Researchers Breathe New Life into Ni-Fe Batteries

Thomas Edison developed the nickel-iron battery more than a century ago specifically to power electric cars. But the design has fallen out of favor except as a long-term storage device because it is slow to charge and discharge.

Now researchers at Stanford University say they have created an ultrafast nickel-iron battery than can be fully charged in two minutes and discharged in less than 30 seconds nearly 1,000 times faster than Edison's battery. The team details its battery design in the June 26 issue of the online journal Nature Communications.

The research team says the key to its design is electrodes made of carbon nanotubes and graphene (single-atom-thick sheets of carbon). The group says its battery has a specific energy of 120 Wh/kg and a specific power for 15 kW/kg.

The test battery built by the team is a one-volt prototype, but the researchers say the technology is "definitely scalable." They point out that the battery's ingredients nickel, iron and carbon are relatively inexpensive and widely available, unlike the rare earth metals in lithium-ion batteries. The electrolyte is a low-cost mixture of water and potassium hydroxide. Nickel-iron batteries also are considered stable and safer than lithium-ion batteries.

The electrodes of conventional nickel-iron batteries are made by mixing iron and nickel with conductive carbon. The Stanford researchers grew nanocrystals of iron oxide on graphene and nanocrystals of nickel hydroxide onto carbon nanotubes. They say the technique produced strong chemical bonding between the metal particles and carbon nanostructures, thus boosting performance.

The Stanford researchers envision their battery aiding an EV's lithium-ion battery rather than replacing it, mainly by acting as a capacitor-like device to quickly store and discharge electricity many times during a single trip. They say their system currently lacks sufficient energy density to become a substitute for today's EV batteries. The battery also loses about 20% of its ability to hold a charge after 800 cycles.