braking. The chemical mix used in the battery is water with potassium hydroxide, which is stable, cheap and safe, he added. The prototype does have a hitch, in that after lots of cycles of recharging, it no longer holds the charge so well. After 800 cycles, the charge decays by about a fifth, a problem the Stanford team hopes to fix. The research was published on Tuesday in Nature Communications.