In 1901, Thomas Edison developed the recharcheable nickel-iron battery, a technology he hoped to see implemented in electric cars. But a slow rate of energy output and slower charging time saw it superseded by lead-acid and lithium-ion batteries in standard and electric cars alike.
Now, more than a century after it was first developed, the "Edison battery" has been reborn — and it's faster, cheaper and more powerful than ever. Will it find new life in the electric vehicles of tomorrow?
The original Edison battery was lauded for its endurance and reliability, but the power supply had significant drawbacks. The typical nickel-iron battery requires several hours to charge, and the rate of discharge is prohibitively slow.
To address these shortcomings, a team of researchers led by Stanford University chemist Honjie Dai decided to give Edison's ideas an upgrade by future-fitting the inventor's early 20th century design with 21st century nanotechnology. The result was a revamped Edison battery capable of charging and discharging nearly 1,000 times as fast as the original.
The researchers' redesign relies on some clever carbon chemistry, which is published in the latest issue of Nature Communications and summarized in the diagram featured here [click to enlarge]. Carbon is often used to improve electrical conductivity in electrodes; the issue, explains lead author Hailiang Wang, is using that carbon to its full potential:
In conventional electrodes, people randomly mix iron and nickel materials with conductive carbon. Instead, we grew nanocrystals of iron oxide onto graphene [single-molecule-thin sheets of carbon arranged in a honeycomb lattice], and nanocrystals of nickel hydroxide onto carbon nanotubes [cyclinders of carbon molecules, also arranged in a honeycomb lattice].
The resulting chemical bonds had a remarkable effect on battery performance. "Coupling the nickel and iron particles to the carbon substrate allows electrical charges to move quickly between the electrodes and the outside circuit," explained Dai. "The result is an ultrafast version of the nickel-iron battery that's capable of charging and discharging in seconds."
The researchers have already implemented their redesign in a one-volt, "ultrafast" prototype battery, capable of charging in 2 minutes and discharging in 30 seconds. The tiny energy source packs just enough punch to operate a flashlight, but big things have small beginnings; already the team is looking for applications in everything from vehicles to electrical infrastructure.
"It's definitely scalable," Wang said. "Nickel, iron and carbon are relatively inexpensive. And the electrolyte is just water with potassium hydroxide, which is also very cheap and safe. It won't blow up in a car."
That being said, the battery's energy density is still too small for it to serve as a standalone energy source, "but it could assist lithium-ion batteries by giving them a real power boost for faster acceleration and regenerative braking," notes Wang.
The battery's only other major pitfall is that it's prone to losing up to 20% capacity over 800 charging cycles (that's comparable to a lithium-ion battery, but the authors cede that the speed of their battery would likely mean hitting the 800 mark sooner than with a traditional power source).
All told, however, the redesign has implemented some truly creative chemistry to bring an age-old technology back into contention, heralding what the researchers describe as "a new generation of Ni–Fe batteries as novel devices for electrochemical energy storage."
The researchers' findings are published in this week's issue of Nature Communications.